» Minilab scanning devices
We continue to familiarize ourselves with the principles and features of the work of mini-photo laboratories. Let's try to understand how the density and color characteristics of a negative are measured and exposure parameters are calculated.
To see and analyze what you see (in our case, a negative image on film), you must, at a minimum, have “eyes and brains.” The functions of these organs in the minilab printer are performed by the scanner. Features of the image reading method and the algorithm for processing the received data determine the degree of reliability of calculating the exposure time to obtain a high-quality print.
As for the “eyes” of the scanner, the more detailed information they report the negative to the computer (the greater the resolution and dynamic range measuring system) - so much the better. However, in reality, the amount of information processed is limited by the capabilities of the computer hardware and algorithm and the processing time, which must be consistent with the performance of the rest of the printer systems. Moreover, the task that the scanner is designed to solve is not only and not so much in compensating for the previously described factors associated with the negative, paper, optical and chemical paths of the printer. The scanner's algorithm should, ideally, classify the shooting conditions of the object and calculate the correction for its optimal reproduction on the print. It should be borne in mind that the task of determining the subject of photography often cannot be unambiguously solved not only by powerful software and hardware, but also by the operator himself, since ideal density correction for one area of the image can lead to loss of detail in another area. For example, a face in the foreground “embossed” by a flash has a much higher density on the negative than background objects, which may be of no less interest to the shooter. In this case, a better compromise may be to print the foreground object slightly denser to reproduce background detail. The problem of reproducing details simultaneously from areas of the negative of high and low density is solved by adaptive masking used in the printer newest generation Agfa MSP DIMAX. A liquid crystal matrix is introduced into the optical path, on which a masking image is automatically formed, compensating for the high contrast of the original negative.
Let's try to figure out how scanners of different printer models ( Noritsu QSS1401/1501/1201(2)/1701(2), Gretag MasterOne/MasterLab(+), Agfa MSC) cope with such a complex task, and to what extent their functioning can be optimized by tuning.
Through the eyes of a scanner Noritsu is a CCD matrix of 128x128 elements onto which a frame is projected through a lens corresponding to the film format. The image is read three times using filters R, G, B. Lenses and filters are located on coaxial turrets. After pre-amplification, the information in the form of an analog video signal is supplied to the scanner’s processor board, where it is digitized and analyzed. Despite the fairly high resolution of the CCD matrix and the solid computing power of the processor, this scanner often makes mistakes when calculating exposure. This is due to both the imperfection of the algorithm and the properties of the measuring system: the characteristics of the filters are not adapted to the spectral sensitivity of photographic paper and are unstable over time (filters quickly burn out). The dynamic range of the measurement system is not sufficiently adapted to the full range of image densities on film. Setting up the printer when working with a scanner involves calibrating the signal amplification (with potentiometers on the pre-amplifier board), determining the area of the CCD onto which the frame is projected (for each film format), and remembering the values for the unexposed frame of the film. Practice shows that, to reduce the percentage of defects, operators Noritsu prefer to work in semi-automatic mode, when the scanner corrects only color shifts, and the operator enters density corrections. The color correction function deteriorates as the filters burn out, and often the role of the scanner is reduced to positioning the frame.
Scanner of mentioned models Gretag works much more effectively when determining correction for both density and color. Its measuring system is a line of photodiodes that scans the frame in 12 positions behind each of the R, G, B filters (for a full 135 format frame, an 8x12 data array of points is scanned for each color) ( Fig.1). Such a small resolution imposes certain limitations on the efficiency of recognizing small objects, but the processing algorithm does a good job of classifying typical scenes. The line of photodiodes is the only organ of vision of the printer (printers Noritsu, in addition to the scanner matrix, have three photosensitive sensor R,G,B, performing integral measurement of frame density). Therefore, working without a scanner is only possible in fixed exposure mode. Signals from the photodiodes, after adaptive amplification, are digitized by a 12-bit ADC, which provides a sufficient dynamic range of the measuring system. The algorithm classifies the image, trying to classify it into one of the groups according to shooting conditions (Flash-1, Flash-2, Back Light, Green, Snow). For each group, the probability of a subject being assigned to it is estimated, and the resulting values are involved in the process of calculating the exposure time, along with the parameters in the printer’s memory that determine the degree of correction for each of the groups. The Flash-1 group includes scenes with a pronounced high-density object in the center of the frame (it is assumed that the foreground object was shot with flash and a plus density correction is required for its normal reproduction). A typical example is a face in the foreground shot with flash. If one or more dense areas of the negative are offset from the center, the scanner analyzes their color balance and, if close to the balance of human skin, takes them for the subject, classifying the plot as Flash-2, and, just as in the previous case, performs a positive density correction . The scanner assigns a scene to the Back Light group (bright background) if it detects a sufficiently large area of high-density negative, limited to the edges of the frame. This area is classified as a bright background and a minus density correction is applied. A typical example is a bright sky in the background. Scenes with objects against a brightly lit green background are classified as the Green group and require minus correction. It should be noted that although the scanner takes into account color balance when assigning scenes to the Flash-2 and Green groups, the corresponding correction is made only for density. The scanner classifies low-contrast objects on a uniform light background (snowy landscape, sky) into the Snow group. Such stories require negative correction. Special buttons on the keyboard allow you to “tell” the scanner which case it is dealing with.
When calculating color correction, the color shift limits set in memory are used on each of the color axes (Y-B, M-G, C-R plus additional axes for incandescent and fluorescent lamps), above which the correction is not applied (the presence of a natural color dominant is assumed). The degree of correction is determined by the maximum value specified in memory (Color Correction Factor) and the amount of deviation from the “gray center”. It is maximum at small deviations and decreases linearly to zero as it approaches the established limits. The balance of the “gray center” is individual for each film. The memory stores the average density of the normal negative and the mask for each configured film channel according to the DX code. Statistics are kept on these values, and the specified values can be refined over time using statistical data. When calculating the density and color deviation of each frame, the measured integral density is compared with the density of a normal negative, taking into account the mask deviation.
The scanner shows acceptable results when operating in automatic mode. Errors in density average 5-10%. Here are typical cases of errors. When offset from the center until it touches the edge of the frame of a foreground subject shot with flash, the scanner can assign the scene to the Back Light group, instead of Flash-1, and apply correction with the opposite sign. Human faces in a group photo may be too small for the scanner to detect. It will not apply the correction provided for the Flash-2 plot, and they will appear too light on the print. A scene containing white objects shot in evening or yellow-red artificial lighting (ship, building) can be classified by the scanner as Flash-2. In this case, the printer will print too dense, bringing white objects to the normal density of a human face. Often the scanner will try to normalize a light-colored shirt, mistaking it for the main foreground object (Flash-1). It is clear that the portrait turns out to be too dark. Significant color shifts caused by improper processing and storage of the film are almost not corrected. It is impossible to avoid some color distortion if there are small color dominants in the plot. In manual printing, an experienced operator can anticipate some of the situations mentioned and try to correct them. Optimizing the operation of the scanner algorithm is the process of finding a compromise by adjusting the parameters of the same name in memory, which are responsible for the degree of correction of each of the subject groups. Also, a compromise between the print quality of scenes with color dominants and the correction of unwanted color shifts is the adjustment of the correction limit values and CCF.
Shows the best results with automatic printing TFS scanner printer families Agfa MSC. “Total Film Scanning” technology allows you to print all products in a channel common to all films with minimal operator intervention (only film loading). Even films with serious deviations due to violations of the processing and storage process are corrected quite satisfactorily. The procedure for setting up the printer is extremely simple. Let's try to figure out how this simplicity is achieved. The “eyes” of the scanner consist of three lines of 16 photosensitive elements, each of which is exposed to one of the main spectral components of light, as well as an additional line for analyzing the density of the negative ( Fig.2). The scanner filter block has characteristics adapted to the spectral sensitivity of the emulsion of the type of photographic paper used, and is made in the form of a replaceable clip. This allows the scanner to see the negative through the “eyes” of the photo paper. There are no moving parts - scanning occurs as the film is fed. When scanning a full frame of 135-format film, the computer obtains a 16x31-dot array of data for each of the three primary colors. When you load film, it is completely scanned. The data collected from the entire film is analyzed by the scanner's algorithm, and the identified features are taken into account, along with information about each frame. The information obtained is sufficient for the algorithm to correctly calculate not only the correction associated with the characteristics of the films different types and manufacturers, but also compensated for color shifts of films with various deviations from the norm. Classification of individual frames into subject groups is carried out similar to what happens in a scanner Gretag, but with a more reliable result, due to both the higher resolution and information about other frames of the film. The algorithm’s performance with scenes containing a dominant color is noteworthy. When calculating the color correction of an individual frame, the algorithm ignores areas with increased color shift, which makes it possible to obtain an undistorted color rendition of an object in a scene with a dominant color.
Setting the scanner parameters DL1, DL2, DL3, stored in the printer’s memory, allows you to optimize the scanner’s recognition and correction of specific shooting conditions. For example, if you notice that prints from high-contrast negatives containing a foreground subject taken with flash are underexposed, you should increase the DL1 setting slightly. The DL2 parameter is responsible for recognizing and correcting contrasting scenes with a bright background. As is the case with Gretag optimizing these parameters is a search for some compromise. Correction of negatives with low contrast, as well as scenes against the backdrop of large water surfaces, snowy landscapes, etc., is done by adjusting the DL3 parameter.
By correctly setting these parameters and adjusting the threshold for recognizing color dominants, the operator’s work in automatic printing mode becomes extremely simple and convenient, even if the film contains frames with significant deviations from normal exposure conditions.
Concluding a comparative review of the principles of operation of ML scanners and their ability to correct the density and color of photo prints, I would like to note that even the best scanner, equipped with a good algorithm, is not able to compensate for serious deviations in the technological parameters of film and paper processing processes from normal ones. In other words, you should always remember that the corrective work of the scanner is most effective provided that both the film processor and the paper processor are operating normally, from a chemical point of view.
Igor GORYUNOV, Pavel ZAKHAROV
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Descriptions of mini-photo laboratories
A periodically updated section of the site dedicated to descriptions, first of all, of new, and also, whenever possible, old models of mini-photo laboratories.
Tikhon Baranov
Desktop scanners appeared in the 80s and immediately became the object of increased attention, but the complexity of use, the lack of a universal software, and most importantly, the high price did not allow the scanners to go beyond specialized use.
Not much time has passed since then, but a whole line of desktop scanners has already emerged, intended mainly for office and home use. Moreover, over the past few years, thanks to incredible price reductions, the popularity of scanners has grown significantly. The price of a good flatbed scanner today is comparable to the price of a good video card or printer, so it is logical to continue purchasing a computer and printer by purchasing a scanner.
Over the past two years, flatbed scanners have dropped so much in price, and the range of models offered has grown so much, that choosing this device for specific tasks has become more than relevant.
In the proposed material I would like to talk about the structure of a flatbed scanner, analyze the features of the scanning process and give some recommendations for purchasing a flatbed scanner.
A desktop scanner is indispensable when working with a computer if you need to make inserts graphic images or texts from paper into documents created using a computer. Modern desktop scanners are quite easy to use and have an intuitive interface, but there are a number of characteristics and features that you should pay attention to when choosing a scanner - the optical system, the TWAIN module software and the interface. Let's look at all three parts separately.
Optics and mechanics
This part consists of a scanning carriage with a light source, a focusing lens or lens, a charge-coupled device and an analog-to-digital converter (ADC).
Actually, the entire scanning process involving all of the above looks like this. The image (text, graphics, photograph) to be scanned is placed face down on the transparent glass under the scanner lid. Then the carriage begins to move, making a path equal to the length of the glass. A cold cathode lamp placed on it illuminates the image. Using a focusing lens, the luminous flux from the image is projected onto a charge-coupled device, where it is converted into analog information. The latter in the ADC becomes digital, i.e. bit, and thus understandable to the computer. A similar analog-to-digital (and vice versa) conversion is performed by the modem, since information is transmitted over telephone lines in analog form.
Accurate color reproduction when scanning color images occurs by dividing the scanned color into three main components - colors: red, green and blue.
Here I would like to say a few words about the concept of “color depth”, since if color information is stored in bits, then color depth is a certain number of bits. The standard (“true”) color depth can be considered to be 24 bits per pixel, when RGB colors accounts for 8 bits. Accordingly, with this bit depth, the scanner perceives 16.77 million color shades of one point. In addition to 24-bit scanners, 30-, 36-, 42- and even 48-bit scanners are widely used today. But what’s interesting: the human eye is “not designed” for a color depth of more than 24 bits. The increase in the bit capacity of scanners is not caused by the desire of manufacturers to make extra money on the hysteria around technological races, the reason is different: analog-to-digital conversion leads to the appearance of distortions in the lowest, most “vulnerable” bits - 30-bit (and higher) systems do not allow empty information to pass through computer, “pulling” the output color depth to full 24 bits.
Previously, color scanning had to use three-pass technology. That is, the first pass with a red filter to obtain the red component, the second - for the green component and the third = - for the blue. This method has two significant drawbacks: low speed and the problem of combining three separate scans into one, with the resulting color mismatch.
The solution was the creation of True Color CCD, which allows one to perceive all three color components of a color image in one pass. True Color CCD is standard on this moment and no one in the world produces three-pass scanners anymore. Similarly, at one time black and white flatbed scanners ceased to exist.
The average user may get confused by the variety of different resolutions that the manufacturer offers us. This concept can be divided into two groups:
- Optical resolution
Determined by the number of cells in a matrix line divided by the width of the scanning field. Typically, the scanner resolution is indicated by two numbers: 300x600 ppi, 600x1200 ppi, etc. I would like the reader to note that the designation ppi (pixels per inch) is more accurate in relation to the scanning resolution, in relation to the image printed on a printer - dpi (dots per inch).
- Interpolated Resolution
Selected by the user and can be several times higher than the actual scanner resolution. For example, the software resolution of 600 ppi of the HP ScanJet 5100C scanner can be increased to 1200 ppi. However, more does not mean better in this case. High-quality scanning is obtained with a resolution equal to optical, or lower, but a multiple of it. Manufacturers of desktop scanners are very fond of this characteristic, often including it in the name and putting it in large letters on the colorful box. You can see 4800, 9600, etc.
When purchasing a scanner, you should understand that the general approach in computer technology “the more the better” (memory, processor frequency, etc.) generally does not apply to scanners. That is, of course, it’s better and of course more expensive, but you may never need it! The resolution you need to use when scanning is determined by the output device you are using.
When scanning images, you need to rely on the optical resolution of the scanner. Those. If the scanner has a resolution of 300x600 ppi, scan in 300x300 ppi or 150x150 ppi mode. Files with interpolated resolution (in this case it can be 600, 1200, 2400 or more ppi) are not only large in volume, but also contain many unreal, programmatically “invented” pixels, which affects the quality of the resulting image.
For one-to-one display on the screen (presentations, Web design), it is enough to set 72 dpi or 100 dpi, since all monitors produce either 72 or 96 dpi.
When using an inkjet printer when outputting color images, it is enough to set the scanner resolution = printer resolution/3, since printer manufacturers indicate the maximum printer resolution when printing in color inkjet printers use three points to create one point obtained from the scanner. That is, here, too, 200 - 250 dots per inch will be enough for you.
Then in what cases is it necessary high resolution? The answer is simple: if you need to enlarge or stretch an image taken from the original. Think about it: maybe you will never have such a need, but you will have to overpay quite a lot.
One of the main characteristics of a scanner is dynamic range. Let us explain this characteristic a little. Any image has an optical density: from 0.0 D (absolutely white, transparent) to 4.0 (absolutely black, opaque). The dynamic range of a scanner is determined by its ability to perceive the optical density of the scanned image. If the scanner has a dynamic range of 2.5 D, then it will be able to cope with photographs, but will fail when working with negatives having an optical density of more than 3.0 D. This means that the scanner will not perceive the darkest areas of the image and will produce incomplete scanning. To make it clear, I will give, as an example, Soviet color photographic film. Anyone who has dealt with her will understand the comparison perfectly. Soviet photographic film was produced with a low color depth and therefore had great problems with displaying light and dark tones.
Cheap flatbed scanners have a dynamic range of 2.0 - 2.7D, good ones 3.0 = - 3.3D, latest models 3.6D.
One of the most important parameters of the matrix is the level of noise it produces. High level"noise" has an extremely negative effect on the quality of scanning, reducing the dynamic range and the number of bits with truly useful data. The permissible noise level of CCD matrices of SOHO sector scanners is 3-4mV.
In this article, the author tries to give some overview of scanners with traditional CCD technology. To be fair, it must be said that there is an alternative on the market - CIS technology. The latter has been known for quite a long time, but scanners using this technology have appeared relatively recently. Such scanners completely lack optics and mirrors; the receiving element is equal in width to the working scanning field and is a line of several identical matrices. In addition to other relatively minor disadvantages, this option has two fundamental ones: poor focusing (no optics) and small gaps between adjacent matrices. This does not interfere with text scanning, but for working with full-color graphics it is better to choose a scanner built on the basis of traditional CCD technology.
TWAIN module
Paradoxical but true: the scanner is not standard device for Windows. (One could dispute this statement, since drivers for scanners are installed in Windows'98. However, I have not yet come across a scanner that would work with the Ninety-Eight drivers. Perhaps because the drivers are written for USB, and scanners with this there are still few interfaces on the market.) For the interaction of computer graphic applications and the scanner's optical-electronic system, it is necessary special program, which is played by the TWAIN module. It is not particularly complicated, but we must take into account the fact that different versions of the TWAIN module from the same manufacturer may behave inappropriately in relation to different versions Windows, up to their complete incompatibility. This can be easily understood if we take into account the similarity of the TWAIN module to an ordinary driver that is subject to updating, for example, with the release of a new “brainchild” of Bill Gates. Actually, thanks to the TWAIN module, the user is able to control the scanning process on the monitor screen. These modules, like “works of art” from specific scanner manufacturers, are distinguished by a different set of their functionality. In the modules of inexpensive color tablets, the user will most likely find such functions as: a preview window, automatic detection scanning area, the ability to select resolution and scanning mode, adjust contrast, brightness and gamma, printed raster suppression filter, etc. In addition to those mentioned, there are many other, more specific, functions - they can be found in modules of professional scanners, we will not name them here .
Hardware interface
The interface affects the speed of the scanning process, being responsible for the speed of data exchange between the computer and the scanner. Now LPT and SCSI scanners have been supplemented by models equipped with a promising and fast USB interface. For example, there are three varieties of the Astra 1220 model (manufactured by UMAX): Astra 1220P, connected to the printer port, Astra 1220U, using the USB interface, and Astra 1220S = - SCSI device. The fastest of them is the model with SCSI interface, with USB it is slower, and with LPT it is the slowest. In general, the SCSI/USB/LPT ratio is considered to be 3/2/1. At the same time, it should be noted that in in some cases The speed performance of scanners with a particular interface may differ significantly from expected. However, such moments only confirm the rule, so the price difference between LPT, USB and SCSI scanners is completely justified.
However, there are a number of conditions, the fulfillment of which can somewhat speed up the operation of the interface devices of your scanner.
There are known cases where a conflict between two SCSI controllers led to a significant slowdown in the scanner's operation. If this problem cannot be solved by reassigning resources to conflicting devices, consider installing the scanner as part of a SCSI chain on a more powerful controller. In this case, the scanner must be the last device in the chain, it must be terminated, and the SCSI ID must be set to a position that meets the requirements of the controller being used (valid positions: 1...6). Our experience of using Mustek scanners with high-speed Adaptec 2940 AU and Asus SC-200 PCI controllers shows that the scanner connected in this way works faster than with the “native” SCSI-II card DTC3181.
Scanner selection
First of all, I would like the buyer to keep in mind that a scanner is always bought for specific work, and do not try to twiddle your fingers here in front of your friends, showing them the model that you purchased, well, with very cool characteristics - an experienced, knowledgeable user can over you laugh. If you have no idea what kind of work you will be doing, then you most likely need a scanner for your home, and below we will select a scanner for you.
Text scanning work
Any scanners are suitable for this work, since black and white text can be scanned well by almost any scanner on the market - feel free to choose the cheapest option from one of the well-known manufacturers.
Homework
If you do not set yourself global, large-scale tasks and you do not have some kind of “super-duper-laser color” printer nearby, with “drop-dead” characteristics, with the help of which you quietly intend to do what our factory does "Goznak", then the Scan Express series from Mustek is suitable for you, with minimum price it will give you quite acceptable quality. To view images on a monitor, a scanner resolution of 100 dpi is enough; for printing on a printer with a slight increase, 600 dpi is enough. If you are going to create a huge home photo archive, then you should pay attention to more powerful models - the Mustek Paragon series, designed for large volumes of work, and Umax Astra scanners with improved color rendering, for those who are familiar with PhotoShop firsthand and can easily level to calibrate your monitor.
If you are not familiar with internal device computer - choose scanners with a connection to a parallel port - they are a little slower, but easier to install. If you are lucky enough to own a computer from the latest year with a USB bus, then a scanner on a USB v port will be more preferable for you - it is faster than a scanner on an LPT. For those who are not afraid to install a SCSI card themselves, scanners with a SCSI interface are best suited.
Office work
Scanners for the office should be designed for a large volume of work and better reproduce colors, since offices usually have higher quality color printers. The scanner should allow you to connect a slide adapter, preferably also connecting an automatic document feeder. The Paragon Mustek series is suitable for such work as entry-level scanners. To create and print your own colorful leaflets and presentations, you need scanners with better color rendering - Umax Astra and Agfa Snap-Scan (AGFA scanners provide greater capabilities to a trained operator). The most powerful scanner in this class is the Umax Astra 2400S Plus, designed for large volumes of work.
Hewlett-Packard scanners have become quite popular both around the world and in our market. For the most part, they are located in various offices of our country, having quite good intercity services and repair and maintenance workshops. The most popular models for office work are ScanJet 5200C and ScanJet 6200C
Scanners for advertising agencies
The main tasks for these scanners are high-quality scanning of small volumes of slides and paper originals. The scanner must have a high resolution (To scan slides and print them with a printed image format of 10x15 cm (standard photograph format), you will need a resolution of 1200 dpi, and to print a slide in A4 format - already 2400 dpi.), as well as good dynamic range. (For scanning photographs, a 2.3D range is required, for slides a range of optical densities greater than 2.8-3.0 D is required, and for negatives greater than 3.3 D.) The cheapest scanners in this class are the Agfa Duoscan T1200 with excellent quality, but low resolution 600x1200 dpi, and Mustek Paragon Power Pro with good resolution 1200x2400 dpi, but with a low dynamic range - for companies that cannot afford significant financial costs. For more demanding users, AGFA Duoscan and Umax PowerLook III, HP ScanJet 6350C scanners with good color rendering and dynamic range (3.4D) and high resolution (1000x2000 and 1200x2400, respectively) are suitable.
Scanning a large number of slides
To scan large volumes of slides, you need scanners with the same characteristics as the previous group, but in a larger format - A3. On the glass of such a scanner there are several slides at once, which are scanned in batch mode. If you do not need high scanner resolution, then the Mirage IIse scanner is the ideal choice for you in this group. The AGFA Duoscan T2000XL scanner with a high resolution of 2000x2000 dpi is suitable for you if you need to enlarge scanned slides to a format close to A4. Hewlett-Packard also has a pretty good offer on the market for this type of work, presenting its model on the market - Photo Scanner S20, which, according to the author, is well optimized for working with 35 mm negatives.
Scan large format slides
Scanning X-rays, flaw detection materials and aerial photography. Here are scanners with low resolution, but with good color rendering quality and high dynamic range. These are Mustek Paragon A3 Pro with a resolution of 600x1200 and Umax Mirage IIse with a resolution of 700x1400 dpi.
Scanners for Printing
For these tasks, scanners must have the highest performance, and the choice of scanner should be determined largely by the price you are willing to spend on it. The simplest scanner in this category is the AGFA Duoscan T2500 with a resolution of 2500 dpi. A more powerful model Umax PowerLook 3000 with a resolution of 3048x3048. And two AGFA A3 format models - AgfaScan 5000 with a resolution of 2500x5000 and AgfaScan XY-15 with a resolution of 5000x5000 in full A3+ format.
Finally, I would like to give some advice when purchasing this device:
And one more thing: when transporting the scanner, do not forget to put a special plug in closed mode, otherwise you will end up driving between the service center and your home.
That, it seems, is all for the first time. Yes, and the last thing: one of my friends has accumulated a bunch of different things at home computer hardware- video cards, processors, sound cards, - he sold it and bought himself a scanner. Dear reader, take a look in your closet, maybe there is your scanner that you haven’t purchased yet. So think, decide, search! The choice is yours.
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Do not be surprised if you do not find these words in the characteristics of your scanner - manufacturers do not always indicate this indicator. But this does not mean that this characteristic does not play a significant role in the quality of the resulting image. On the contrary, many experts agree that this is the main indicator of the quality of the scanner.
What is dynamic range?
More precisely, this parameter is called the optical density range.
Optical density is a metric that allows you to numerically measure how dark the original is. For a transparent original, optical density is the decimal logarithm of the ratio of the total light flux to the light flux passing through the original; for opaque ones - the ratio of the entire flux to the reflected light.
Thus, the darker the original, the greater its optical density. For example, an optical density value of 0.01 corresponds to almost white light, and values of 4.0 and higher correspond to almost black light, practically indistinguishable to the eye.
On any slide there are both light and dark areas - a whole range of different optical densities. The range between the smallest and largest optical density on a given original is called its dynamic range.
Scanner dynamic range
Not only the original has dynamic range, but also the scanner. The dynamic range of a scanner is the difference in optical densities that the scanner can detect.
All scanners recognize white color quite well. In other words, they have no problems with minimum optical density. For most scanners it is 0.01 or even less. Problems arise when scanning dark areas where there is very little light. Here everything depends on the sensitivity of the reading photocell: the more sensitive the CCD line, the better the scanner recognizes dark areas.
What does “recognize” mean?
This word means two actions at once. First, the scanner must distinguish between a dark shade and maximum black. Otherwise, many dark areas in the scanned image will appear as just a black spot without any detail. Secondly, the scanner must scan a dark area without noise - a kind of colored garbage in the form of multi-colored dots. After all, the darker the original, the weaker signal on the photocell, and the greater the contribution to the image will be made by the noise of the photocell itself and other electronic components of the scanner.
The scanner's ability to distinguish dark from black areas and the degree of noise in the dark areas are usually related. They are determined by the quality of the photocell and the color depth of the scanner: the darker areas the scanner recognizes, the less noise the photocell introduces.
Therefore, these two parameters are usually combined by one characteristic - dynamic range, which shows how high-quality the photocell is installed in the scanner, and therefore, how dark areas it recognizes and what level of noise in the shadows it produces when scanning. Of course, the higher the dynamic range value, the better.
In addition, dynamic range depends on the scanner's color depth, that is, the number of shades of gray (brightness) it can reproduce. This is natural: the fewer gradations of brightness the scanner transmits, the smaller the difference between the lightest and darkest shades that it recognizes.
These parameters are connected very simply. Let's say the scanner's color depth is 36 bits, or 12 bits per color. This means that it recognizes 4096 shades of gray. The decimal logarithm of 4096 gives 3.6 - this is the maximum dynamic range of this scanner. In reality it is less because the sensitivity of the photocell is not ideal. How much depends on the quality of the photocell. However, we can say for sure that the dynamic range of this scanner cannot exceed 3.6.
Dynamic range can accurately classify scanners (Table 1).
Original dynamic range
Obviously, the dynamic range of the scanner must exceed the dynamic range of the original. Otherwise, when scanning, some of the information from the original will be lost: if the image is not completely black, then the dark shades will disappear. For example, instead of a shadow, there will be just a black spot on the face. Or the scanner will increase the brightness of the image and recognize dark areas well, but instead of light areas you will get spots, this time white.
Data for the most common opaque originals is shown in Table 2.
Thus, the range of a scanner designed to scan exclusively opaque originals should be at least 2.3–2.5. On the other hand, it should not exceed these figures too much, since as the dynamic range increases, the price of the scanner increases exponentially.
With transparent originals the situation is somewhat more complicated. Firstly, photographic materials can be professional or amateur. The latter have a slightly smaller range of densities.
Secondly, unlike opaque originals, which are usually printed on white paper (that is, the dynamic range is measured from low-density white), in negatives the lightest shade still has significant density.
This means that when scanning negatives and slides, you need to take into account not only the dynamic range, but also the maximum optical density. For example, a slide with a dynamic range of 3.0 might have densities ranging from 0.7 to 3.7. But the dynamic range of the scanner is measured practically from white color - from low densities. So if the scanner's range is 3.5, then the maximum density it can recognize is 3.55 (the maximum is 3.6). Such a scanner will not be able to correctly scan the slide described above, although its dynamic range is higher than that of the original.
Therefore, for transparent originals it is better to take into account not the dynamic range, but the maximum optical density (Table 3). In other words, the maximum optical density of the slide must be less than the maximum density that the scanner can recognize.
What to scan with?
Whatever the manufacturer claims, the dynamic range of a flatbed scanner from the “office and home” class, the so-called SOHO, costing up to $450, does not exceed 2.6–2.7. The CCD line alone, capable of providing a dynamic range of 3.0, is more expensive.
This scanner handles opaque originals well, but dark areas on slides will look like a solid black spot with a lot of noise. If you try to scan a negative with such a scanner, then after inverting all the light areas (those that were dark on the negative), for example, the sky with clouds or a light shirt, will look like a solid white spot without any details, except for the same noise.
Therefore, even if you buy a slide module for $200 with your scanner, you won’t be able to scan slides and, especially, negatives with high quality.
The minimum dynamic range at which you can hope for a more or less decent result is 3.0, or better yet 3.4. The minimum cost of a flatbed scanner with this range is $600. A slide scanner with 3.0D will not cost much less, but for professional use scanners with a range of 3.4D and higher are needed.
What to scan?
We will not try to classify the originals, but will only figure out which originals should be preferred and which ones should be avoided, and why.
Let's start with the simplest thing - scanning text. High Definition It's not required for this job, but there are still subtleties.
Firstly, when choosing a scanning method, any scanner offers two options:
- mode black&white(halftone) - black and white without shades of gray;
- mode grayscale- with shades of gray.
In the first case, you can forget about the drawings. They will turn into black spots, leaving only the text. Moreover, if the text is not very clear, blurry in places or simply pale, then the resulting image will look deplorable.
On the other hand, black&white mode is the fastest and most economical in terms of file size. It should only be used for very clear text.
In other cases, it is better to prefer scanning in grayscale. A text recognition program will do an excellent job with such a file, and drawings, logos, etc. will be scanned normally.
If the original is in color, you need to take into account the capabilities of the scanner.
In principle, the most best original- a slide, a little worse - a negative, even worse - a photograph, and it is generally better to avoid printed color prints like magazine clippings.
Why?
Firstly, it is in this order that the dynamic range of the originals decreases. But this is not the main reason why a slide or negative is preferable to a photograph.
The fact is that each original is characterized by a color gamut - a set of transmitted shades. This parameter should not be confused with color depth. Color depth shows the number of shades, and color gamut shows what shades these are.
Let's illustrate this with an example. The human eye has the largest color gamut. It can be depicted in the form of a certain figure, which reflects all the perceived shades (see figure).
The large triangle outlines all the shades that the slide and film in general convey, the smaller triangle corresponds to the colors transmitted by the monitor (the outline for the scanner is something between the slide and the monitor). Finally, the inner figure corresponds to the CMYK ink set, that is, the color gamut of the printing press (and color laser printer, which has a slightly larger color gamut).
Thus, the green-blue gamut is well conveyed by photographic film and a scanner, but not by a printer (a well-known fact: a standard 4-color printer cannot depict a blue sky).
Hence the moral - if you have a choice, then you need to scan the original, which conveys a greater number of shades, that is, a slide, and not a photograph printed from it. However, not all scanners can scan slides - due to the weak dynamic range of office models. Therefore, the owner of a $100–200 scanner often simply has no choice.
Separate mention must be made about printed prints. Printers and printing machines print with special dots - a raster, the frequency of which is not too different from the resolution of the scanner 1. Do you want to know what happens if you superimpose two periodic structures - a scanner and a print - on top of each other? Look at the light through two layers of nylon or any other translucent synthetic fabric. You will see moire. The same moiré will result from scanning a printed print.
The special Descreen function in the scanner driver allows you to combat this effect. It removes moire, slightly blurring the image. But at the same time, quality suffers significantly. Therefore, you can scan magazine clippings only with subsequent reduction of the image, then the blurry effect will not be so noticeable.
Quick summary - if your scanner allows, scan slides, not photos. If possible, avoid scanning printed prints, and if there is no way out, then scan and then reduce the image by at least 1.5 times.
For office and home tasks, as well as for most work on computer graphics the so-called ones are best suited flatbed scanners. Various models of this type are more widely available on sale than others. Therefore, let's start by considering the principles of construction and operation of scanners of this particular type. Understanding these principles will provide a better understanding of the meaning technical characteristics, which are taken into account when choosing scanners.
A flatbed scanner is a rectangular plastic case with a lid. Under the cover there is a glass surface on which the original is placed to be scanned. Through this glass you can see some of the insides of the scanner. The scanner has a movable carriage on which a backlight lamp and a mirror system are installed. The carriage moves through the so-called stepper motor . The lamp light is reflected from the original and, through a system of mirrors and focusing lenses, enters the so-called matrix, consisting of sensors that produce electrical signals, the magnitude of which is determined by the intensity of the light incident on them. These sensors are based on light-sensitive elements called charge coupled devices(CCD, Couple Charged Device - CCD). More precisely, on the surface of the CCD a electric charge, proportional to the intensity of the incident light. Next, you just need to convert the value of this charge to another electrical quantity- voltage. Several CCDs are located side by side on one line.
The electrical signal at the output of the CCD is an analog quantity (i.e., its change is similar to the change in the input quantity - light intensity). Next, the analog signal is converted into digital form, followed by processing and transmission to a computer for further use. This function is performed by a special device called analog-to-digital converter(ADC, Analog-to-digital Converter - ADC). Thus, at each step of moving the carriage, the scanner reads one horizontal strip of the original, divided into discrete elements (pixels), the number of which is equal to the number of CCDs on the line. The entire scanned image consists of several such stripes.
Rice. 119. Diagram of the design and operation of a flatbed scanner based on a CCD (CCD): the lamp light is reflected from the original and, through an optical system, hits a matrix of photosensitive elements, and then to an analog-to-digital converter (ADC)
Color scanners now typically use a three-row CCD matrix and illuminate the original with calibrated white light. Each row of the matrix is designed to perceive one of the basic color components of light (red, green and blue). To separate colors, use either a prism that splits the beam white light for colored components, or a special CCD filter coating. However, there are color scanners with a single-row CCD matrix, in which the original is illuminated in turn by three lamps of basic colors. Single-row, triple-illuminated technology is considered obsolete.
Above we described the principles of construction and operation of so-called single-pass scanners, which scan the original in one carriage pass. However, three-pass scanners are still found, although no longer commercially produced. These are scanners with a single-row CCD matrix. In them, with each pass of the carriage along the original, one of the basic color filters is used: for each pass, information is removed on one of three color channels Images. This technology is also outdated.
In addition to CCD scanners based on a CCD matrix, there are CIS (Contact Image Sensor) scanners that use photocell technology.
Photosensitive matrices made using this technology perceive the reflected original sung directly through the scanner glass without using optical systems focusing. This made it possible to reduce the size and weight of flatbed scanners by more than half (down to 3-4 kg). However, such scanners are only good for extremely flat originals that fit tightly to the glass surface of the working field. In this case, the quality of the resulting image significantly depends on the presence of extraneous light sources (the CIS scanner cover must be closed during scanning). In the case of volumetric originals, the quality leaves much to be desired, while CCO scanners give good results for volumetric (up to several cm in depth) objects.
Flatbed scanners can be equipped with additional devices, such as a slide adapter, automatic document feeder, etc. Some models are provided with these devices, but others are not.
Slide adapter (Transparency Media Adapter, TMA) is a special attachment that allows you to scan transparent originals. Transparent materials are scanned using transmitted rather than reflected light. In other words, the transparent original must be between the light source and the photosensitive elements. The slide adapter is a mounted module equipped with a lamp that moves synchronously with the scanner carriage. Sometimes they simply illuminate a certain area of the working field evenly so as not to move the lamp. Thus, the main purpose of using a slide adapter is to change the position of the light source.
If you have a digital camera (digital camera), then you most likely do not need a slide adapter.
If you scan transparent originals without using a slide adapter, you need to understand that when the original is irradiated, the amounts of reflected and transmitted light are not equal to each other. So, the original will miss some of the incident color, which will then be reflected from the white coating of the scanner lid and pass through the original again. Some of the light will be reflected from the original. The ratio between the parts of transmitted and reflected light depends on the degree of transparency of the original area. Thus, the light-sensitive elements of the scanner matrix will receive light that has passed through the original twice, as well as light reflected from the original. The repeated passage of light through the original weakens it, and the interaction of the reflected and transmitted beams of light (interference) causes distortion and side video effects.
An automatic feeder is a device that feeds originals into the scanner, which is very convenient to use when streaming images of the same type (when you do not need to frequently reconfigure the scanner), for example, texts or drawings of approximately the same quality.
In addition to flatbed ones, there are other types of scanners: manual, sheet-fed, drum, slide, for scanning barcodes, high-speed for streaming documents.
Handheld Scanner is a portable scanner in which scanning is carried out by manually moving it over the original. The principle of operation of such a scanner is similar to that of a tablet scanner. The width of the scanning area is no more than 15 cm. The first scanners for widespread use went on sale in the 80s of the 20th century. They were manual and allowed scanning of images in shades of gray. Nowadays such scanners are not easy to find.
Sheet or roller scanner(Sheetfed Scanner) - a scanner in which the original is pulled past a stationary linear CCD or CIS matrix; a type of such a scanner is a fax machine.
Drum scanner(Drum Scanner) - a scanner in which the original is fixed on a rotating drum, and photomultipliers are used for scanning. In this case, a dot area of the image is scanned, and the scanning head moves along the drum very close to the original.
Slide scanner(Film-scanner) is a type of flatbed scanner designed for scanning transparent materials (slides, negative films, X-rays, etc.). Usually the size of such originals is fixed. Note that some flatbed scanners have a special attachment (slide adapter) designed for scanning transparent materials (see above).
Barcode Scanner(Bar-code Scanner) - a scanner designed for scanning product barcodes. Its operating principle is similar to hand scanner and connects to a computer or a specialized trading system. If you have the appropriate software, any scanner can recognize barcodes.
High-speed scanner for working with documents(Document Scanner) is a type of sheet-fed scanner designed for high-performance multi-page input. Scanners can be equipped with input and output trays with a capacity of over 1000 sheets and input information at speeds in excess of 100 sheets per minute. Some models of this class provide two-sided (duplex) scanning, backlighting the original in different colors to cut out the colored background, compensation for background heterogeneity, and have modules for dynamic processing of different types of originals.
So, it is best suited for home and office flatbed scanner. If you want to do graphic design, then it is better to choose a CCD scanner (based on a CCD matrix), since it allows you to scan three-dimensional objects. If you plan to scan slides and other transparent materials, you should choose a scanner that has a slide adapter. Usually the scanner itself and the slide adapter that goes with it are sold separately. If you cannot purchase a slide adapter at the same time as the scanner, you can do so later if necessary. It is also necessary to determine the maximum sizes of scanned images. Currently, the standard format is A4, corresponding to a regular sheet of writing paper. Most household scanners are designed specifically for this format. Scanning drawings and other design documents typically requires A3 size, which corresponds to two A4 sheets joined along the long side. Currently, the prices of scanners of the same type for A4 and A3 formats are getting closer. It can be assumed that originals that do not exceed the A4 format will be better processed by a scanner oriented to the A3 format.
The parameters listed above do not exhaust the entire list, but at this stage In our consideration, we can only use them for now. When choosing a scanner, three aspects are decisive: a hardware interface(connection method), optical-electronic system And software interface c (the so-called TWAIN module). Next we will look at them in more detail.
With the advent of digital cameras, this task has become indecently simplified. It is no longer necessary to develop, print and even scan, even the most budget models Be sure to write the shooting date in EXIF, and non-budget ones also write the location coordinates - all that remains is to copy the files from the memory card and use any viewer program you like. What if you had several generations of photographers in your family, even amateurs?
This article will discuss what to do with old negatives, slides and prints. I note that I did not open America and any more or less qualified user can easily do all this himself.
1. Equipment
Purchasing a professional film scanner was not part of the author’s plans: in addition to negatives and slides, the archive contained about 4,000 photographic prints, which require a flatbed scanner, ideally with automatic feed. Of course, it is better to scan the original negative than the positive printed from it, but it was impossible to figure out for which photographs the negatives were preserved. Toad and common sense did not allow me to buy two scanners for what was essentially a one-time job.
As a result, for 5990 rubles. I purchased a mid-range Epson Perfection V350 Photo flatbed scanner equipped with an AFL (Auto Film Loader). Optical resolution of 4800 DPI allows you to scan negatives and slides. Of course, the dynamic range for this money is not the same as that of professional film scanners, and the speed leaves much to be desired, but...
In addition to the scanner, you will need a photo tank for washing old 35 mm films and a couple of clothespins for subsequent drying. You still need disk space: ~9000 photos scanned in adequate resolution (JPG maximum quality) took 45 GB from the author. If someone decides to store data in a loseless format (TIFF/PSD/etc.), then even more.
2. Software
4. Background correction. In meaning, this is analogous to Levels correction in Adobe Photoshop. It works well, some frames can be “extracted” immediately at the scanning stage. The “high” level is almost never used: if the frame is initially dark, trying to apply a filter will reduce the contrast to unacceptable levels.
5. Removal of defects. The most controversial filter. In pictures with a large number of uniformly filled areas (sky, calm water, furniture) it really allows you to remove a large number of defects. In photographs with a large number of faces of a small size relative to the frame area (group portraits, demonstrations), parts of the face may be mistaken for a defect, with all that it implies. He especially doesn't like the eyes :) The filter is resource-intensive and increases scanning time.
Sync Picasa Web Albums and Disk Catalog
After the first files from the scanner appear in the directory, you need to set up synchronization with Picasa web albums. In the album properties, select “Enable synchronization”:
After turning on the synchronization mode, do not forget to specify the size of the photos. For Reserve copy need to install " Images in original size" This will not affect the viewing speed, but it will greatly affect the synchronization speed (depending on your Internet connection speed). You can also turn on the “ private"if you don't want (I, for example, don't want:) for your photos to be publicly available. In “private” mode, you can grant viewing and editing access rights to the ones you select. Google users(Google account required).
That's all. Now, if you have the desire and time, you can digitize everything that was filmed in the pre-digital era. The scanner scans, Picasa automatically uploads photos to the web, and you don't forget to do it from time to time. backups to other media.
Don't forget about backup!
Additional Information:
- : A wonderful resource with articles on film scanning.
- in the same place: “Why you shouldn’t scan films on a tablet” (I completely agree, but...)
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