Tikhon Baranov
Desktop scanners appeared in the 80s and immediately became the object of increased attention, but the complexity of use, the lack of universal software, and most importantly, the high price did not allow 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 have 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 depth 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 resolution of printers; when printing in color, inkjet printers use three dots to create one dot received 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 the 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, because drivers for scanners are installed in Windows'98. However, I have not yet come across a scanner that would work with the drivers of the "ninety-eight". Perhaps because the drivers are written for USB, and scanners with this There are still few interfaces on the market.) For the interaction of graphical applications on a computer and optical-electronic system scanner required 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 “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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At first glance, the idea of creating a flatbed scanner with an optical resolution of more than 600 ppi, which is not designed to work with transparent originals, seems rather dubious - after all, for the vast majority of originals scanned in reflected light, 300-400 ppi is more than enough. However, we should not forget that a significant proportion of the originals scanned both at home and in the office are images printed using the printing method. Due to interference phenomena that occur when digitizing rasterized images, noticeable moire appears on the resulting image, which is quite difficult to combat without compromising the quality or size of the image. To combat such phenomena, special algorithms embedded in scanning control programs are used. As a rule, the moire suppression function works by scanning the original at an excessive (that is, greater than user-specified) resolution and then software processing the resulting image. This is where the advantage of high-resolution scanners will be obvious in the truest sense of the word.
Main technical parameters of scanners
Resolution
Resolution, or resolution, is one of the most important parameters characterizing the capabilities of a scanner. The most common unit of measurement for scanner resolution is number of pixels per inch (pixels per inch, ppi). Ppi should not be equated with the more well-known unit dpi (dots per inch- number of dots per inch), which is used to measure the resolution of raster printing devices and has a slightly different meaning.
Distinguish optical And interpolated permission. The optical resolution can be calculated by dividing the number of photosensitive elements in the scanning array by the width of the tablet. It is easy to calculate that the number of photosensitive elements in the scanners we are considering, which have an optical resolution of 1200 ppi and a Legal tablet format (that is, a width of 8.5 inches, or 216 mm), should be at least 11 thousand.
Speaking about a scanner as an abstract digital device, you need to understand that optical resolution is sampling frequency, only in this case the countdown is not based on time, but on distance.
In table 1 shows the required resolution values for solving the most common problems. As you can see, when scanning in reflected light, a resolution of 300 ppi is sufficient in most cases, and higher values are required either to scale the original to a larger size, or to work with transparent originals, in particular with 35 mm transparencies and negatives.
Table 1. Resolution values for solving the most common problems
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Application |
Required resolution, ppi |
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Reflected light scanning |
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Illustrations for Web pages |
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Text recognising |
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Line art for printing on a monochrome printer |
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Black and white photo for printing on a monochrome printer |
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Color photo for printing on inkjet printer |
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Text and graphics for faxing |
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Color photo for offset printing |
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Transmitted light scanning |
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35mm film, photo for web pages |
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35mm film, photo for printing on an inkjet printer |
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60mm film, photo for web pages |
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60mm film, photo for printing on an inkjet printer |
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Many manufacturers, in an effort to attract buyers, indicate in the documentation and on the boxes of their products an optical resolution value of 1200 * 2400 ppi. However, a figure twice as large for the vertical axis means nothing more than scanning with half a vertical step and further software interpolation, so in this case the optical resolution of these models actually remains equal to the first figure.
Interpolated resolution is an increase in the number of pixels in a scanned image through software processing. The interpolated resolution can be many times greater than the optical resolution, but remember that the amount of information obtained from the original will be the same as when scanning with optical resolution. In other words, it will not be possible to increase image detail when scanning at a resolution exceeding optical.
Bit depth
Bit depth, or color depth, determines maximum number values that a pixel color can take. In other words, the higher the bit depth when scanning, the greater the number of shades the resulting image can contain. For example, when scanning a black and white image with 8 bits, we can get 256 shades of gray (2 8 = 256), and using 10 bits we can get 1024 shades (2 10 = 1024). For color images, there are two options for the indicated bit depth - the number of bits for each of the basic colors or the total number of bits. The current standard for storing and transmitting full-color images (such as photographs) is 24-bit color. Since when scanning color originals the image is formed according to the additive principle from three basic colors, each of them has 8 bits, and the number of possible shades is slightly more than 16.7 million (2 24 = 16,777,216). Many scanners use a higher bit depth - 12, 14 or 16 bits per color (the total bit depth is 36, 42 or 48 bits, respectively), but for recording and further processing of images this function must be supported by the used software; otherwise, the resulting image will be written to a 24-bit file.
It should be noted that higher bit depth does not always mean higher image quality. When indicating 36- or 48-bit color depth in documentation or promotional materials, manufacturers often remain silent about the fact that some of the bits are used to store service information.
Dynamic range (maximum optical density)
As you know, darker areas of an image absorb more light falling on them than lighter areas. The optical density value indicates how dark a given area of the image is and, therefore, how much light is absorbed and how much is reflected (or passed through in the case of a transparent original). Typically, density is measured for a standard light source that has a predetermined spectrum. The density value is calculated using the formula:
where D is the density value, R is the reflectance coefficient (that is, the proportion of reflected or transmitted light).
For example, for a section of the original that reflects (transmits) 15% of the light incident on it, the density value will be log(1/0.15) = 0.8239.
The higher the maximum perceived density, the more dynamic range of this device. Theoretically, the dynamic range is limited by the bit depth used. Thus, an eight-bit monochrome image can have up to 256 gradations, that is, the minimum reproducible shade will be 1/256 (0.39%), therefore the dynamic range will be equal to log(256) = 2.4. For a 10-bit image it will be slightly more than 3, and for a 12-bit image it will be 3.61.
Essentially, this means that a scanner with a higher dynamic range can better reproduce dark areas of images or simply dark images (such as overexposed photographs). It should be noted that in real conditions the dynamic range is less than the above values due to the influence of noise and crosstalk.
In most cases, the density of opaque originals scanned for reflection is less than 2.0 (which corresponds to an area of one percent reflection), and a typical value for high-quality printed originals is 1.6. Slides and negatives may have areas of density greater than 2.0.
Light source
The light source used in the design of a particular scanner greatly affects the quality of the resulting image. There are currently four types of light sources in use:
- Xenon gas discharge lamps. They are distinguished by extremely short switching times, high radiation stability, small sizes and long service life. But they are not very efficient in terms of the ratio of the amount of energy consumed and the intensity of the luminous flux, have an imperfect spectrum (which can cause a violation of color accuracy) and require high voltage (about 2 kV).
- Fluorescent lamps hot cathode. These lamps have the highest efficiency, a very smooth spectrum (which can also be controlled within certain limits) and a short warm-up time (about 3-5 s). The negative aspects include not very stable characteristics, rather significant dimensions, a relatively short service life (about 1000 hours) and the need to keep the lamp constantly on while the scanner is operating.
- Cold cathode fluorescent lamps. Such lamps have a very long service life (from 5 to 10 thousand hours), low operating temperature, smooth spectrum (it should be noted that the design of some models of these lamps is optimized to increase the intensity of the luminous flux, which negatively affects the spectral characteristics). For the listed advantages, you have to pay for a rather long warm-up time (from 30 s to several minutes) and higher energy consumption than hot cathode lamps.
- Light emitting diodes (LED). They are usually used in CIS scanners. Color LEDs have very small dimensions, low power consumption and do not require time to warm up. In many cases, three-color LEDs are used, which change the color of the emitted light at high frequencies. However, LEDs have a rather low luminous flux (compared to lamps), which reduces scanning speed and increases the noise level in the image. A very uneven and limited radiation spectrum inevitably entails a deterioration in color rendering.
Scanning speed and warm-up time
During testing, the time required for a “cold” start and recovery from power saving mode was measured.
To evaluate the performance of the tested scanners, we measured the time required to complete several of the most common tasks. The countdown began from the moment you pressed the Scan (or similar) button in the application from which the scan was made, and ended after this application was again ready for work (that is, it was possible to perform any actions, such as changing settings or scanning areas).
2.6 Technical data
1) Resolution
Resolution tells us how many pixels or dots per inch can be captured and is expressed in ppi (pixels per inch) or dpi (dots per inch). The more pixels or dots are captured, the higher the detail in the scanned image. A resolution of 300 x 300 dpi corresponds to a total of 90,000 dots in an area of one square inch.
Optical resolution
Optical resolution depends on the number of photocells on the photosensitive element (horizontal optical resolution) and on the step size of the carriage motor that moves the photosensitive element across the document (vertical optical resolution).
2.7 Interpolated resolution
Whereas optical resolution can be achieved by hardware, interpolated resolution is achieved by scanner software. Through algorithms, the software creates additional (virtual) pixels between the real pixels captured by the photosensitive element, thus achieving the highest possible resolution. These additional pixels are the average color and brightness values obtained from adjacent pixels. Because these extra pixels do not actually represent the document being scanned, they are less accurate and do not enhance image quality. Therefore, in terms of image quality for a scanner, the optical resolution value is more important.
Sometimes, however, interpolation is important when the horizontal optical resolution, which depends on the number of photocells on the photosensitive element, is limited. For example, if the scanner were operating at an optical resolution of 300 x 600 dpi, the scanned image would be distorted because the horizontal optical resolution is lower than the vertical optical resolution. In this case, the optical resolution must be interpolated to achieve 600 x 600 dpi.
2) Color depth
Color depth, also called bit depth, indicates how many colors can be represented in a pixel. It depends on the sensitivity of the AD converter. An AD converter that uses 8 bit signals can represent 2(8) = 256 brightness levels for each color (red, green, blue) for a total of 2(24) = 16.7 million colors. In this case we have a color depth of 24 bits.
Internal and external color depth
Some scanners vary in internal and external color depth. The internal color depth indicates how many colors can be represented by the AD converter. External color depth indicates how many colors the scanner can actually render to the computer. The external color depth may be lower than the internal depth. In this case, the scanner selects the most appropriate colors and transmits them to the computer.
Color depth and quality
For scanning black and white documents, a color depth of 1 bit (0 or 1) is sufficient. Scanning color documents requires a much larger number of bits. Scanning a document at 24-bit color depth (16.7 million colors) results in near photographic quality, referred to as true color. Although at the moment most scanners on the market work with an internal and external color depth of 48 bits.
3) Optical density
Optical density is a measure of the opacity of an image area. It indicates the degree of light reflection of this zone. The darker area is a weaker reflection. The range from the brightest area (white) to the darkest area (black) in an image is the density range or dynamic range.
Optical density is measured with optical densitometers, and ranges from 0 to 4, where 0 is pure white (Dmin) and 4 is very black (Dmax).
With a narrow dynamic range, the scanner may not capture some of the image details and lose information. The brightest value that can be recorded is called Dmin, and the darkest value is Dmax. To get the best results, the scanner's dynamic range should include the dynamic range of the document that will be scanned.
In this case, the dynamic range of the scanner includes the dynamic range of the document so that numerous details in the white and black areas can be captured by the device.
The dynamic range of scanned originals varies from document to document.
As you can see from the table above, the scanner must have a particularly wide dynamic range to work with negatives or slides - these are the main properties inherent in photo scanners. The possible dynamic range of a scanner depends on several factors, such as the color depth of the AD converter, the purity of the lamp light and filters, and system interference (noise).
CCD or CIS: scanner technologies
There are two technologies of photosensitive elements:
3.1 CCD– a photosensitive element based on CCD (charge coupled devices). Typically, it is a strip of photosensitive elements.
As the carriage moves, light from the lamp is reflected from the scanned media and passing through a system of lenses and mirrors, hitting the light-sensitive elements that form a fragment of the image.
While moving, the carriage passes under the entire media, and the scanner compiles an overall picture from sequentially “photographed” fragments - an image of the media...
CCD scanner technology is quite old and, I must say, leading at the moment. It has the following positive aspects:
1) The CCD scanner provides greater depth of field. This means that even if you are scanning, say, a thick book, the binding area, which is usually difficult to press completely against the glass, will still be scanned with acceptable quality.
2) The CCD scanner provides greater sensitivity to color shades. Although many people call this argument “FOR” CCDs controversial, often CCD scanners actually recognize more colors than scanners of other competing technologies, which we will look at below.
3) CCD scanners have a long service life. Typically 10,000 hours.
Main disadvantages:
1. Greater sensitivity to mechanical influences (shocks, etc.).
2. Difficulty optical system may need calibration and/or cleaning of dust particles through certain time operation.
3.2 CIS (ContactImageSensor) – the photosensitive element is a line of identical photosensors, equal in width to the working scanning field, which directly perceive the light flux from the original. The optical system - mirrors, refractive prism, lens - is completely absent.
This is a fairly young technology that Canon is actively developing and promoting.
Main advantages:
1) The scanner turns out to be quite thin. Due to the lack of an optical system. The final product has a stylish design.
2) The scanner turns out to be cheap, because... CIS elements are cheap to produce.
3) Because in the CIS scanner, the mercury lamp is replaced by LEDs, we get several advantages: the absence of a separate power supply (the scanner receives power via a USB cable), constant readiness for work (no time is required to warm up the lamp - you can immediately start scanning after the user gives the command ); and a fairly high scanning speed (which again comes from the fact that the scanner does not need to heat the lamp).
4) The absence of the need for additional power from an outlet makes the scanner mobile: it is light in weight and compact in size, it can be carried with you along with a laptop; You can scan anytime, anywhere, even when your laptop is running on battery power.
5) CIS scanners are usually much quieter than CCD scanners.
6) It is believed that the absence of optics makes the CIS scanner less sensitive to external mechanical influences, i.e. it is more difficult to spoil it with careless handling. But you should also take into account that the tablet glass of such a scanner is often thinner than that of its competitor with optics.
Main disadvantages: CIS elements:
1) Due to the lack of an optical system, the photosensitive element has a shallow depth of field. Up to 10 times smaller than a CCD scanner. This means that scanning thick books is difficult because... The media should be pressed as tightly as possible against the glass.
2) The CIS scanner loses approximately 30% of its brightness after 500-700 hours of operation. Of course, usually for home use this is often not critical, but for those who scan often and a lot, this can be a decisive factor in their choice.
3) A CIS scanner, as a rule, has a smaller color gamut than a CCD, however, recently the gap between these technologies in color gamut is either insignificant or non-existent.
3D scanning
Currently, tacheometric surveying is widely used to solve construction and architectural problems, which makes it possible to obtain the coordinates of objects and then present them in graphical form. Tacheometric surveying allows measurements to be made with an accuracy of several millimeters, while the measurement speed of the tacheometer is no more than 2 measurements per second. This method is effective when shooting a sparse area unloaded with objects. The obvious disadvantages of this technology are the low speed of measurements and the ineffectiveness of surveying busy areas, such as the facades of buildings, factories with an area exceeding 2 hectares, as well as the low density of points per 1 m2.
One of the possible ways to solve these problems is the use of new modern research technologies, namely laser scanning.
Laser scanning is a technology that allows you to create a digital three-dimensional model of an object, representing it as a set of points with spatial coordinates. The technology is based on the use of new geodetic instruments - laser scanners that measure the coordinates of points on the surface of an object at a high speed of the order of several tens of thousands of points per second. The resulting set of points is called a “point cloud” and can subsequently be represented as a three-dimensional model of an object, a flat drawing, a set of sections, a surface, etc.
A more complete digital picture cannot be provided by any other known method. The shooting process is fully automated, and the operator’s participation is limited to preparing the scanner for work.
Hardware and software
Reading notes in near-computer periodicals devoted to the present and future of amateur photography, you involuntarily catch yourself thinking that the public is being systematically prepared for the solemn funeral of the traditional “film” process. There are no words, the successes of the digital camera industry are impressive, the speed of transferring footage to a computer for subsequent processing, the convenience and “eternity” of storing frames, the ability to save time and money on purchasing and developing films are more than powerful arguments. Cameras with a matrix having more than 2 Megapixels allow you to get frames that, when viewed on a monitor screen or printed on limited-size formats, evoke strong positive emotions. But...
For those who prefer to operate with absolute values, we recommend comparing three important indicators digital and analog photography.
Real Resolution standard (24x36 mm) frame of amateur color negative film ISO 100 is at the level of 100-110 pixels/mm (2550-2800 dpi) and thus there is an average of about 8.6-10.5 Megapixels per frame (with the “correct” exposure and “correct” development). Compare with 2-3.5 or more typical 1-1.5 Megapixels available on the market for amateur digital cameras.
Without going into the subtleties of the chemical reactions of color fixation in the emulsion, we note that in the general case, the image on film has color depth, exceeding 36 bits (> 68.7 billion shades). The vast majority of digital cameras provide a maximum color depth of up to 24 bits (> 16.7 million shades). The human eye is practically unable to see the difference between a 24 and 36-bit image, but any professional processing with subsequent printing requires 36 bits for correct conversions; in addition, a 24-bit image has limitations in displaying low-contrast details.
Important point- comparison cost a high-quality amateur digital model (a reasonable minimum with appropriate resolution - from $550-600) and a film camera (from $250).
Thus, digital amateur photography is still fatally behind analogue in terms of clarity, color accuracy and camera availability, although it is ahead of it in operational convenience, low overhead costs and the ability to edit using a computer.
The “computerized” amateur is faced with a dilemma - the quality of prints plus the low cost of the camera itself, or convenience plus low costs.
Fortunately, there is Alternative option, which combines some of the main advantages of both solutions. It's about film scanners(aka “film scanners”, slide scanners, etc.), allowing the owner of a film camera to transfer an image from a regular negative film or slide to HDD computer in digital form, suitable for further processing or storage as an “eternal” copy.
Film scanners - good and... different
It is clear that not every slide scanner will be a good purchase; models differ not only in workmanship (and price), but also in specific characteristics.
Format of negatives and slides , which can be digitized using specific model(35 mm, APS, etc.) is the first characteristic you should pay attention to. Regardless of the other advantages of the selected scanner, it will be useless if it does not support the format of the existing films.
Optical resolution
- one of the most important characteristics of a film scanner. As mentioned above, the resolution limit of amateur film is about 2800 dpi(professional - from 3150 and higher), therefore, the closer the scanner’s optical resolution is to this value, the less detail is lost during scanning. At the same time, higher values will not provide a noticeable advantage when processing amateur materials.
If digitization is carried out for subsequent output on a printer (with an optimal minimum print resolution of 300 dpi), then for printing on A4 format (with an increase of more than 8 times) you need to scan the original with a resolution of about 2400 dpi, A6 (or 10x15 cm) - 1200 dpi and so on.
Please note that for each format the minimum values are indicated - for output plot frame on full page A4 at the same 300 dpi will need more a high resolution.
Scanning for other purposes has its own requirements. Thus, the design of Internet pages does not require resolutions above 75 dpi, so for a frame that is supposed to be enlarged 4 times, scanning at only 300 dpi (with a corresponding reduction in file size) will be sufficient.
In addition to optical resolution, scanner characteristics often indicate significantly greater interpolation- obtained through mathematical processing of the scanned image (sometimes also due to a smaller step of movement of the scanning head). There are practically no serious improvements when using it with full-color originals, since the resolution of the light-receiving sensitive line remains the same, but the scanning time often increases many times over.
Optical Density Range
(dynamic range) is an extremely important parameter for fully scanning negatives and slides.
The very definition optical density refers to the scanned original, it characterizes the ratio of the original light flux to the light transmitted through the film (calculated as the decimal logarithm of this ratio). The minimum value of optical density is taken to be 0 (an absolutely transparent area, the incident light is equal to the transmitted light), and the maximum theoretically possible value is 4 (a very black area, practically no light transmitting).
Optical Density Range is defined as the difference between the minimum (always not 0 - usually from 0.1 and above) and maximum optical density (always not 4, usually less than 3.9-3.8) with which the scanner can work. In practice, the width of the optical density range for a slide scanner is its ability to capture low-contrast details in shadows/penumbra and in bright areas (the larger the range width, the more density gradations the scanner can separate and the more similar areas in density will be distinguishable). Using a model with a narrow dynamic range, you can only get an overly contrasty image, with “flat” shadows and brightly lit areas devoid of detail.
Let's explain with examples. If the scanner has a range specified 3.0D, then the maximum density of scanned areas other than black exceeds the minimum by 1000 times (with a corresponding number of intermediate gradations). Everything that lies beyond the upper border for the scanner is equivalent to black. Even if you increase the illumination, losses cannot be avoided - “the shadow will recede,” but the details of the areas with the lowest density will disappear.
A scanner with a 3.6D range is capable of more - the maximum density exceeds the minimum by 3980 times, and this is almost four times more gradations than the previous example. The scanned image becomes more voluminous, and the transitions of colors and penumbra are softer and more natural.
Currently minimum acceptable indicator for a slide scanner is considered 3.0D, good - 3.2D-3.4D, excellent - from 3.6D and higher.
The optical density range is strongly related to another characteristic of the scanner - color depth (bit depth)
.
As mentioned above, a 24-bit color representation could well be enough to view a photo, but for its subsequent high-quality processing and obtaining a wide working range of optical density, 36-bit is required (12 bits for each main RGB color or 12 bits per channel in Adobe Photoshop).
The dependence of the maximum achievable width of the optical density range on the color depth in a simplified form looks like this:
A 24-bit color representation (16.7 million colors) provides only 8 bits per color and 256 shades of gray, which roughly corresponds to 2.4D optical density bandwidth (256=10 to the power of 2.4).
30-bit (1.07 billion colors) - 10 bits per color, 1024 grayscale and about 3.0D.
36-bit (68.7 billion colors) - 12 bits per color, 4096 grayscale and about 3.6D.
Such maximums are not always achieved, since limitations are imposed by other factors (to achieve 3.6D, the entire chain from a high-quality readout matrix and ADC unit to the interface must support the processing and transmission of 36-bit USEFUL color information, free from noise and interference) .
The name of the characteristic often refers to “external” or “internal”. A significantly higher bit depth (for example, 40 bits) can be used inside the scanner, which is required to compensate for matrix noise and other operations that occur with losses. What is important for the user is the output characteristics of the scanner - what he receives in explicit form. At the same time, increased internal bit depth in most cases expands the range of optical densities processed by the scanner.
Internal noise of the matrix - a characteristic that is almost never indicated in the passport data of amateur scanners, but can be approximately assessed in practice (in a showroom, etc.) or found out from those who have already dealt with the selected model. In practice, the inherent noise of a slide scanner matrix appears when scanning areas with the highest density in the form of colored “garbage”, which deteriorates the overall image quality (the naturalness of shadows on slides and the purity of bright areas on negatives). The best (and most often expensive) scanners use high-quality matrices, analog-to-digital converters, and special algorithms for suppressing and filtering noise (unfortunately, amateur models have not yet reached the level of cooling (lowering the temperature) of the matrix used in astronomy). In addition, it can also be applied special methods noise reduction.
Focus depth range
- another parameter that is almost never explicitly indicated in the output of an amateur scanner, but is very important when scanning slides. If the distance to the negative emulsion can be set quite clearly by the feeding mechanism, then in the case of a slide the situation is more complicated - the thickness of the frame is rarely exactly equal to the standard one, and noticeable deformation of the film is possible due to the stresses that arise during fastening in the frame. The result is that a scanner with a narrow focusing depth range cannot provide sharpness across the entire frame or is even completely unable to digitize a slide with acceptable clarity.
The narrow range of focusing depth can be compensated by the presence of adjustment (semi-automatic or manual) or special devices for scanning slides removed from the frames.
Scan speed - a parameter that is of little importance when scanning individual frames, but is very important if several films are to be processed at once. Fast scanners are capable of processing one frame in 20-30 s, but as a rule only in the “Normal” or “Standard” mode (at the same time, scanning one film with 36 frames takes from 25 to 40 minutes, including the actions of changing sections of negatives and possible selecting settings for individual frames). The use of special modes can increase the scanning time of one frame many times over - up to 3-8 minutes (1.5-5 hours on 36-frame film, including the actions of changing negative sections and possibly selecting settings for frames). From the point of view of time consumption, the sequence of frame processing, the ability to process several frames simultaneously, etc., become especially important.
Interface - a characteristic that largely determines the speed of loading the resulting image onto a computer and the ease of connecting a slide scanner. The fastest interface used in slide scanners was and remains SCSI (requires a SCSI controller and a special cable in the kit or in the PC), the next fastest is the newer USB (requires a controller and USB ports, in addition to the relatively high speed transmission also provides a “hot” connection - without rebooting the PC), the parallel port interface completes the list. In the latter case, either a connection to a standard LPT port or to a separate board can be provided.
Software Features can significantly improve General characteristics scanner and reduce its advantages to advertising phrases. For example, a “competent” automatic converter of masked negatives allows you to obtain a positive image with reliable color reproduction on a good scanner, even without “finishing” adjustments. The opposite option is possible (although rare) - the disgusting conversion function will make the model practically useless for scanning negatives, requiring a huge amount of time to adjust the colors of the resulting image in the editor. A user-friendly interface of utilities significantly reduces scanning time (an ill-thought-out interface increases it many times). The software package with scanners usually comes with the so-called. TWAIN-driver - a special driver that allows you to access and control the scanner from various programs TWAIN-compatible graphics processing (for example, Adobe Photoshop). However, you should not confuse a TWAIN driver with a driver for the operating system - they have completely different purposes.
Completeness - equipping the scanner with the necessary devices and devices, cables, software, etc. An important characteristic in terms of readiness for work right out of the box (everything is there for connection, calibration, operation installed on a PC operating system, uploading slides and negatives). Completeness determines and additional features models when scanning in non-standard situations (for example, the presence of a special frame allows you to scan slides removed from thick frames, etc.).
It is clear that in addition to all the listed characteristics and aspects of slide scanners, the buyer is usually concerned about the cost of the model. The price range of options on the market that can be classified as amateur is extremely wide - from $125 to $2800 (in the case of the upper limit, it would be more correct to talk about the semi-professional category), while a higher price does not necessarily correspond to more attractive characteristics.
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 always write the shooting date in EXIF, and non-budget models 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
Buying 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, for which 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 terms of 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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