You may have heard expressions like "8-bit" And "16-bit". When people mention bits, they are talking about how many colors are in an image file. Photoshop color modes determine the bit depth of the image (1, 8, 16 or 32 bits). Since you will be working with these characteristics quite often (for example, when in the dialog box New you also have to choose the number of bits), it is useful to know what these numbers mean.

Bit— the smallest unit of measurement used by computers to store information. Each pixel in an image has bit depth, which controls how much color information a given pixel can contain.

So bit depth image specifies how much color information a given image contains. The higher the bit depth, the more colors can be displayed in an image.

Let's take a brief look at options with different numbers of bits in Photoshop.

1. In color mode, pixels can only be black or white. Images in this mode are called 1-bit, because each pixel can only be one color - black or white.

2. 8-bit image can contain two values ​​in each bit, which equals 256 possible color values. Why 256? Since each of the eight bits can contain two possible values, you get 256 combinations.

With 256 combinations for each channel in an RGB image, you can have over 16 million colors.

3. 16-bit images contain 65536 colors in one channel. They look the same as other images on the screen, but take up twice the space on your hard drive. Photographers really like these images because additional colors provide them with greater flexibility when adjusting parameters Curves And Levels, even though larger file sizes can greatly slow down the program.

Also, not all tools and filters work with 16-bit images, but the list of tools that work with them is growing every day. new version programs.

4. 32-bit images, which are classified as images with extended dynamic range(High Dynamic Range, HDR) contain more colors than you can imagine. But this will be discussed in future articles about HDR.

You'll mostly be dealing with 8-bit images, but if you have a camera that takes pictures at a higher bit depth, by all means, take a day off and experiment to see if the difference in quality is worth sacrificing some space on. hard drive and editing speed.

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One of the most important parameters of a digital image in photo processing is Color Depth, or color bit depth. You may have already come across this parameter, but not everyone gives it the importance it deserves. Let's figure out what it is, why it is needed and how to live with it.

Theory

Let's start, as always, with a short theoretical introduction, because a good theory gives an understanding of the processes occurring in practice. And understanding is the key to a high-quality and controlled result.

So, we are dealing with a computer, and in computers, as you know, all paths lead to binary code, or zeros and ones. But how many zeros and ones we can use to determine the color is what the color bitness tells us. For greater clarity, let's look at an example.

Below you can see a one-bit image. The colors in it are determined by only one digit, which can take the value 0 or 1, which means black and white, respectively.

Color depth - 1 bit

Now we move up a step to 2-bit images. Here the color is determined by 2 numbers at once, and here are all their possible combinations: 00, 01, 10, 11. This means that with a 2-bit color we already have as many as 4 possible colors.

Color depth - 2 bits

Similarly, the number of possible colors increases with each step, and in an 8-bit image it is already 256 colors. At first glance, it seems normal, especially since 256 colors are only for one channel, and we have 3 of them. As a result, this gives 16.7 million colors. But then you will see that this is not enough for serious processing.

16-bit color (and in fact in Photoshop it’s 15 bits + 1 color) gives us 32,769 colors per channel or 35 trillion colors in total. Do you feel the difference? This is completely invisible to the human eye... Until we throw a bunch of filters on our image.

What will happen?

Let's take a black and white gradient as a starting example.
To quickly and easily simulate the result of heavy processing, add 2 Levels layers with the following parameters:

Layers Levels

And this is the result we get for different color depths of the original image:

Gradient after applying filters

As you can see, the top 8-bit gradient has become clearly striped, while the 16-bit one retains a smooth transition (if you don't have a very high-quality monitor, you may see some striping on the bottom gradient as well). This effect of losing smooth color transitions is called posterization.

In real photographs, posterization can also appear on various gradients, in particular in the sky. Here is an example of posterization on a real image; for better visibility, the area where the effect is most noticeable has been cut out.

Posterization in photography

What to do?

Always ensure that your source images for processing are 16-bit. But keep in mind that converting an image from 8 bits to 16 will not give any useful effect, since there is initially no additional color information in such an image.
How to configure the conversion of a photo from RAW format to a 16-bit image in Adobe applications Camera Raw, Adobe Photoshop Watch Lightroom and DxO Optics Pro in the video below.

Today, technologies and devices make it possible to create such a bright and rich image that it will be even more beautiful than its real prototype. The quality of the transmitted image depends on several indicators: the number of megapixels, image resolution, its format, and so on. These include another property - color depth. What is it, and how to define and calculate it?

General information

Color depth is maximum number shades of color that the image can contain. This quantity is measured in bits (the number of binary bits that define the color of each pixel and hue in the image). For example, one pixel, the color depth of which is 1 bit, can take on two values: white and black. And the more important the color depth is, the more diverse the image will be, including many colors and shades. She is also responsible for the accuracy of image transmission. Here everything is the same: the higher, the better. Another example: drawing GIF format with a color depth of 8 bits will contain 256 colors, while an image JPEG format with a depth of 24 bits will include 16 million colors.

A little about RGB and CMYK

As a rule, all images in these formats have a color depth of 8 bits per channel (color). But the image may contain several color channels. Then the RGB image with three channels will have a depth of 24 bits (3x8). The color depth of CMYK images can reach 32 bits (4x8).

A few more bits

Color depth is the number of shades of the same color that a device in contact with images is capable of reproducing or creating. This parameter is responsible for the smooth transition of shades in images. All digital images are encoded using ones and zeros. Zero - one - white. They are stored and contained in memory, measured in bytes. One byte contains 8 bits, which indicate the color depth. For cameras, there is another definition - the color depth of the matrix. This is an indicator that determines how complete and deep images in terms of shades and colors a camera, or rather its matrix, can produce. Thanks to a high value of this parameter, photographs are voluminous and smooth.

Permission

The link between color depth and image quality is its resolution. For example, a 32-bit image with a resolution of 800x600 will be significantly worse than a similar one with 1440x900. Indeed, in the second case, a much larger number of pixels are involved. It's quite easy to verify this yourself. All you need to do is go to the “image settings” on your PC and try to successively reduce or enlarge. During this process, you will clearly see how much the resolution affects the quality of the transmitted image. Regardless of how many colors a given image contains, it will be limited to the maximum color that the monitor can support. As an example, you can take a monitor with a color depth of 16 bits and an image with 32 bits. This image on such a monitor will be displayed with a color depth of 16 bits.

Color depth

Color depth(color quality, image bit depth) - a computer graphics term meaning the amount of memory in the number of bits used to store and represent color when encoding one pixel raster graphics or video images. Often expressed as a unit bits per pixel (eng. bpp - bits per pixel) .

• 8-bit image. With a large number of bits in the color representation, the number of colors displayed is too large for color palettes. Therefore, with a large color depth, the brightness of the red, green and blue components is encoded - this encoding is the RGB model.
• 8-bit color V computer graphics– storage method graphic information V random access memory or in an image file, when each pixel is encoded as one byte (8 bits). The maximum number of colors that can be displayed simultaneously is 256 (28).

8-bit color formats

Indexed color. IN indexed (palette ) mode, any 256 colors are selected from a wide color space. Their meanings R, G And IN are stored in a special table - a palette. Each pixel of the image stores a color sample in the palette - from 0 to 255. 8-bit graphic formats Effectively compress images with up to 256 different colors. Reducing the number of colors is one of the lossy compression methods.

The advantage of indexed colors is high quality images - wide color gamut combined with low memory consumption.

Black and white palette. 8-bit black and white image - from black (0) to white (255) - 256 shades of gray.

Homogeneous palettes. Another format for representing 8-bit colors is the description of the red, green and blue components with low bit depth. This form of color representation in computer graphics is usually called 8-bit. TrueColor or a uniform palette (eng. uniform palette) .

12-bit color color is encoded in 4 bits (16 possible values) for each R-, G- and B -components, which allows you to imagine 4096 (16 x 16 x 16) different colors. This color depth is sometimes used in simple devices with color displays (for example, in mobile phones).

HighColor, or HiColor, designed to represent the full range of shades perceived by the human eye. This color is encoded with 15 or 16 bits, namely: a 15-bit color uses 5 bits to represent the red component, 5 for the green component and 5 for the blue component, i.e. There are 25 – 32 possible values ​​for each color, which gives 32,768 (32 × 32 × 32) colors combined. 16-bit color uses 5 bits to represent the red component, 5 bits for the blue component, and (since the human eye is more sensitive to green tones) 6 bits to represent the green component—therefore, there are 64 possible values. A total of 65,536 (32 × 64 × 32) colors.

LCD Displays . Most modern LCD displays display 18-bit color (64 x 64 x 64 = 262,144 combinations). Difference with truecolor- displays are compensated by flickering of pixel colors between their nearest 6-bit colors and (or) imperceptible to the eye dithering (English) dithering ), in which missing colors are made up from existing ones by mixing them.

Truecolor 24-bit image. Truecolor provides 16.7 million different colors. This color is closest to human perception and is convenient for image processing. 24-bit truecolor -color uses 8 bits each to represent the red, blue and green components, 256 different color representations for each channel, or a total of 16,777,216 colors (256 × 256 × 256).

32-bit color is an incorrect description of color depth. 32-bit color is 24-bit ( Truecolor ) with an additional 8-bit channel that determines the transparency of the image for each pixel.

Svsrkh-Truecolor. At the end of the 1990s. some graphics systems high-end began to use more than 8 bits per channel, such as 12 or 16 bits.

IN raster images to represent them, a rectangular grid of image elements (pixels) is used. Each pixel has a specific location and color value. When working with raster images, you edit pixels, not objects or shapes. Raster images are the most common way to convey non-rasterized images such as photographs or digital drawings because they convey subtle gradations of color and tone most effectively.

Raster images are resolution-dependent, meaning they contain a fixed number of pixels. When the screen is magnified too much or when printing at a lower resolution than the original resolution, details are lost and edges become jagged.

Example of a raster image with different magnification levels

Bitmap images sometimes require a lot of disk space to store, so they often require compression to reduce file size when used in some Creative Suite components. For example, before an image is imported into a layout, it is compressed in the application where it was created.

Note.

IN Adobe Illustrator You can create graphical raster effects for your drawings using effects and graphic styles.

About vector images

Vector images (sometimes called vector shapes or vector objects) consist of lines and curves given vectors- mathematical objects that describe an image in accordance with its geometric characteristics.

Vector images can be freely moved and resized without losing detail or clarity because they are resolution-independent. Their edges remain crisp when resized, printed on a PostScript printer, saved as a PDF file, or imported into a software application. vector graphics. Thus, vector images are best choice for illustrations that are displayed on various media and which have to be resized frequently, such as logos.

As an example vector images Examples include objects that are created in Adobe Creative Suite using the drawing tools and shape tools. Using copy and paste commands, you can use the same vector objects in different Creative Suite components.

Combination of vector and raster images

When using a combination of vector and raster images in one document, be aware that the image does not always look the same on the screen and on the final media (printed in a print shop, on a printer, or published on a web page). The quality of the final image is influenced by the following factors:

Transparency

Numerous effects are implemented in images using partially transparent pixels. If your image contains transparent areas, Photoshop performs a process called mixing. In most cases, the default mixing process works great. But if the image contains complex intersecting areas and must be output at high resolution, then a test review of the convergence results may be necessary.

Image Resolution

Number of pixels per inch (ppi) in raster image. Using too low a resolution when preparing an image for printing results in draft- images with large, spot-like pixels. Using too high resolution(when the pixel size is smaller than the minimum dot size that can be reproduced by the output device) increases the file size without improving the quality of the final image and slows down the printing process.

Printer resolution and raster lineature

The number of dots per inch (dpi) and the number of lines per inch (lpi) in a halftone screen. The relationship between image resolution, printer resolution, and screen lineature determines the quality of detail in the printed image.

Color channels

Each Photoshop image contains one or more channels, each of which stores information about the color elements of the image. The number of default color channels used in an image depends on the color mode. By default, bitmap, grayscale, duotone, and indexed color images contain one channel, RGB and Lab images contain three channels, and CMYK images contain four channels. Channels can be added to all types of images, except bitmaps. additional information see Color Modes.

Color image channels are actually grayscale images, each representing a different color component of the image. For example, an RGB image contains separate channels for red, green, and blue.

In addition to color channels, you can include in the image alpha channels, which are used as masks for saving and editing selections, and spot ink channels, which are used to add spot colors when printing. For getting additional information see Channel basics.

Bit depth

Bit depth determines the amount of color information available for each pixel in an image. The more bits of color information allocated to each pixel, the greater the number of colors available and the more accurate their display. For example, an image with a bit depth of 1 contains pixels with two possible color values: black and white. An 8 bit depth image can contain 2 8 or 256 different color values. Grayscale images with a bit depth of 8 can contain 256 different gray values.

RGB images are composed of three color channels. An RGB image with a bit depth of 8 can contain 256 different values ​​for each channel, meaning that a total of more than 16 million color values ​​can be represented. RGB images with 8-bit channels are sometimes called 24-bit images (8 bits x 3 channels = 24 bits of data per pixel).