Familiarity with color channels (RGB, CMYK, Spot, Lab, multi-channel and single-channel modes). rgb color model

Various color modes:

RGB mode (millions of colors)
CMYK mode (four-color printing colors)
Indexed color mode (256 colors)
Grayscale mode (256 shades of gray)
Bit mode (2 colors)

A color mode, or picture mode, determines how colors are combined based on the number of channels in the color model. Different color modes give different levels color detail and file size. For example, use the CMYK color mode for images in a full-color printed brochure, and the RGB color mode for images intended for the web or email to reduce file size while maintaining true colors.

RGB color mode

RGB mode in Photoshop uses the RGB model, assigning an intensity value to each pixel. In 8-bit-per-channel images, intensity values range from 0 (black) to 255 (white) for each of the RGB color components (red, green, blue). For example, the color bright red has a value of R=246, G=20 and B=50. If the values of all three components are the same, the result is neutral-neutral darkening. gray. If the values of all components are equal to 255, then the result is pure white, and if 0, then pure black.

To reproduce colors on screen, RGB images use three colors, or channel. In 8-bit-per-channel images, each pixel contains 24 bits (3 x 8-bit channels) of color information. In 24-bit images, three channels produce up to 16.7 million colors per pixel. In 48-bit (16 bits per channel) and 96-bit (32 bits per channel) images, each pixel can produce even more colors. In addition to being the default mode for new images created in Photoshop, the RGB model is also used to display colors computer monitors. This means that when working in color modes non-RGB (such as CMYK), Photoshop converts the image to RGB for display on the screen.

Although RGB is the standard color model, the exact range of colors displayed may vary depending on the application and output device. Photoshop's RGB mode changes depending on the workspace settings you make in the dialog box "Adjusting Colors".

CMYK mode

In CMYK mode, the pixel for each process ink is assigned a percentage value. The lightest colors (highlight colors) are assigned a lower value, and the darker colors (shadow colors) are assigned a higher value. For example, a bright red color might be made up of 2% cyan, 93% magenta, 90% yellow and 0% black. In CMYK images, if all four components are 0%, the result is pure white.

The CMYK mode is designed to prepare an image for printing using process colors. The result of converting an RGB image to CMYK is color separation. If the original image was RGB, it is best to edit it in RGB mode and only convert it to CMYK at the very end of the edit. In RGB command mode "Proof Settings" allow you to simulate the effects of CMYK conversion without changing the data itself. CMYK mode also allows you to work directly with CMYK images taken from a scanner or imported from professional systems.

Although CMYK is the standard color model, the exact range of colors reproduced may vary depending on the press and printing conditions. Photoshop's CMYK mode changes depending on the workspace settings you make in the dialog box "Adjusting Colors".

Lab color mode

Color model L*a*b* (Lab) of the International Illuminating Commission is based on the perception of color by the human eye. In Lab mode, numerical values describe all the colors that a person with normal vision sees. Because Lab values describe what a color looks like, rather than how much of a particular ink a device (such as a monitor, desktop printer, or digital camera) for color reproduction, the Lab model is considered hardware independent color model. Color management systems use Lab as a color reference to produce predictable results when converting color from one color space to another.

In Lab mode there is a brightness component (L) that can range from 0 to 100. In the palette Adobe colors and in the Color panel components a(green-red axis) and b(blue-yellow axis) can have values ranging from +127 to –128.

Lab images can be saved to following formats: Photoshop, Photoshop EPS, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, TIFF, Photoshop DCS 1.0 and Photoshop DCS 2.0. 48-bit (16-bit per channel) Lab images can be saved in Photoshop, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, and TIFF formats.

Note.

DCS 1.0 and DCS 2.0 files are converted to CMYK upon opening.

Grayscale mode

Grayscale mode uses different shades of gray in images. 8-bit images allow up to 256 shades of gray. Each pixel in a grayscale image contains a brightness value ranging from 0 (black) to 255 (white). 16- and 32-bit images have significantly more shades of gray.

Grayscale values can also be expressed as a percentage of total black paint coverage (a value of 0% is equivalent to white and 100% is equivalent to black).

Grayscale mode uses the range determined by the workspace settings specified in the dialog box "Adjusting Colors".

Bit mode

Bit mode represents each pixel in an image as one of two values (black or white). Images in this mode are called bitmap (1-bit) images because there is exactly one bit per pixel.

Duplex mode

Duplex mode creates monotone, duplex (two-color), triotone (three-color), and tetratone (four-color) grayscale images using one to four custom inks.

Indexed Colors Mode

Indexed Colors mode produces 8-bit images with a maximum of 256 colors. When converted to indexed mode Photoshop flowers builds image color table (CLUT), which stores and indexes the colors used in the image. If the color of the source image is not in this table, the program selects the closest available color or performs dithering to simulate the missing color.

Although this mode has a limited color palette, it can reduce the file size of an image while maintaining the image quality needed for multimedia presentations, web pages, etc. Editing capabilities in this mode are limited. If you need to do a lot of editing, you should temporarily switch to RGB mode. In indexed color mode, files can be saved in the following formats: Photoshop, BMP, DICOM (medical format digital images and communications), GIF, Photoshop EPS, Large Document Format (PSB), PCX, Photoshop PDF, Photoshop Raw, Photoshop 2.0, PICT, PNG, Targa® and TIFF.

Multi-channel mode

Multichannel images contain 256 gray levels for each channel and can be useful for specialized printing. These images can be saved in the following formats: Photoshop, Large Document Format (PSB), Photoshop 2.0, Photoshop Raw, and Photoshop DCS 2.0.

The following information may be helpful when converting images to multichannel.

Layers are not supported and are therefore flattened.

The color channels of the original image become spot color channels.

Converting a CMYK image to multichannel mode creates cyan, magenta, yellow, and black spot color channels.

Converting an RGB image to multi-channel mode creates cyan, magenta, and yellow spot color channels.

Removing a channel from an RGB, CMYK, or Lab image automatically converts the image to multichannel by flattening the layers.

To export a multi-channel image, you need to save it in Photoshop format DCS 2.0.

Note.

Images with indexed and 32-bit colors cannot be converted to Multichannel mode.

The RGB model describes the colors emitted. It is based on three primary (basic) colors: red (Red), green (Green) and blue (Blue). The RGB model can be called “native” for the display. The remaining colors are obtained by combining the basic ones. This type of color is called additive.

From the figure it can be seen that the combination of green and red produces yellow, the combination of green and blue produces blue, and the combination of all three colors- white. From this we can conclude that colors in RGB are added subtractively.

Primary colors are taken from human biology. That is, these colors are based on the physiological reaction of the human eye to light. The human eye has photoreceptor cells that respond to most green (M), yellow-green (L) and blue-violet (S) light ( maximum length waves from 534 nm, 564 nm and 420 nm respectively). The human brain can easily distinguish a wide range of different colors based on differences in the signals received from the three waves.

Most widely RGB color the model is used in LCD or plasma displays such as a TV or computer monitor. Each pixel on a display can be represented by a hardware interface (e.g. graphic cards) as red, green and blue values. RGB values vary in intensity, which are used for clarity. Cameras and scanners also work in the same way, they capture color with sensors that record different RGB intensities at each pixel.

In 16 bits per pixel mode, also known as Highcolor, there are either 5 bits per color (often referred to as 555 mode) or with an extra bit for green (known as 565 mode). The color green is added due to the fact that the human eye has the ability to detect more shades of green than any other color.

RGB values, represented in 24 bits per pixel (bpp) mode, also known as Truecolor, typically have three integer values between 0 and 255. Each of these three numbers represents the intensity of red, green, and blue, respectively.

RGB has three channels: red, blue and green, i.e. RGB is a three-channel color model. Each channel can take values from 0 to 255 in decimal or, more realistically, from 0 to FF in hexadecimal. This is explained by the fact that the byte with which the channel is encoded, and indeed any byte, consists of eight bits, and a bit can take 2 values 0 or 1, for a total of 28=256. In RGB, for example, red can have 256 gradations: from pure red (FF) to black (00). Thus, it is easy to calculate that the RGB model contains only 2563 or 16777216 colors.

RGB has three channels, and each is encoded with 8 bits. The maximum value, FF (or 255), gives a pure color. White color is obtained by combining all colors, or rather, their extreme gradations. White color code = FF(red) + FF(green) + FF(blue). Accordingly, black code = 000000. Yellow code = FFFF00, magenta = FF00FF, cyan = 00FFFF.

There are also 32 and 48 bit color display modes.

RGB is not used for printing on paper; instead, there is a CMYK color space.

CMYK is a color model used in color printing. A color model is a mathematical model for describing colors using integers. The CMYK model is based on cyan, magenta, yellow and black.

Did you know that Photoshop is colorblind?
When I say colorblind, I don't mean that I have slight problems seeing shades of green and purple. I mean he's completely color blind. All Photoshop sees is black and white. Black, white and many shades of gray in between. The most powerful graphic editor in the world, the industry standard among photographers, designers and virtually all creative professionals, capable of producing millions and even billions of colors, has no idea what color is.

You may be looking at a photo of a crystal blue ocean you took on your last vacation, but Photoshop sees it as a gray ocean. Have you ever captured a rainbow crossing the sky after an evening summer storm? Photoshop sees it as a beautiful set of shades of gray. What about the famous pot of gold? For Photoshop it's just a big pot of something gray.
Don't sympathize with Photoshop. He is absolutely happy in his colorless world.

In fact, the only reason Photoshop shows us images in color is because people themselves expect to see them in color. We wouldn't know what to think if everything was shown in black and white. But not Photoshop. There is nothing more precious to him than black, white and gray colors.

So Photoshop has no idea what color is in front of it and all it knows and sees is black, white and gray, how does it show us images in color? I mean this image, which is open in Photoshop:

Photo open in a Photoshop document window.

Obviously, this boy (or girl) is colored. Well, really, I don't think there are more colorful birds than this one. But it's not just birds here. The leaves on the background are colored. The piece of wood on which the bird is sitting is also in color. Everything in the image is in color! And this image is open in Photoshop, so how can this be if Photoshop is color blind? And if he really doesn't see color, how does Photoshop do this? great job showing us something he can't see?

To answer this question we need to consider two things. First - color modes (colormode) and the second - color channels (channels). Both are very interconnected, if you understand color modes (colormode), That color channels (colorchannels) will also become clearer to you.

We know, or at least have accepted, the fact that Photoshop doesn't see color. All he sees is black, white and gray. So how does it take those blacks, whites and grays and turn them into the colors we see on our screen? The answer is addiction. Dependence on what, you ask? It's an addiction color mode (colormode), which uses Photoshop.

There are quite a few color modes in Photoshop, but the two main ones are RGB and CMYK. A couple of others you might have heard while working with Photoshop are: Grayscale(Grayscale) and Lab (pronounced “el-ey-bee,” but not “Lab”). These are all examples of color modes, and they define how Photoshop translates its black and white information into color, with the exception of color mode Grayscale(Grayscale), which does not use colors. It's strict black and white mode, and quite often it is used to quickly convert a color image to black and white.

Of all the four modes that I mentioned, the only one we will consider is RGB. The CMYK mode is suitable for printing and publications, we will return to it some other time. Mode Grayscale(Grayscale) as I said, it is used strictly for black and white images, and the Lab mode is not understood by most people living on this planet, as well as those living on other planets, although it is often used for professional editing images, but even the people who use it don't have a complete understanding of how it works. Which leaves us with only RGB.

By far the most widely used color mode in computers and technology in the world is the RGB color mode. Photoshop uses it, other programs on your computer use it, your monitor, digital camera and scanner, your TV, and even small screen your mobile or iPod is used this mode, as well as portable gaming systems like PSP Sony or Nintendo DS. If it is a device that somehow displays or creates images, or software For image editing, similar to Photoshop, it uses the RGB color mode. Sounds quite loud, doesn't it? And of course it is. For everything it has quite a wide meaning and importance, RGB is an abbreviation of three colors − red(red), green(green) and blue(blue).

RGBand color channels: the color world of red, green and blue.
What is so unusual about these three colors - red, green and blue? Yes, in general, only that they are primary colors. What does it mean? This means that every color you and I see is created from some combination of red, green and blue. How do we get yellow? By mixing red and green. How do we get purple? By mixing red and blue. What about orange? 100% red and 50% green. And that's just simple examples. Every single color we see is created by a combination of these three colors. I know it sounds almost unreal, but it's true.
When you mix the brightest versions of these colors together, you get pure white. When you completely remove all three of these colors, you get pure black. And when you mix equal amounts in percentages ranging from 0 to 100%, you get shades of gray.
Let's look at our bird image again:

A very colorful image indeed, but where do all these colors come from? To explain for beginners, let's look at the information that is told to us at the top of the Photoshop document window:

Information at the top of the document window.

What I've marked with the red circle is that Photoshop is telling us that the image is in the RGB color mode, which means that every color we see in the photo is created from some combination of red, green, and blue. If you want to verify this, all you need to do is hover your mouse over any part of the image and look at Information panel (Info) in Photoshop.
I'll hover my mouse over the tip of the beak near the bright red area.

Hover your mouse over the tip of the bird's beak.

Let's go to the panel Information(Info) in Photoshop to see what it tells us about this point in the image:

Photoshop Information Panel.

The part that interests us in the panel Information(Info) Photoshop, located at the top left, it shows us the RGB values. The only thing you need to understand is that Photoshop doesn't render RGB colors as a percentage, that is, we will not see values like “10% red(red), 40% green(green) and 50% blue(blue)". Instead, RGB has values from 0 to 255, where 0 means that the specified color is completely absent from the image, and 255 indicates that the full color is used.

So if we look at the area that I highlighted, we can see that the point contains the values 216 for red(red) (very great value), 59 green(green) (quite small value) and 1 blue(blue) (could be 0), which means that at this point there is practically no blue color, and a very small amount of green. The vast majority of the color comes from red, which is generally natural since the bird's beak is definitely red.
Let's look at another point. I hover my mouse over the area around the bird's back:

Hover the mouse cursor over a point in the bird's back area.

This area looks quite green to me, and if we look at what the panel tells us Information(Info):

Photoshop's Info panel, showing us the RGB values for an area of the image.

Then we will make sure that green(green) is the dominant color with a value of 180. Red(red) has a value of only 20, which is a very small value, and blue(blue) even less than 16.
Let's do this again. I'll hover my mouse cursor somewhere around the bird's head:

Hover the mouse cursor over a point near the bird's head.

This time blue should have more high value in the panel Information(Info):

Photoshop's Info panel showing RGB information for a point selected on the bird's head.

And again we were convinced that this time blue(blue) color has a predominant value of 208 and is the dominant color. Of course, the bird's head is not pure blue. It's more purple-blue, which explains why green(green) has a great value of 100, and even red(red) has a fairly large value of 90. All three colors mixed together on the screen to create the purple-blue color we see.

I could keep hovering over any point in the photo (I don't want to, but I could) and we could watch the values change red(red), green(green) and blue(blue) in the panel Information(Info), since each individual color in the image consists of a certain combination of these three colors.
This is how RGB mode works. Let's repeat, RGB means nothing more than Red (R ed), Green (G reen) and Blue (B lue), and because this image is in RGB mode, Photoshop represents each color using combinations of red, green, and blue.
The next thing we will look at in the second part of the image is - color channels(color channel).

On at the moment We found out that Photoshop doesn't see color. Everything in the world of Photoshop is created from black, white and some shades of gray. We also learned that Photoshop uses the RGB color mode to display colors on screen by mixing different combinations red(red), green(green) and blue(blue). But how does Photoshop know how much red, green, and blue to mix to make a single color on screen when it doesn't know what color it should be? I mean, it's great that Photoshop can render pure yellow by mixing full color red(red) with a value of 255, and also green(green) with the same value, but how does it know that yellow should be displayed?
The answer is no. How, no way?

And here it is. Photoshop doesn't know that you expect to see yellow in a certain part of the image. It only knows that it is displayed when red(red) with a value of 255 and green(green) with a value of 255, and excludes blue(blue). If this combination creates exactly the color you and I call “yellow,” then great, but Photoshop isn't left out. All he knows is to “display red(red) with a value of 255, green(green) – 255 and blue(blue) 0 at a specific pixel." When adding different colors to images, Photoshop is a paint-by-numbers artist.

So, since Photoshop adds a certain amount red(red), green(green) and blue(blue). How does he know how much of each color to add when all he understands is black, white and gray? Two words... Color channels(Color Channels).
Let's look at the bird image again:

So we see this image with you. This is how Photoshop sees it:

But, wait. He also sees it like this:

But how does he see it in two different black and white versions? Good question. The answer is no. He sees it in three different black and white versions. Here's a third one:

Everything we see in one color image, Photoshop sees in three separate ones. black and white images X. Each of these images represents a color channel. The first represents the red channel, the second represents the green, and the third represents the blue. Three separate channels for three different colors combined together will create a full color image.

Think of color channels as color filters. While Photoshop displays a color image on the screen, it knows which colors to display due to the brightness of the light passing through the filters. First it illuminates through a red filter (red channel). If no light passes through the filter, Photoshop knows to display red with a value of 0. If all light passes through the filter, then Photoshop displays full red with a value of 255. If the amount of light passing through the filters is slightly less, Photoshop displays red color with a value between 0 and 255, depending on how much light passes through the filter. It then does the same with the green filter (green channel), setting it to 0 if no light passes through the filter, 255 if all the light passes through the filter, and some value between 0 and 255 if some light passes through. Then he does the same with the blue filter (blue channel). It then knows what value to set red, green and blue to and combines them to create the color we see. It does all this for every pixel in your image, so if your image contains millions of pixels, like most photos taken with a digital camera these days, Photoshop does this operation a million times just to display the image you see. on the screen. See how much Photoshop loves you? So, a second ago I said that Photoshop is not left behind. Let's move on.
Photoshop's "filters" use those three separate black and white images we saw. Red:

So how does Photoshop use this black and white image as a red filter? Remember how I said that Photoshop assigns red values from 0-255 based on how much light passes through the filter? So, how much light passes through the filter depends on how bright the black and white portions of the image are. Any area of pure black will not allow any light to penetrate, this means that in these areas of the image the red value will be 0. Any areas of pure white that allow all light to penetrate, in these areas the red value will be equal to 255. And in areas with the various shades of gray, which are the majority in an image, some amount of light passes through depending on how light or dark the gray area is represented.

In the image above we can see that the brightest areas of the image are in the bird's beak and chest, which confirms what I just said: these areas contain more red in full color. Likewise, the areas of the back, wings and belly are very dark, so there should not be much or no red in these areas.
Let's look again at the full color version of the image:

We said that the beak and chest should contain a lot of red, and as you can see, it does! We also said that the back, wings and belly shouldn't have much or no red in them, and I really don't see any red on them.
Let's look again at the black and white image that Photoshop uses for the green channel:

This black and white image contains a lot of highlights, which means there should be a lot of green in the photo. What's also strange is that one of the brightest areas in the image is near the bird's chest, but I don't remember it being there green. Let's check this by looking at the full color image again:

There is, of course, a lot of green in the image, which explains the many bright shades of gray in the black and white image. If I look at the side of the bird's chest that had the brightest area in the black and white image, it won't be green. In fact it is very yellow! How is this possible? Just. Red and green combined make yellow, so to represent yellow, Photoshop mixed red and green together.
Let's look at another black and white image that Photoshop uses as its blue channel:

There are a lot of very dark areas in this image, especially on the bird itself, with the exception of the head, which is very light. This should mean that only one part of the bird will appear blue - its head. Although her belly should also have a noticeable amount of blue, so should her legs and the piece of wood she's sitting on. Let's see:

We were convinced that the bird's head was very blue, we also saw that its belly, as well as its legs and a piece of wood, were also blue. The rest of the bird does not have noticeable blue areas, which is why dark areas appeared in these places in the black and white image.
We've figured out everything about how the RGB color mode and color channels work in Photoshop, everything except one thing. We still haven't seen where you can access these color channels. You'll find them in the appropriately named panel Channels(Channels), which are grouped together with the palette layers(Layers).

Channels panel (Channels) Photoshop.

Palette Channels(Channels) looks about the same as the palette layers(Layers), only it shows information about color channels(color channels) instead of layers. Here you see one Red(Red), one Green(Green) and one Blue(Blue) channel, and each of them contains its own version of a black and white image, exactly like the one I showed in this tutorial. The topmost "RGB" channel is not really a channel. This is simply a combination of three channels, giving us a full-color photo. You can click individually on each channel in the palette Channels(Channels) to display its black and white image in the document window.
That's all. We now know that Photoshop sees everything through the lens of black, white and gray colors. We know that using RGB mode (set by default anyway) mixes different quantities red, green and blue to produce the full color image we see on our screens. And we also know that depending on how much red, green and blue, the black and white version of the image for each of the three channels will be different, so all these operations are performed for each individual pixel in the image. And thus, you and I can see a full-color version of the image, while Photoshop is content with black and white.
Now we know how much Photoshop loves us. This concludes this lesson.

Why are different color models needed and why the same color can look different

Providing design services both in the field of web and in the field of printing, we often come across a question from the Client: why do the same corporate colors in the design layout of the website and in the design layout of printed products look different? The answer to this question lies in the differences between color models: digital and printed.

Color computer screen varies from black (the absence of color) to white (the maximum brightness of all components of color: red, green and blue). On paper, on the contrary, the absence of color corresponds to white, and the mixing of the maximum number of colors corresponds to dark brown, which is perceived as black.

Therefore, when preparing for printing, the image must be converted from additive ("folding") flower models RGB into subtractive (“subtractive”) CMYK model. CMYK model uses the opposite colors of the original - the opposite of red is cyan, the opposite of green is purple and the opposite of blue is yellow.

Digital RGB color model

What is RGB?

The abbreviation RGB means the names of three colors used to display a color image on the screen: Red (red), Green (green), Blue (blue).

How is RGB color formed?

The color on the monitor screen is formed by combining rays of three primary colors - red, green and blue. If the intensity of each of them reaches 100%, then the color white is obtained. The absence of all three colors produces black.

Thus, any color that we see on the screen can be described by three numbers indicating the brightness of the red, green and blue color components in the digital range from 0 to 255. Graphics programs allow you to combine the desired RGB color from 256 shades of red, 256 shades of green and 256 shades of blue. The total is 256 x 256 x 256 = 16.7 million colors.

Where are RGB images used?

RGB images are used to display on a monitor screen. When creating colors for viewing in browsers, the same RGB color model is used as a basis.

Printing color model CMYK

What is CMYK?

The CMYK system is created and used for typographic printing. The abbreviation CMYK stands for the names of the primary inks used for four-color printing: cyan (Cyan), magenta (Magenta) and yellow (Yellow). The letter K stands for black ink (BlacK), which allows you to achieve a rich black color when printing. The last letter of the word is used, not the first, to avoid confusion between Black and Blue.

How is CMYK color formed?

Each of the numbers that define a color in CMYK represents the percentage of paint of that color that makes up the color combination. For example, to obtain a dark orange color, you would mix 30% cyan paint, 45% magenta paint, 80% yellow paint and 5% black paint. This can be expressed as follows: (30/45/80/5).

Where are CMYK images used?

The scope of application of the CMYK color model is full-color printing. It is this model that most printing devices work with. Due to color model mismatches, there is often a situation where the color you want to print cannot be reproduced using the CMYK model (for example, gold or silver).

In this case, Pantone inks are used (ready-made mixed inks of many colors and shades), they are also called spot inks (since these inks are not mixed during printing, but are opaque).

All files intended for printing must be converted to CMYK. This process is called color separation. RGB covers a larger color range than CMYK, and this must be taken into account when creating images that you later plan to print on a printer or printing house.

When viewing a CMYK image on a monitor screen, the same colors may appear slightly differently than when viewing an RGB image. It is impossible to display very bright colors RGB models, the RGB model, in turn, is not able to convey the dark, dense shades of the CMYK model, since the nature of the color is different.

The color display on your monitor screen changes frequently and depends on lighting conditions, monitor temperature, and the color of surrounding objects. In addition, many of the colors visible in real life, cannot be printed, not all colors displayed on the screen can be printed, and some printing colors are not visible on the monitor screen.

Thus, when preparing a company logo for publication on the website, we use the RGB model. When preparing the same logo for printing in a printing house (for example, on business cards or letterhead), we use a CMYK model, and the colors of this model on the screen may be visually slightly different from those we see in RGB. There is no need to be afraid of this: after all, on paper, the colors of the logo will closely match the colors that we see on the screen.

RGB mode

RGB mode in Photoshop uses the RGB model, assigning an intensity value to each pixel. In 8-bit-per-channel images, intensity values range from 0 (black) to 255 (white) for each of the RGB color components (red, green, blue). For example, the color bright red has a value of R=246, G=20 and B=50. If the values of all three components are the same, the result is a neutral gray shading. If the values of all components are equal to 255, then the result is pure white, and if 0, then pure black.

To reproduce colors on screen, RGB images use three colors, or channels. In 8-bit-per-channel images, each pixel contains 24 bits (3 x 8-bit channels) of color information. In 24-bit images, three channels produce up to 16.7 million colors per pixel. In 48-bit (16 bits per channel) and 96-bit (32 bits per channel) images, each pixel can produce even more colors. In addition to being the default mode for new images created in Photoshop, the RGB model is also used to display colors on computer monitors. This means that when working in color modes other than RGB (such as CMYK), Photoshop converts the image to RGB for display on the screen.

CMYK mode

The CMYK mode is designed to prepare an image for printing using process colors. Converting an RGB image to CMYK results in color separation. If the original image was RGB, it is best to edit it in RGB mode and only convert it to CMYK at the very end of the edit. In RGB mode, the Proof Settings commands let you simulate the effects of CMYK conversion without changing the data itself. CMYK mode also allows you to work directly with CMYK images taken from a scanner or imported from professional systems.

Lab mode

The International Illuminating Commission's L*a*b* (Lab) color model is based on the perception of color by the human eye. In Lab mode, numerical values describe all the colors that a person with normal vision sees. Because Lab values describe what a color looks like, rather than how much of a particular ink a device (such as a monitor, desktop printer, or digital camera) requires to reproduce colors, the Lab model is considered a device-independent color model. Color management systems use Lab as a color reference to produce predictable results when converting color from one color space to another.

Lab mode has a luminance (L) component that can range from 0 to 100. In the Adobe Color Picker and Color panel, the a (green-red axis) and b (blue-yellow axis) components can range from range from +127 to –128.

Lab images can be saved in the following formats: Photoshop, Photoshop EPS, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, TIFF, Photoshop DCS 1.0, and Photoshop DCS 2.0. 48-bit (16-bit per channel) Lab images can be saved in Photoshop, Large Document Format (PSB), Photoshop PDF, Photoshop Raw, and TIFF formats.

Note. DCS 1.0 and DCS 2.0 files are converted to CMYK upon opening.

Grayscale mode

Grayscale values can also be expressed as a percentage of total black paint coverage (a value of 0% is equivalent to white and 100% is equivalent to black).

Grayscale mode uses the range determined by the workspace settings specified in the Color Adjustment dialog box.

Bit mode

Bit mode represents each pixel in an image as one of two values (black or white). Images in this mode are called bitmap (1-bit) images because there is exactly one bit per pixel.

Duplex mode

Duplex mode creates monotone, duplex (two-color), triotone (three-color), and tetratone (four-color) grayscale images using one to four custom inks.

Indexed Colors Mode

Indexed Colors mode produces 8-bit images with a maximum of 256 colors. When converted to indexed color mode, Photoshop builds an image color table (CLUT), which stores and indexes the colors used in the image. If the color of the source image is not in this table, the program selects the closest available color or dithers to simulate the missing color.

Although this mode has a limited color palette, it can reduce the file size of an image while maintaining the image quality needed for multimedia presentations, web pages, etc. Editing capabilities in this mode are limited. If you need to do a lot of editing, you should temporarily switch to RGB mode. In Indexed Color mode, files can be saved in the following formats: Photoshop, BMP, DICOM (Digital Imaging and Communications Format), GIF, Photoshop EPS, Large Document Format (PSB), PCX, Photoshop PDF, Photoshop Raw, Photoshop 2.0, PICT, PNG, Targa® and TIFF.

Multi-channel mode

The following information may be helpful when converting images to multichannel.

Layers are not supported and are therefore flattened.

The color channels of the original image become the spot color channels.

Converting a CMYK image to multi-channel mode creates cyan, magenta, yellow, and black spot color channels.

Converting an RGB image to multi-channel mode creates cyan, magenta, and yellow channels of spot colors.

Removing a channel from an RGB, CMYK, or Lab image automatically converts the image to multichannel by flattening the layers.

To export a multi-channel image, you must save it in Photoshop DCS 2.0 format.

Note. Images with indexed and 32-bit colors cannot be converted to Multichannel mode.