Where are the channels in Photoshop? Selecting complex objects using Channels and Calculations. Simulating CMYK channels

Next to the layers panel there is another one - the Channels. Its purpose is to graphically display color information. Each channel is a separate component of the image.

So, what exactly is the point of this panel?

First, color channels contain information separated by color. For example, in mode RGB The image is divided into 3 channels: red , green , blue , and for CMYK– these are 4 channels: cyan , magenta , yellow , black . Thus, we can highlight the fact that Photoshop does not distinguish the color itself, but finds it by filtering, through overlaying channels on top of each other.

Secondly, there are also alpha channels. Like color channels, they support 256, 65536, 4,294,967,296 shades of gray. But unlike color channels, they do not contain information and represent opacity levels, masks. They can also be used to select an area and then save it (information about alpha channels is entered into the program, so memory is consumed, resulting in an increase in the size of the source file).

Let's take a closer look at using channels in Photoshop using the following example.


Go to the Channels panel – Window-Channels. We see a panel like Layers, only channels act as layers depending on the choice of display mode. We will use the mode RGB.

Here you can see 3 separate channels and 1 common:

RGB is a combined channel consisting of:

Red- red, Green- green, Blue- blue color.

If we make a selection of the car and save it, we will have a 4th channel: the alpha channel. As you already remember, this is a simple selection.



Now let's see what the channels for individual colors look like and find out how to use them. So, the red, green and blue channels in decreasing order are presented below.

You may notice that the white in the channel is relative to the red when viewed in RGB mode. Those. if you take it with a tool Eyedropper Tool color from the hood of the car, then going into the panel Window-Color we will see that the red color has a value of 255. Since our color is not red, but pink, the values ​​of green and blue in the panel Color will change.






It remains to look at the right panel menu Channels the points.

For work we will use the image of an apple.

Step 2

Let's start with the basics. Can you access the Channels palette through the Window menu? Channels. It is in the Channels palette that we will do most of the work.

Step 3

In the Channels palette we see four channels: RGB, Red, Green and Blue and they look the same as layers. But although channels look the same as layers, their functions are completely different. You may also notice that the channels reflect the current color mode of the document - in our case, the RGB color mode. Also, the Channels palette will change depending on the color mode of the document. This happens because each color mode uses a different method for determining color.

Step 4

I think many of you are familiar with the basic concepts of how colors mix, but that's just one aspect of how channels work. Let's look at the two main color structures. First, our file is in the RGB color mode, which is the color mode of computer monitors, televisions, and various portable devices. The RGB color model uses the concept of additive color, which combines red, green, and blue to create a full, rich color gamut.

Also, there is another color model - CMYK, which is intended for printing. Each of these two color models contains a set of color information - this information is reflected in the channels. Let's look at this in more detail. First, you need to open the image, and also open the Channels palette. If the image you have open is in RGB color mode, then you will see four different channels in the Channels palette. In fact, in this color mode there are three channels: red, green and blue, and the fourth channel is a channel that is created automatically by the program and does not carry color information. Each of the three channels displays three different streams of color that make up the image you open.

Step 5

By default, in Photoshop, in the Channels palette, all channels are presented in gray. Let's see how this can be changed. We will change the color of the channel with the red channel (Red).

Step 6

In the RGB channel, any white pixel will be at maximum brightness. At this point, the red channel will emit the maximum amount of red light. Conversely, where black shades are present, the pixel will not emit light for that color. So, just like the apple is red, the pixels that make up this part of the image are actually lighter. Conversely, if we convert the apple image to CMYK color mode, we will see something completely different. Now we have five channels: cyan, magenta, yellow, black, and also a channel that automatically combines all four channels.

In this case, the channels work differently, the way we work in a color space designed to simulate paint on paper. so you will see that where the pixel is white, that is the area of ​​the paper where nothing will be printed. Well, where the pixel is black, this will be the area where the paper is covered with this color as richly as possible.

As an example, let's look at the magenta channel. To create red, you can combine magenta with yellow. So if we were to print an image of an apple, a lot of magenta ink would be used. This is reflected in the purple channel.

Notice that areas of deep red are saturated with black tint, while some areas that contain a small amount of red tint are much whiter (reflection at the top of the apple). It turns out that channels are simply a way of dividing up different color information in a document, allowing you to customize and adjust color.

Personally, I prefer to work with grayscale in the channels. But if this is very difficult for you, there is another way in Photoshop to make it easier: go to the Edit menu? Preferences? Interface. In the dialog box that opens, check the box next to Show channels in color. After this, opening the Channels palette, you will see that the channel icons are colored in the corresponding colors: the red channel icon becomes red, the blue channel icon becomes blue, etc.

In CMYK color mode, the magenta channel will look like this:

I'll turn off the Show channels in color feature for now.

Step 7

RGB and CMYK color models are the most common color models. In addition to them, there are several more color models.

This color model is significantly different from the RGB and CMYK color models. This color model is not intended for mixing color, ink or light. In fact, it is designed to emulate human color perception. There are three main channels in the Lab color model. First is the Lightness channel, which controls the relative brightness and darkness of a particular pixel. The other two channels (called a and b) contain actual color information. This color model is used primarily for post-processing photographs and can be useful in establishing the correct color.

Multichannel images contain 256 gray levels for each channel and can be useful for specialized printing. The following information may be helpful when converting images to multichannel. Layers are not supported here, so they are flattened. The color channels of the original image become the spot color channels. Converting a CMYK image to multichannel mode creates cyan, magenta, yellow, and black spot color channels. Removing a channel from an RGB, CMYK, or Lab image automatically converts the image to multichannel by flattening the layers.

This color mode produces 8-bit images containing a maximum of 256 colors. When converted to indexed color mode, Photoshop builds an image color table (CLUT) that 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. This color mode allows you to reduce the file size of the image, while maintaining the image quality that is so necessary for multimedia presentations and web pages.

This mode uses different shades of gray. Each pixel in a grayscale image contains a brightness value ranging from 0 (black) to 255 (white). This color mode can be useful if you intend to print in non-color, or can be useful when separating objects from the background.

This color mode is the most basic of all existing color modes and consists entirely of black or white pixels. There aren't even shades of gray in it. This color mode uses only black and white channels and is not suitable for extracting objects from the background.

This is a completely different approach to working with color and this color mode is used primarily to add interesting color tones to a black and white photo (such as a sepia effect). Since this color mode only has one grayscale channel, it is also not suitable for separating objects from the background.

Command-Clicking Channels:

That's actually all I wanted to tell you about channels in this part of the lesson. By the way, if you need to create a selection from a channel, do Ctrl+Click on the thumbnail of the channel whose selection you need to get. The selection will be created based on the black, white and gray pixels of this channel. Well, read about other ways to work with channels in the second part of this lesson.

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Translated from the site www.myinkblog.com, the author of the translation is indicated at the beginning of the lesson.

Color information in Photoshop is stored in so-called channels. A channel is an image in which the points for each component color of a color model determine the brightness (amount) of that color. This is not easy to understand right away. Let's try to explain it more clearly.

Depending on the color model, an image may have three color channels (for RGB) or four (for CMYK). Each color of the model is allocated a separate channel, each channel contains a gray copy of the image. In channels, the gray level can have 256 gradations. The brightness of the gray point indicates the amount of color corresponding to the channel in the composite image. The lighter the point, the more color of that channel is used in the resulting point.

1. Upload any color image. If the image you uploaded was created in the CMYK color model, convert it to RGB.

2. Open the palette Channels. You see four points: RGB, Red, Green And Blue. Red, Green And Blue- these are the channels of your image.

3. Uncheck the eye-shaped channels for channels RGB, Red And Green. You will only have the channel on Blue(Fig. 7.1).

Rice. 7.1. Blue channel displayed

MULTIMEDIA COURSE

The “Color Channels” chapter on the CD included with the book contains several video lectures on working with color channels.

Notice that the image in the document window has turned gray. Moreover, it bears little resemblance to an ordinary black and white image. Some areas that seem to be light are dark, and vice versa. The thing is that grayscale shows how much blue color is involved in the formation of each color point. The lighter the dot, the more blue it contains. If there are completely black dots, it means that in the resulting color of these dots there is no blue at all or it is negligible. Look the same way Red And Green channels. You will see that the brightness of certain parts of the image does not correspond to reality. Let us emphasize once again that in this case the brightness of a point is determined not by the brightness of the resulting point, but by the brightness of the color of a given channel at this point.

Let's do a simple experiment.

1. Create a new image with a white background.

2. Select a tool Pencil. Adjust the brush so that the pencil line is thick enough, for example 50 pixels.

3. Choose a pure red color. To do this, in the color selection dialog box, specify the value R equal 255 , and the values G And B equal 0 . This is a color that consists only of red subpixels. Blue and green subpixels do not participate at all in this color (their brightness value is zero).

4. Draw a line in the window of the created document.

5. Open the palette Channels, then watch each channel separately.

Now let's describe what you should see.

Channel Red. You see a completely white image without any lines. The white background of the image indicates that white contains the maximum level of red (255). You also don’t see the line, since you drew it with a color in which the amount of red is also 255, that is, in this channel the intensity of the red subpixels is maximum over the entire area of ​​the drawing.

Channels Green And Blue. The backgrounds of these channels are white, since the participation of blue and green colors in white is also maximum (recall that white color is obtained when the value of all three RGB components is equal to 255). The line you drew in these channels is black. When you selected the tool color, you specified zero values ​​for the colors G And B, that is, the blue and green colors do not participate at all in the color you choose. This is why the line in these channels is black; this indicates that the level of the corresponding colors in these channels is minimal.

Now display simultaneously Red And Green channels. The background of the image turned yellow and the dot turned red. This is the result of mixing channels, that is, now we have superimposed Red channel on Green and at the same time excluded Blue channel. As a result, we added 255 gradations of red with the same amount of green and thereby obtained a yellow background. The line remained red because by 255 gradations of red in the channel Red added 0 gradations of red from the channel Green, that is, nothing was added.

If you add up the channels Green And Blue, excluding the channel Red, we get a turquoise background (the result of adding 255 gradations of green and blue) and a black line. Neither blue nor green colors are present in the line we drew (the level of these colors in the corresponding channels is zero), so the line remains black.

We will see a similar picture if we create an image in the CMYK color model. Only the CMYK channels, unlike RGB, are inverse, that is, the black and white colors in these channels are swapped. White color means the complete absence of dye, and black means the maximum amount of dye (100). For example, if we create an image with a white background and a magenta line (C = 0, M = 100, Y = 0 and K = 0), we will see the following in the channels.

Channels Blue, Yellow And Black will be completely white. These colors do not participate in the formation of a white background (the paper is already white in itself).

Channel Purple will contain a black line on a white background. This color also does not participate in the formation of the background, but in the line color the intensity of the purple color is maximum.

If we apply a line of a different color, for example green, on a white background, then in CMYK channels this line will be gray with different brightness. Green color is not present in the CMYK model, so it is obtained by mixing primary colors. The degree of brightness in each channel will depend on the amount of the corresponding color in the resulting green. The more of a certain color participates in the formation of the resulting color, the darker the line in the corresponding channel will be. To a greater extent, blue and yellow are involved in green. The proportion of magenta and black colors is not very high, so the lines on these channels will be very pale. Of course, it still depends on the shade of green. It is possible to create a color that has zero proportions of black and magenta, and it will be pure green.

We've talked about channels for so long, but we still haven't explained why they are needed. You may not use them at the initial stages and look at the palette at all Channels. Many people have been working with Photoshop for years and are completely unaware of the purpose for which channels are used, if not even aware of their existence. We agree that for an amateur this is not so important. However, when you grow to use Photoshop professionally, and especially if you work in organizations that produce printing products, you will certainly come across the concept of color separation. This is where you need channels.

Using channels it is very convenient to adjust the color scheme of an image. For example, when working with an RGB photograph, you notice that in a certain area the red color predominates. This is not easy to correct using conventional methods (levels) or other color correction. Yes, and it’s not always convenient. Turn off all channels except red, and, for example, the tool Dimmer you shade a given area of ​​the image, that is, you shade only the red color, thereby reducing the level of red in the composite color. You don’t even have to turn off other channels at the same time: just select a channel Red. However, with disabled channels it is easier to control your work.

Another use for channels is color separation. To print a picture on printing equipment, four gray images are required. These are exactly the channels we were talking about: CMYK channels. Typically, one image is printed on four transparencies and the contents of one channel are applied to each film. Next, based on the intensity (level) of black on each of the films, the equipment applies the appropriate amount of dye to the media, most often paper (Fig. 7.2).

Rice. 7.2. This is what the image looks like in individual CMYK channels.

It is not by chance that we use the term “media”, since the image can be printed on fabric, plastic and various polymer materials.

You can add a new channel to the image. However, this will not be a color channel, but a so-called alpha channel, or a mask channel. What can such channels be used for? There are many applications. The simplest thing is to use masks for images or high-quality retouching of graphics.

Try creating a new channel by clicking the third button from the left at the bottom of the palette Channels. Most likely, your entire image will appear to be covered with a translucent color film, and a new channel will appear in the channel list Alpha 1.

1. Now, having previously selected the channel Alpha 1, try to take the tool Eraser and erase part of the image. In the place where I “walked” Eraser, the image with the original colors will appear. In other words, you have created a semi-transparent alpha channel and made certain parts of it transparent (Figure 7.3).

Rice. 7.3. Part of the mask channel has been erased with an eraser.

2. Press the keyboard shortcut Ctrl+A, the entire image will be selected, and press the key Delete. The alpha channel content will be removed and the image will appear in its original colors.

3. Deselect by pressing the keyboard shortcut Ctrl+D.

4. Select a tool Brush and define a blue color for this tool.

5. Make sure the channel Alpha 1 is still highlighted.

6. Make a few strokes with the brush.

Please note that strokes appear in the image that are different from the color you selected, most likely red, that is, by “painting” with a blue brush, you can get red shades of strokes. This happens because the color of the brush is not actually blue, but a certain shade of gray. Take a look at the color swatch at the bottom of the toolbar to see for yourself. By adding gray lines to the alpha channel, you increase the brightness level of areas of the alpha channel's base color (red by default). As a result, the color of the channel is summed with the other channels.

Now a little about the alpha channel settings.

To call the alpha channel settings dialog box (Fig. 7.4), you need to double-click on the thumbnail of this channel in the palette Channels.

Rice. 7.4. Channel Options Dialog Box

The color swatch immediately catches your eye. The default is red. This is the alpha channel color. Remember that, no matter what brush color you choose, when you paint with the brush, red lines of varying brightness appear on the alpha channel (the brightness depends on the selected hue). You can change this color and then the lines drawn on the alpha channel will have a different color (of your choice).

In area Show in color by default the switch is set to position Masked areas. You've seen how the alpha channel works in this mode when drawing or erasing. If you select the position Selected areas, the alpha channel will act on the image in the opposite way, that is, the painted areas will become transparent, and the unpainted ones, on the contrary, will be opaque or translucent.

In field Opacity indicate the degree of opacity of the alpha channel. By default, the opacity level is 50 % , which is why you see the image clearly through “color film”.

It should be noted that you can create many alpha channels, adjust their opacity and color, and then apply any strokes or images in these channels. You can also copy the contents of any channel into an alpha channel, apply various corrections to it, etc. All this allows you to very finely tune the color parameters of the image, create original drawings, etc. If you really want, you can even turn black white image to color. To do this, you need to convert a black and white image to an RGB or CMYK model, create the required number of alpha channels (according to the number of colors in the model), copy the image into these channels and colorize individual fragments of the image so that when mixing the channels you get the desired colors. This, of course, is not easy and will require a lot of time, patience and experience, but it is possible! Indeed, you can turn an old black and white photograph into a color one. By the way, if all color channels contain absolutely the same information, it means that the proportions of all colors at individual points are equal. And the same proportions of colors are always a gray dot (in different gradations of brightness: from white to black). In other words, if the images in all color channels do not differ from each other, then the picture is black and white.

Understanding what you see in each channel gives you the knowledge to create complex highlights and fine-tune your images. In this article, you'll take a look inside the different color channels, starting with the most common image mode: RGB.

Let me make a reservation right away that the article does not cover. They are so important that they will be described in a separate article.

RGB channels

If you are preparing an image that will be sent to an inkjet printer, probably one you have at home (rather than a print shop), the mode RGB- what you need. After all, your monitor is RGB, just like your digital camera and scanner. Photoshop does not display individual channels in red, green and blue - they are shown in grayscale, so you can easily see the areas that are most saturated with color. Because colors in this mode are made of light, white indicates areas where the color is at its fullest, black indicates areas where it is faint, and shades of gray represent everything in between.

As you can see in the picture above, each channel contains different information:

Red. It is typically the lightest of the bunch and shows the most color variation. In the example given, it is very light, because there is a lot of red on the girl’s skin and hair. It can be very important when editing skin tone.

Green. You can think of it as the "contrast center" because it usually has the most contrast (this makes sense since digital cameras have twice as many green sensors as red or blue sensors). Keep this in mind when creating a layer mask to sharpen an image or when working with displacement maps.

Blue. Typically the darkest of the group, it can be useful when you need to create a complex selection to isolate an object. This is where you will encounter problems such as noise and grain.

CMYK channels

While you probably spend most of your time working with RGB images, you may also need to work with images in CMYK. Its name refers to cyan, magenta, yellow and black inks used by commercial printers to print newspapers, magazines, product packaging and so on. This mode also has a composite channel.

If you plan to print the image on a regular laser or inkjet printer, you won't need one. Plus, this mode robs you of several precious filters and adjustment layers. Professional letterpress printing, on the other hand, divides the CMYK of your image into individual color separations. Each division is a perfect copy of the color channel you see in Photoshop, printed in the appropriate color (cyan, magenta, yellow or black). When a printing press layers these four colors on top of each other, they form a full-color image (this technique is known as four-color printing).

Because they represent colors rather than light, grayscale information has the opposite meaning than RGB. In this mode, black indicates full strength and white indicates the weakest expression of the color.

Spot channels

In the CMYK printing environment, there is a special type of finished ink called spot color, which requires a special kind of channel. If you're a graphic designer working in pre-press, product design, or an advertising agency, you'll need to know how to work with spot colors.

Channels Lab

Lab mode Separates brightness values ​​(how bright or dark an image is) from color information. This color mode is not used for image output like the RGB and CMYK modes, but instead is useful when you want to change only the brightness values ​​of an image (while sharpening or brightening it), without shifting the colors.

In a similar way, you can adjust just the color information (say, to get rid of a hue) without changing the brightness value. And if you look at the palette, you will see images that look like x-rays.

The following channels are available in Lab mode:

• Brightness. It contains desaturated parts of the image, it looks like a really nice black and white version. Some people swear that by separating it into a new document and then doing a little editing, you can create a black-and-white image worthy of Ansel Adams.
• A. It contains half of the color information: a mixture of magenta (understand as "red") and green.
• b. the other half: a mixture of yellow and blue.

Multichannel mode

You will not need this mode unless you are preparing images for printing in a printing house. However, you may end up in this mode by accident. If you delete one of the document's color channels in RGB, CMYK, or Lab mode, Photoshop will switch the document to that mode without warning. If this happens, use the History palette to go back a step or press Ctrl+Z to undo your action.

There is no composite channel in this mode. This mode is designed exclusively for two- or three-color print jobs, so when you switch to it, the program will convert any existing color channels to spot ones.

When you convert an image to this mode, Photoshop immediately performs one of the following operations (depending on where you were previously):

• Converts RGB to cyan, magenta and yellow spot channels;
• converts CMYK to cyan, magenta, yellow and black spot;
• converts Lab into alpha channels named Alpha 1, Alpha 2 and Alpha 3;
• Converts Grayscale to spot black.

These changes cause drastic color shifts, but you can edit them individually, both the content and the spot color, to create the image you want.

Once you're done editing, save the image as a PSD or as a DCS 2.0 file if you need to transfer it to your prepress software.

Single channel modes

The other picture modes are not very interesting since they only have one channel. These modes include Bitmap, Grayscale, Duotone, and Indexed Color.

If you notice an error in the text, select it and press Ctrl + Enter. Thank you!

First, let's figure out what color channels are in Photoshop and what they are needed for.
Every Photoshop image contains one or more of these channels, each of which stores information about the color elements of the image.
In the most common document color model - RGB - the image consists of three channels - red, green and blue; this model gets its name from the first letters of the color names. For example, in the model for CMYK there are four channels, respectively, cyan, magenta, yellow and blak.
Each channel can contain 256 shades of color at 8-bit color resolution, 256 shades squared at 16-bit and 256 to the fourth power at 32-bit.

When a document is displayed on a monitor, the channels are mixed, resulting in a full color image. Moreover, they are mixed in a so-called additive manner, like rays of light, and the display result is brightened with the addition of each new channel.

You can view color channels in Photoshop in the appropriately named palette. You can open it by going to the main menu tab Window --> Channels. By default, the channel of each color is shown in the palette in shades of gray; in order for them to be displayed in the corresponding color, you should go to Edit --> Preferences --> Interface, where check the box "Show Channels in Color" item.

The palette in RGB mode shows four channels, not three, i.e. one more. (accordingly, in CMYK mode - five instead of four). This is because at the top of the palette the resulting channel is shown, showing the finished one, i.e. an image combined from three channels.

The practical applications of using color channels are endless.

I will give one example with which you can understand the usefulness of using this tool: red-eye removal using channels.

A practical example of using channels in Photoshop

Open a photo that has an unwanted red-eye effect.
Select the red pupils with the selection tool.
Go to the channels palette, click on the blue one, press the key combination Ctrl+C, i.e. copy the contents of the selected area of ​​the blue channel
Click on the red channel, press Ctrl+C, i.e. paste the contents of blue into red.
Click on the green channel and repeat the steps with the blue one.
Click on the top RGB channel and look at the finished result, where the redness of the pupils has been eliminated. and the glare and gloss are preserved.