Photoshop can remove all color channels. Color channels in Photoshop
In this tutorial, we'll learn how to enhance the contrast and brightness of images in creative ways by applying blend modes to individual color channels. If you are familiar with Photoshop, then of course you know that we usually select blending modes in the layers panel when we want to change the interaction or combination of a layer with the underlying layer/layers.
I'll show you how to apply blend modes not to an entire layer, but to the individual RGB color channels (red, green, and blue channels) that Photoshop uses to create a full color image.
How do we apply blend modes to color channels? In fact, doing this is simple and easy thanks to the External Channel (Apply Image) command.
Working with color channels in Photoshop is a bit of a difficult topic for a novice user. I will touch on it superficially in this lesson, but for those who are just starting to work with channels in Photoshop, I strongly recommend that you first read the lesson "ModelRGB and color channels". After reading the material, you will better understand what will happen when further work With dialog box"External channel" in this lesson.
To learn more about blending modes, I recommend that you read the tutorial about blending modes, which explains how the basic blending modes work in Photoshop.
In this tutorial I will be working in Photoshop CS6, but later versions will also work. Here's the photo I currently have open in the program:
Original image
The first thing we need to do before moving on to further work with the image is to create a copy of it. If we look at the Layers panel, we'll notice that the original image is placed on the Background layer:
The Layers panel shows that the image is placed on the Background layer
Let's quickly make a copy of the background layer by pressing the keyboard shortcut Ctrl+Alt+J / Command+Option+J. This action will not only create a copy of the layer, but also pre-open the new layer dialog box, in which we can name the layer before adding it to the panel. Name the layer Apply Image, then click OK to exit the dialog box:
New Layer Dialog Box
If we look again in the Layers panel, we can see that a copy of the image has appeared on a new Outer Channel layer located above the Background layer. It's always better to give your layers descriptive names, which is what we did, otherwise you can easily get confused with the generic names that the program itself gives to layers, such as "Layer 1", which will not tell us anything about the purpose of the layer:
A copy of the image appears on the "Outer Channel" layer
As I mentioned at the beginning of the tutorial, we usually select blending modes in the Layers panel because we tend to apply them to an entire layer. The blend mode selection button is located on the left top corner Layers panel. As an example, I'll now quickly change the Blend Mode of the Outer Channel layer from Normal (the default) to Soft Light:
Change the blending mode to “Soft light”
Changing the mode shows the interaction of two layers - the “Outer Channel” layer and the underlying background layer. The Soft Light mode belongs to the group of contrast enhancement modes, as it increases the contrast level of the entire image, which is what we see in our photo. Color saturation has also increased slightly:
Image after changing the blend mode to Soft Light
I'll change the Blending Mode back to Normal to return to the original settings:
Changing the blend mode back to Normal
So, if changing blend modes in the Layers panel affects how layers interact as a whole, where does working with individual color channels affect and how do you use blend modes for channels? To answer the first part of the question, we need to take a closer look at the Layers panel. We will see that it is located next to two other panels - Channels and Paths, each of which has its own icon. Click on the Channels panel icon:
Click on the channel bar icon
This action will switch to the Channels panel, where we can see the individual color channels: Red, Green and Blue, which make up our image. The RGB channel at the very top is not really a channel. It is the result of merging the red, green and blue channels, or in other words, this is how we see a full color image (each color in the image is made up of a combination of red, green and blue):
In the Channels panel we can find the individual color channels
We can select an individual channel simply by clicking on it. I'll click on the red channel to select it:
Red channel selection
Selecting the red channel temporarily disables the green and blue channels and allows us to see only the red channel in the document window. Photoshop displays color channels as grayscale images, and each channel represents an image with different shades of gray. This is what my red channel looks like in the document window. If you compare this version of the image to a full color image, you will notice that areas containing red in the color image are lighter in grayscale, while areas containing little or no red are lighter. look darker:
Halftone image after selecting the red channel
Green channel selection
The document window now displays the green channel as a grayscale image. Note that it is significantly different from the red channel. Again, if you were to compare this image to the color version, you would notice that areas containing a lot of green appear lighter in grayscale, while areas with little or no green appear darker:
Halftone image after selecting the green channel
Finally, I'll click on the Blue channel in the Channels panel to select it, which will temporarily disable the Red and Green channels:
Blue channel selection
Now we have a blue channel in the document window, and again the grayscale image is different from the red and green channels. This time, the more blue the area in the color image contains, the lighter it is in the grayscale image, and conversely, the less blue the area in the color image contains, the darker the area in the grayscale image. When you soon select an individual color channel in the Outer Channel command dialog box, keep in mind these three versions of color channels, represented by grayscale images in different shades of gray:
Halftone image after selecting the blue channel
To get to the full color version of the image, click on the RGB channel at the very top of the channels panel. This action will return all three color channels to work:
Mixed RGB channel selection
And again we see a full color image:
A full color image has reappeared in the document window
External Channel command
Now that we know that color channels are located in a separate panel and each of them represents a grayscale image, let's answer the second part of the question - how we can apply blend modes to them. You may have noticed that the Channels panel doesn't have a Blend Mode tab like the Layers panel does. In fact, we don't need to work with the Channels panel anymore, so let's go back to the Layers panel by clicking on its name (Layers):
Switch back to the layers panel
To apply blend modes to individual color channels, we use the Outer Channel command. To do this, select the menu bar “Image” at the top of the screen, then from the list - “External channel” (Apply Image):
Select “Image” > “External Channel” (Image >ApplyImage)
This action will open the External Channel command dialog box. If you've never worked with it before, it may seem a little intimidating, but it's actually quite simple. In reality, we will only use two parameters - Channel and Blending:
Channel and Overlay options in the Outer Channel command dialog box
The “Channel” parameter is responsible for selecting the channel that we want to use for work. By default, the RGB channel is selected, which, if you remember, is the blend channel located at the very top of the Channels panel (the result of merging the red, green and blue channels to create a color image). The “Overlay” parameter is responsible for selecting the blending mode we need. If we leave the Channel option with the RGB channel selected and just change the blend modes, we'll get the same result as choosing a blend mode in the Layers panel. For example, I'll select the Soft Light blending mode in the External Channel command dialog box (Channel option - RGB):
Leave the “Channel” parameter with the valueRGB and change the blending mode to “Soft Light”
You can clearly see that my image is no different from the one I got when I selected the Soft Light blend mode in the Layers panel earlier in our tutorial. The same increase in contrast and color saturation occurred:
The Outer Channel command's Blending option works the same as the blending modes in the Layers panel when a channel is selectedRGB
But things get interesting when, instead of the RGB channel, we select any of the three separate color channels. I'll leave the blend mode at Soft Light and change the Channel from RGB to Red. This way I'll only overlay the red channel:
Red channel selection
This time the result is completely different from the previous ones. We still see an overall increase in contrast due to the Soft Light blend mode working, but thanks to the interaction of the red channel's grayscale image with the blend mode, we get a different effect. The girl's skin looks much lighter than before. The same thing happened with her hair, with her red top and areas of red, orange and yellow on her jacket. Essentially, everything that contains a lot of red in the image now looks lighter, while areas that contain little or no red, such as the blue and green areas of the jacket, look darker than before:
The effect of the interaction of the red channel with the Soft Light blend mode
Let's see what happens if I change the Channel value to green (the blend mode is still Soft Light):
Switching from red channel to green
By selecting the green channel, we have another option for applying the effect. This time, areas containing a lot of green became lighter, while areas with a lot of red or blue became darker. The most distinct change occurred with the girl’s skin, which became darker and more contrasting than when choosing the red channel:
Interaction of the green channel with the Soft Light blend mode
Now I'll change the Channel value to blue:
Blue channel selection
In this case, we got a third version of the image, when the areas with blue became lighter, and the areas with red or green became darker. These variations of the effect wouldn't be possible (at least not without a lot of effort) if we didn't have access to individual color channels using the External Channel command:
Each color channel gives us its own option for applying the effect.
Of course, we're not limited to using just the Soft Light blend mode when working with our color channels. We can choose any of the blend modes, just like we would in the Layers panel. I'll leave the Channel at Blue and change the Overlay to Overlay:
Selecting the Overlay blend mode for the blue channel
Like the Soft Light mode, Overlay is a mode that enhances the contrast in the image, but to an even greater extent:
Interaction of the blue channel with the Overlay blending mode
And here’s what the “Overlap” mode will look like when you change the channel to “Green”:
Interaction of the green channel with the Overlay blend mode
And this is what the red channel looks like in Overlay mode:
Interaction of the red channel with the Overlay blend mode
The red channel image looks too saturated when interacting with the Overlay mode, but we can easily mute the colors if necessary by reducing the opacity of the overlay. You'll find the Opacity option directly below the Blending option in the Outer Channel command dialog box, and it works the same as the Opacity option in the Layers panel. The default value of the parameter is 100%. I'll reduce its value to 60%:
Lower the opacity to reduce the intensity of the overlay effect
By reducing the opacity, we returned some of the highlights and shadows to the image:
Image after reducing the opacity of the Overlay blend mode
If you want to compare the processed and original images, simply disable the option " Preview» (Preview) located on the right side of the dialog box. This action will hide the application of the effect and allow you to see the original image in the document window. Select the Preview option again to return to working with the effect:
Turn on and off the Preview option to compare the original and processed images
You will often notice, especially when processing photographs of people, that the Soft Light and Overlay modes are the most successful for processing, but others useful modes Overlays like Screen and Multiply are also worth trying. Screen mode brightens everything in the image, while Multiply mode darkens everything. Try applying these modes to three color channels to see the results, then adjust the intensity of the effect by increasing or decreasing the opacity value. For example, in my case, I set the Channel to Green, Blend Mode to Multiply, and lowered the Opacity to 40%:
"Channel" - Green, "Overlay" - "Multiply", "Opacity" - 40%
As a result, the image became darker and more detailed:
The Multiply blend mode is good for darkening an image. Try Screen mode to brighten it up
When you are happy with the result, click OK to exit the External Channel command dialog box. You can then again compare the processed image with the original one by clicking on the layer visibility icon (in the form of an eye) located to the left of the “Outer Channel” layer name in the Layers panel. Click the icon once to make the layer temporarily invisible and view the original image. Click on the icon again to return the “Outer Channel” layer to visibility:
Toggle layer visibility on and off to compare the final result and the original image
And so we did it! We learned how to apply blend modes to individual color channels using Photoshop's Outer Channel command!
Understanding what you see in each channel provides you with the knowledge to create complex highlight areas and fine tuning 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 an image using a regular laser or inkjet printer, you won't need it. 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.
Lab Channels
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 in new document, and then with 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.
Multi-channel 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!
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. On this moment 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 as 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 and are therefore 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 source image color 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.
Layers are currently the most powerful tool for working with photographic images. When you edit a photo, whether in Photoshop or Paint Shop Pro, you can't do without multiple layers of the image. Sometimes more complex layers are used - custom layers, effects and masks based on layers. Layers are everywhere. And the question involuntarily arises: how did users manage without them before?
The answer is simple - using channels. You can easily spot a Photoshop veteran by the fact that he uses the Channels palette as often as the Layers palette. But this should not be regarded as old-fashioned. Rather, this is evidence of professionalism, since the use of channels opens up wide opportunities.
So, what is a "channel". The standard definition - "a two-dimensional array of information, usually 8-bit" - is unlikely to clarify the situation. Therefore, let's take a closer look at the two main types of channels - color information and alpha channel - from the point of view of their practical application.
Color channels
The easiest way to see color channels in action is to use Photoshop's Channels panel. Open regular 24-bit photographic image in RGB. In the channel palette you will see 4 layers, each with its own icon: RGB, Red, Green and Blue. If you click on RGB, you will see the image that you usually see - composite and full color. For each of the other channels, a grayscale version of it is displayed. The keyboard shortcuts Ctrl+1, 2, 3 allow you to view each of the color channels separately, and Ctrl+~ - a regular composite image.
The full spectrum of RGB colors is created from the red, green, and blue color channels, where they are represented in a gray scale.
To understand what information is displayed in the Layers palette, it is worth observing the channels when working with a test image of a rainbow gradient (in other words, an image of all the colors of the rainbow). In a grayscale image that represents a channel, each of the pixels can represent one of 256 values. You will see that the red part of the rainbow when viewed in the red channel will be white. The yellow stripe of the rainbow will be white in the red and green channels, but will be black, i.e. absent, in blue. In fact, the rainbow image shows that the full spectrum of 16 million colors can be obtained by combining values from 0 to 255 for red, green and blue (256 x 256 x 256). In our image, the yellow stripe corresponds to large values of the red and green channels and 0 to the blue channel. Photoshop works with an image not by individual pixels, but by channels. In this case, three eight-bit layers - red, green, blue - are superimposed, and we get the final image.
Of course, not all images are created in RGB, but this is not a problem since the channels are very easy to customize for different needs. We can convert our image to a different mode using the Image > Mode command. For Bitmap and Grayscale there is only one channel, which represents 256 values from black to white. In Lab mode there are three channels: A (color value between green and red), B (between blue and yellow) and L (luminance value). Separating color from its brightness can be very useful. Select the luminance channel and convert it to a grayscale image. The result will be much better than if you converted the scanned RGB image.
The Lab color model can be very useful. But still the most important, after RGB, is CMYK. This model is print oriented. Convert the rainbow image to CMYK. The first thing that catches your eye is the sudden change in some colors. The fact is that CMYK does not support many pure RGB colors. The second difference is that four color channels have appeared: Cyan, Magenta, Yellow, Black (turquoise, purple, yellow, black). Look at the yellow stripe of the rainbow in the yellow channel - you will see that it is represented by black.
In the CMYK palette, the channels represent the ink colors used in multi-layer, four-color printing.
This mode differs significantly from RGB because Photoshop has to work with ink colors that combine with each other in a subtractive manner (summing all the colors together results in black). In RGB, on the contrary, the principle of addition is applied, and the superposition of all colors will produce white. But, by and large, all color models are similar to each other. And Photoshop can recreate the full gamut of any of them with no more than four eight-bit channels, each of which has no more than 256 values (or 65,536 values if you really want to and go to Image > Mode and choose a 16-bit channel).
Channels are the primary tool for working with color, so it's worth looking at the Channels panel occasionally to learn how Photoshop creates different colors. This is especially true when working with a CMYK model that is designed for printing. When working with RGB, what you see on the monitor does not always correspond to what will come out when printed. Although the values of each channel reflect this. Moreover, if you want to replicate an image, you need to consider factors such as dot blurring and gray component replacement. This means that accuracy in working with color channels is very important, since color separation subsequently depends on it.
Channels are useful for more than just CMYK printing. You will find their use in RGB as well. Let's say you can edit not the entire image, but a separate channel. When adjusting color, it is worth looking at individual channels to identify defects in the scanned image. For example, if you find a blurred or misaligned area in the red channel, you can correct this issue by using a sharpening filter or adjusting the levels.
And in order to create some special effect, you can apply an artistic filter to one of the channels. In any case, you can immediately see the result of your actions on the composite image - just make the RGB channel visible. Just remember to select the desired color channel again later if you continue to work on it.
The channel merging function provides ample opportunities. For example, using the Apply Image command, you can overlay information from any channel of another image of the same dimensions onto the RGB channel of our image and customize this effect by changing the opacity and color mixing mode. The Calculation command allows you to select two layers and create a new layer, selection, or document. If you use the subtractive color mixing mode, you will select areas of the image that have changed compared to the original.
With the introduction of the Channel Mixer command and custom layers in Photoshop 5, the ability to combine channels has expanded. The channel mixer feature is used only for individual images and allows you to customize each channel by adding information from other channels. With its help, you can create special effects, swap channels, and correct color defects in scanned images. It's also ideal for creating "tinted" and high-quality halftone images (and you can control how each color channel is converted to grayscale).
Channel blending is very helpful when converting color images to grayscale.
Adjusting colors using channels will undoubtedly come in handy. But the most common way to use them is to work with secretions. Often, image elements are much clearer in a single channel than in a composite image. For example, selecting a bear in the bear.psd training file is much easier in the blue channel.
Alpha channels
Once you've created a selection, you'll probably want to save it. This can be done in the alpha channel. To do this, use the “Selection > Save Selection” command or the “Save Selection as Channel” icon in the Channels panel. After this it appears new channel, in which selected pixels are displayed in white, unselected pixels in black, and blurred pixels at the border of the selection in shades of gray.
By double-clicking on the channel icon, you can rename it and set the color it will appear in the composite image. You can work with the alpha channel like any other, for example, adjust levels or apply filters. Moreover, you can edit this channel using a brush - for example, paint over defects. When you are satisfied with the result, use it. To do this, convert the alpha channel into a selection using the Selection>Load Selection command, the Load Channel as Selection icon in the Channels panel, or simply by Ctrl-clicking on the channel icon. If you have multiple alpha channels, you can create more complex selections. For example, you have selected and converted an image of a person and bushes in the background to alpha channels. You can select only the bushes if you select them and load the channel as a selection using the "subtract" option. Keyboard shortcuts will speed up this procedure: click on the icon while holding Shift+Ctrl - this will add a new area to the selection, Alt+Ctrl+click - subtract from the selection, Alt+Shift+Ctrl+click - will give the intersection of two selections.
Alpha channels can be saved and loaded as selections.
Once you've converted the alpha channel to a selection, it will immediately appear on screen and you can transform it, copy it to a new layer, or edit it in any way. The flickering dotted line along the edge of the selection does not very accurately indicate its boundaries - you need to take this into account. It only displays alpha channel pixels that have gray intensity below 50%. For most selections this makes little practical difference. But the advantage of the alpha channel is that it allows you to work with 256 levels and thus create complex, variable transparency masks.
How can you use these masks? Here are some examples (it's actually easier to do than it looks when you read it). Click on the "Create New Channel" icon and create an empty alpha channel, then apply a gradient to it and select the composite channel again. Ctrl-click on the alpha channel icon. Now apply any artistic filter to the created selection. Its effect will depend on the halftone values of the gradient mask. It will seem that the photograph is gradually turning, for example, into a painting.
The alpha channel can be used as a variable opacity mask.
Another example: create a copy of the alpha channel from a text selection and apply a Gaussian blur to it. After that, subtract the original channel (Alt+Ctrl+click) and you will get a new channel that will show only the noise surrounding the text. Now select this area in the composite or any of the color channels. You can adjust the levels so that the highlight glows, or even remove original text and the glow will appear to be part of the photo.
You have the foundation, now experiment - you can create many effects using shadows, extrusions, vignettes, etc. Surely, if you get serious about this, you will need the ability to save alpha channels with your file. But Photoshop's capabilities in this regard are surprisingly limited - the program supports saving the alpha channel in a tiff file or in Photoshop itself (but the number of channels in a file, including color ones, is limited to 24). This won't pose a problem if you only work in Photoshop. But the presence of an alpha channel can significantly affect the export of a file to one of the standard formats. For example, when saving for the Web, in the dialog box that appears, you can use the alpha channel as a mask to adjust the quality and, accordingly, the size of jpg and gif files. Using the alpha channel, you can draw attention to a certain part of the image that will be of the highest quality. The quality of other areas of the image will deteriorate, but this will significantly reduce the overall file size. Alpha channels are also useful when working with transparency. Create an alpha channel that covers the area that you don't want to be visible in the web version, and Ctrl-click to select that area. Now call the Transparent Image Export Wizard and select gif. The selected area will become transparent in the final file, and you will be able to avoid making irreversible changes to the original. The wizard allows you to export the image to a png file that supports 24-bit color and 8-bit transparency. If you create an alpha channel with radial gradient, then you will receive a vignette. Unfortunately, few programs support 32-bit png files with transparency. The only exception is, perhaps, Director 8.5.
With the ability to add spot colors in CMYK, alpha channels are also useful for high-quality printing. Select the area of the image that you want to print as a color fill, and then use the New Spot color command from the Channels panel menu. When you set a color, click "Custom" and select a color, for example from the Pantone library.
Please note that adding a color fill is not as simple as it seems. The image on the screen, as you know, does not always correspond to what is printed. Ink colors often cannot be represented in RGB and Photoshop simply shows what it thinks the image should look like when printed layer-by-layer. If you save your file in DCS 2.0 format and load the EPS composite image into a professional publishing program, you can color separate the four primary colors and custom color files you created.
The custom color channel allows you to display ink colors that are not included in the CMYK palette.
There's no doubt that channels play a very important role in photo editing, from adjusting colors and highlights to working with images for the web and high-quality prints. But time moves on, and layers often produce better results than channels. Having created a selection, copy it to a separate layer - and you can work with it independently, and, if necessary, return to the original version. The same goes for many other effects that were previously created using channels. Today, custom layers, effects, and layer-based masks do a better job of accomplishing this task.
The canal system was also improved. So, although in many areas channels are gradually being forced out of use, they are unlikely to disappear completely. If only for the simple reason that layers are created based on channels. Strictly speaking, a layer is a set of independent color information channels and alpha channels, one of which controls transparency, and the second acts as a layer mask. The same goes for custom layers, which are essentially alpha channels through which color is adjusted.
Photoshop, like any other photo editor, creates an image on the screen by processing values from the color and transparency channels of the layer. And so, one by one, all the layers from the background to the foreground. Of course, in reality, working with an image is much more complicated - the program calculates color mixing modes, opacity, settings, etc. But it's based on a step-by-step mathematical process. The program does not see the image; it works with the data array of each channel. Any photo editor “thinks” in terms of channel categories. This is a habit worth adopting as a professional user.
Color information in Photoshop is stored in what are 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 dot, the large quantity The color of this 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.
RGB channels
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 flowers 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 is yellow and the dot is 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.
CMYK channels
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 CMYK is not present in the 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 a certain color participates in the formation of the resultant, 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 professional use Photoshop programs and especially if you work in organizations that produce printing products, you will certainly come across such a concept as 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.
Channel masks
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.
