Adobe Photoshop is one of the most popular packages for processing bitmap graphics. Despite the high price, up to 80% of professional designers, photographers, and computer graphics artists use the program. Due to its enormous functionality and ease of use, Adobe Photoshop has a dominant position in the graphics editor market.
Increase the sharpness and contrast of a photo using channels in Photoshop
About Adobe Photoshop
Topic 3. Photo enhancement.
How to sharpen photos in Adobe Photoshop using channels.
The third topic of the Photoshop course is completely devoted to methods of visually enhancing photography. The previous lesson was devoted to the issues of correcting the sharpness of photos using Adobe Photoshop. Three basic methods were considered. Or, as they are also called, explicit functions for working with the sharpness of photos.
As you may have noticed, the use of these methods quite seriously changes the appearance of the image. In particular, colors. With careless manipulations (for example, with channels), the color gamut of the photo can change significantly.
You should not refuse to use the same curves or levels. These are powerful tools. But each method has its own place. Let's turn to more "delicate" methods of processing.
The techniques for sharpening photographs discussed in this Photoshop tutorial focus on maximizing the preservation of the color information of the original image.
Some theory
The previous lessons in our Adobe Photoshop course helped you understand the concept of image sharpness or contrast. And also learn the basic methods of visual enhancement of photography.
The presented material is more than enough for “everyday” photo processing (in the field of sharpening). However, as you noticed, any manipulation to change the image entails changing its color gamut. What to do when color is not only important, but very important, but at the same time the task is to increase the contrast of the photo.
It is in such cases that the ways of correcting sharpness using channels are justified.
You can read about channels in the article "Selecting with channels in Adobe Photoshop".
To work effectively, we need to return to the topic of Photoshop color spaces. About what a color space is, and how color is represented in computer memory, the conversation was conducted in the lesson "Selecting color ranges in Adobe Photoshop". The theoretical part of the lesson contained information about the so-called "cubic" coordinate systems - CMYK and RGB.
If we remember, both of them have a significant drawback: they encode fewer colors than the eye can perceive. But they are practical - on their basis the entire mathematical system of color representation is built. The LAB system is fundamentally different. It is NOT practical (information is not displayed with its help). But on the other hand, it can be used to describe more colors than a person can see.
This color coding system is used in Photoshop as an "intermediate" color space. Primarily for subtle color correction.
It's easy to imagine what the LAB color space is. This is a set of "color circles" strung on the axis of "brightness". It looks like a cylinder we are used to. The coordinates on the circles are set along two axes. Axis A - from green to red. B-axis - from blue to yellow.
The figure shows a graphic representation of the LAB space (in a truncated, spherical form - only visible shades). And a comparison of the number of described colors compared to CMYK and RGB.
Practical part
As a practical example, let's take a familiar picture of a forest lake.
Sharpening by blending channels (RGB or CMYK)
One of the previous tutorials was devoted to sharpening by changing the appearance of a photo by overlaying layers. However, the copy of the image to the layer already contains color information. And multiplying or adding color coordinates often does not give the best result - the shades can change significantly.
At the same time, if you superimpose a layer in “grayscale” on a color photo and apply blending modes from the “sharpen” group, the colors of the photo that we get will look more like the original. Which is pretty good.
The question arises: where to get a copy of the image in grayscale. The first option was completed in the previous lesson. Just copy the layer.
However, this is often not the best way. For example, in our case, there are several zones with their own specifics. These are water, sky, grass on sand and foliage. Ideally, each of them needs a different approach.
Now let's remember the lesson "selection using channels". Each image has at least three color channels. They are displayed as grayscale images. If you look at each channel separately, the differences are visible to the naked eye. Thus, having selected one or another channel, we can use it as an overlay layer to increase the contrast. At the same time, taking into account the specifics of the channels, we will affect certain color zones of the image.
Let's start. In order to work with overlapping channels, you must select one of them as a "donor". To do this:
- Using the " Window " menu, call the " Channels " palette. It docks to the Layers Palette, which is very convenient.
- To the left of each icon there is a visibility (eye) icon. Alternately including the visibility of only one channel, choose the one that suits your goals.
- Press CTRL + A to select the entire content of the channel. Or any of the selection methods is the necessary part. Copy it CTRL + C .
- Go to the layers palette and create a new layer. This can be done through the menu in the upper corner of the palette, the general menu of Photoshop (the " Layers " group) or the keyboard shortcut Shift + CTRL + N .
- Go to the created layer, paste the channel information on it.
- Further, if desired, modify the channel with levels or curves to obtain the most contrasting image in black and white
- After that, feel free to select the blending mode and transparency of the new layer
Note that different channels and different blending systems will give different results. Do not trust only the usual methods. It's worth checking all the available ones. This is the foundation of training in fine-tuning photographs.
After you have overlaid the desired channel and selected a blending method, you can finalize the image.
Final work is also done on a black and white layer. The simplest thing is to change the saturation (contrast) of the black and white layer using levels. You can also use curves or other tools.
If the "Preview" option is selected in the tools, the result will be visible in "real time".
Practical advice :
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If you need to emphasize contrast, for example, water or sky, try not to select the blue channel. It will be just white in the right places. Differences in shades are guaranteed by other neighboring colors (red, green). The same goes for foliage (we work WITHOUT green channel), fire (without red), etc.
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By choosing a "lighter" channel, you get a brighter contrast. Darker - sharpens with darker.
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After choosing a channel, play with the overlay methods. The results can be quite satisfying.
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After setting the preliminary blending parameters, always modify the black and white layer. This helps to achieve results that are close to ideal.
Sharpening in LAB color space
Now it's time to pay attention to the LAB color space. It is interesting to us because one of the coordinate axes is responsible not for the color, but for the brightness of the pixels. By changing its characteristics, we DO NOT change the base color. Its saturation changes (from dark to light). Thus, the overall gamut of the photo remains similar to the original.
This property is essential for subtle and accurate sharpening. It is enough to make the brightness channel more contrast, and our image becomes clearer.
How to implement it in practice is described below.
First, we need to translate the image into the LAB system. It's simple.
From the " Image " - " Mode " menu, select the LAB item. Done.
Now we need to modify the luminance channel. For this
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Go to the channels palette
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Make the channel " Brightness " active
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Use curves to darken the dark areas and highlight the light ones. How to use curves is described in Three Easy Ways to Sharpen.
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Click OK .
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Turn on all channels, go to the layers palette and enjoy the result.
However, it is not always convenient to work with a channel without seeing the result in real time. It can be fixed. The algorithm for working "with preview" looks similar in its first part.
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From switching to the LAB system to choosing a channel, proceed in the same way
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Next, turn on the visibility of all channels. In this case, only the " Brightness " channel is left active. We see a color image.
The second method: call the " Curves " tool and in its dialog box select work with the " Brightness " channel. This is probably easier.
Note : LAB space is absolutely not suitable for printing or web. After completing the correction, switch to RGB or CMYK. This is done in the same way through the menu " Image " - " Mode ".
The advantage of adjusting the sharpness in the LAB space is the preservation of the overall gamut of the picture.
Undoubted minus - difficulty with working in part of the image: removing information from part of the channel will lead to irreparable loss of information on this fragment.
The Topic of Article: Photoshop tutorials. Topic 3. Improving photos. Part 4. How to sharpen photos in Adobe Photoshop using channels.
Author: Jake Pinkman | 
