Sometimes it’s better to edit individual channels rather than the composite image. Mediocre flatbed scanners often reproduce an image that is slightly soft or out of focus. You may want to counteract that effect by applying an Unsharp Mask filter. Before you do, you should examine each channel separately. You may find that the Blue channel contains a lot of garbage — artifacts, dithering, and other nasty crud. Blue channels are notorious for acquiring this junk, so try to avoid applying an Unsharp Mask filter on this channel unless you really want to accentuate what’s already ugly.
Instead of applying the Unsharp Mask filter on Blue channels, select the Red and Green channels and then choose Filter-->Sharpen-->Unsharp Mask. Similarly, you can apply a Gaussian Blur filter to a channel to soften the unsightly pattern (called a moiré pattern) caused by scanning a halftone. While Unsharp Mask and Gaussian Blur are a couple of your corrective filters that you’ll use frequently, I also find it useful to apply a special-effect filter to individual channels as well.
Sometimes applying a filter to the composite image produces an effect that’s, well, overdone. Applying the filter to one or two channels can produce an effect that is subtler and less inyour-face. Using individual channels can also be useful for applying filters that produce monochromatic images, such as the Graphic Pen or Photocopy filters. If you apply the filter to the entire image, you get a black-and-white image. If you apply it to an individual channel, you retain some color. You can select a color channel and then edit that channel by using a painting or editing tool to paint in the image. Keep these facts in mind:
- Painting with white adds the color channel’s color at full intensity in the composite image.
- Painting with black removes the color in the composite image.
- Painting with a value of gray adds color at varying levels of intensity in the composite image.
For example, if you paint with white on the Blue channel in an existing image, Photoshop adds more blue to the color composite image. But if you paint with black, Photoshop adds yellow to the image because when you remove blue, what’s left is the opposite, or complementary, color — yellow. To perform this channel magic, select the Brush tool and then choose your desired brush size from the Options bar. Choose your desired color in the Color palette. Select the channel you want to edit in the Channels palette. You can see the results by selecting the composite channel in the Channels palette. The results are a little different if you try this technique on a blank CMYK canvas. When you paint with black on the Cyan channel, your composite color image displays cyan. When you paint with white, you get nothing.
Instead of applying the Unsharp Mask filter on Blue channels, select the Red and Green channels and then choose Filter-->Sharpen-->Unsharp Mask. Similarly, you can apply a Gaussian Blur filter to a channel to soften the unsightly pattern (called a moiré pattern) caused by scanning a halftone. While Unsharp Mask and Gaussian Blur are a couple of your corrective filters that you’ll use frequently, I also find it useful to apply a special-effect filter to individual channels as well.
Sometimes applying a filter to the composite image produces an effect that’s, well, overdone. Applying the filter to one or two channels can produce an effect that is subtler and less inyour-face. Using individual channels can also be useful for applying filters that produce monochromatic images, such as the Graphic Pen or Photocopy filters. If you apply the filter to the entire image, you get a black-and-white image. If you apply it to an individual channel, you retain some color. You can select a color channel and then edit that channel by using a painting or editing tool to paint in the image. Keep these facts in mind:
- Painting with white adds the color channel’s color at full intensity in the composite image.
- Painting with black removes the color in the composite image.
- Painting with a value of gray adds color at varying levels of intensity in the composite image.
For example, if you paint with white on the Blue channel in an existing image, Photoshop adds more blue to the color composite image. But if you paint with black, Photoshop adds yellow to the image because when you remove blue, what’s left is the opposite, or complementary, color — yellow. To perform this channel magic, select the Brush tool and then choose your desired brush size from the Options bar. Choose your desired color in the Color palette. Select the channel you want to edit in the Channels palette. You can see the results by selecting the composite channel in the Channels palette. The results are a little different if you try this technique on a blank CMYK canvas. When you paint with black on the Cyan channel, your composite color image displays cyan. When you paint with white, you get nothing.
Using Painting and Editing Tools with Photoshop Channels
![Using Painting and Editing Tools with Photoshop Channels]()
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