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Filtering Individual Channels
If you need to apply a filter to an image (for instance the Unsharp Mask filter), and the correction that you are going to make is very slight, you may want to try applying the filter to each channel individually. This can give you more precise and satisfactory results.For an example, I’m using this great photograph of a Manhattan office building under construction, shown in Figure 53-4. As you look at the photograph, notice how it looks a bit blurry. The edges can really use a good sharpening.
Figure 53-4: This photograph looks a little blurry.
After applying the Unsharp Mask filter to all the channels at once, Figure 53-5 shows the best results that I can get. (You may have to look closely because these filter corrections are very slight.)
Figure 53-5: The photograph is better, but it’s not good enough.
So instead of sharpening all the channels at once, I turned to applying the Unsharp Mask filter to each channel individually. Figure 53-6 shows the great results with sharp edges.
Figure 53-6: Applying the Unsharp Mask to each channel really sharpens the photograph.
You can also create some really cool effects by applying a filter to only one channel. Take a look at Figures 53-7 and 53-8. In each figure, the upper image shows the filter applied to the entire photograph. In the lower image, the same filter has been applied to only one channel.
Figure 53-7: The Filter>Stylize>Glowing Edges filter applied to the entire image (top) and to only the red channel (bottom).
Figure 53-8: The Filter>Artistic>Sponge filter applied to the entire image (top) and to only the green channel (bottom).
