Tuesday, August 6, 2013
Blending Channels Part II
More on how and when to use this powerful Photoshop tool
|This Article Features Photo Zoom|
You can enhance a channel before (or if you use channels as layers after) blending it with another. Use any adjustment method that makes the data better to blend with. As you're blending with black-and-white images, Curves is usually all you need, for it offers the most precise control of tone. For instance, you might increase the contrast of an image before using it to blend with. If you're using the channels-as-layers method, all you have to do is group a Curves adjustment layer to the new layer being used to blend with. The contrast of the overlying layer can then be fine-tuned as the blend with the underlying layer is occurring. This way you don't have to guess how much contrast needs to be added before blending, instead you see how much contrast to add while the blend is occurring.
Constraining The Effect
While blending channels may solve problems that other adjustment methods can't, they may also produce new problems.
Multiply multiplies the value of the pixels on both layers and then divides by 255. It's like registering two identical transparencies on a light table.In a great many cases, if the tonal distribution of a single channel is substantially altered using another channel, color may shift in an unintended manner. If this happens, simply make an additional adjustment to eliminate any side effects. There are times when the color shifts you encounter will be non-uniform (more in some areas than others), which may lead you to making more complex corrections than you had anticipated.
If the problem solved with channel blending and the resulting side effects lie in different areas of the image, consider masking away the side effects rather than correcting them. There are several ways of masking the side effects of channel blending from selected areas. One, simply brush them away by painting with a black brush on a layer mask. Two, use a contrast mask to hold back the effect from highlights or shadows. Three, use the Blend If function in Layer Styles; by sliding the black arrow to the right or the white arrow to the left, you drop out the effects from values below or above them—by holding the Option key (Command on PC), you can split the sliders to fade the effect more smoothly.
|4) Before blending channels, the image contains a severe color cast. 5) Lack of detail in the Red channel is the problem. 6) After blending channels, a realistic color balance is restored.|
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