Replace Channel

The Replace Channel transformation takes an input image and splits it into three channels using either the RGB, HSV or HSL color space. It then replaces one of these channel with another image This transformation is useful if you want to apply one or more transformations to one of the channels of the input image and leave the others unchanged.

Amount

The Amount control lets you control how much of the Replace Channel transformation is applied to the input image. You can apply a percentage of the transformation to the entire image, or you can specify an amount mask to restrict the effects of the transformation to only part of the input image.

Channel

This control lets you select which channel you want to replace. You can select the Red, Green, Blue, HSV-H, HSV-S, HSV-V, HSL-H, HSL-S, HSL-L channels.

Channel Image

This control lets you select the image that will replace the specified channel. The image must be the same size in pixels as the input image and must be black and white (either 8- or 16-bit). If no channel is specified, an all white image of the appropriate size is used as a placeholder.

Example: Using Replace Channel to apply transformations to one channel of an image

Suppose you want to sharpen just the HSV-V channel of an image. While this option is already supported by some of Picture Window's sharpen transformations, this example illustrates how to do it using Replace Channel.

The general idea is to extract the channel you want to operate on, in this case the HSV-V channel, apply one or more transformations to the extracted channel, and then replace the channel in the original file with the transformed version. A workflow that accomplishes this might look like this:

1) Open the file you want to process.

2) Insert a splitter after the original image (right click on its thumbnail and select Insert Splitter After from the context menu).

3) In one of the branches insert an Extract Channel transformation and select the channel you want to operate on (in this example HSV-V). Then add the transformation(s) you want to apply to this channel (in this case Bilateral Sharpen).

4) In the other branch, insert a Replace Channel transformation and select the HSV-V channel and set the Channel Image to the Bilateral Sharpen image.

The output image of Replace Channel is now the original image with its HSV-V channel sharpened. This method is much simpler than the alternative using Extract Channel to extract all three channels, applying transformations to one of them and then using Combine Channels to merge the three channels back into a color image.