Per request, I'm posting the steps to utilize a good channel within an image.
Step 1
Have the LAYERS and CHANNEL palettes open next to your image.
Step 2
It's much easier to see channels when they are grayscale. By default, Photoshop shows channels in Red, Green, and Blue. To view the channels in grayscale:
• Locate PREFERENCES on the MAIN MENU.
• Select DISPLAY AND CURSORS and
uncheck the box for "Display Color Channels in Color"
Step 3
On the CHANNELS palette, click once on the layer you want to use.
In this example, I'm going to select the BLUE channel as it has the most image information.
Step 4
From the MAIN MENU, choose "SELECT", then from that menu choose "ALL". You should see the "marching ants" around the border of your image indicating it's been selected.
Step 5
From the MAIN MENU, choose "EDIT", then from that menu choose "COPY". This step copies the channel to the clipboard.
• Click once on the "RGB" channel in the CHANNELS palette.
Step 6
From the MAIN MENU, choose "EDIT', then from that menu choose "PASTE". This step will paste the channel into a new layer in the LAYERS palette.
• Set this new layer's OPACITY to "LUMINOSITY"
Step 7 (optional)
At this point you can see the "good" blue channel with the color from the original showing through. This is a much easier fix. For example, in the image below, I've added a transparent layer "layer 2", with it's OPACITY set to "Color". I used the eyedropper tool to select colors and then painted on the transparent layer. Now it's just a matter of cleaning up the smaller damaged areas.
That's it.
