How to create alpha mask from an image in Photoshop CS/8

Question

I have a monochrome image, and would like to replace the colour with a gradient.

I assume the best way to do this would be to create a background layer with the gradient, and then apply the monochrome image as a mask. However, I can't for the life of me get this to work. If I copy the image, and then try to paste it into a mask layer, it just creates a new normal layer and pastes it there.

How to accomplish this?

Answer 1

I don't have version 8 anymore, but try this.

1. Select All and copy the image from the layer you want to use as a grayscale mask.
2. Switch to the channels tab of the layers panel.
3. Add a new channel. Paste your image data in that new channel.
4. Click the button on the bottom of that panel labeled "Load channel as Selection" — you will get a marquee selection of the alpha channel.
5. Switch back to the layers panel, click on the layer you wish to apply a mask to and click the button at the bottom of that panel "Add Layer Mask".

That should be all you need. There's probably an easier way, but I can't think of it right now.

Answer 2

Method 1 (Adds a simple gradient):

1. Convert your monochrome image to RGB (Image > Mode > RGB).

2. Double-click the background layer to convert it to a regular layer.

3. Add a new layer below the image (Ctrl/Cmd Click on the new layer icon).

4. Fill that layer with the color gradient.

5. Change the blend mode of the image layer to "Luminosity."

Method 2 (Recolorizes the image):

1. Convert your monochrome image to RGB mode as above.

2. Add a Gradient Map adjustment layer.

Answer 3

I can't really understand what you're trying to do with the gradient, but to paste into a layer mask:

Select the layer with a mask.

Go to Channels and the mask is listed as the bottom channel.