This seems like it should be a relatively simple task but I can’t sort it out.
If I have a layer that is just black->gray->white colors (say for example a gradient). Is there a way to make that layer be the mask for another?
I know you can create new layer and draw onto it, but it doesn’t seem you can copy into it or use another layer as the mask.
Basically I’d like to create an alpha channel for an image or layer from another image/layer.
Basically I’d like to create an alpha channel for an image or layer from another image/layer.
I assume what you really want to do is not create an Alpha Channel, but change the transparency of a layer. If what you want to do is use a grayscale image to mask (change transparency of) another layer:
[ol]
[li]Select and copy the contents of that gradient layer that you want to use as a mask[/li][li]Create a Layer Mask on whichever layer you want to have masked (Select layer you want to mask in the Layers Palette, then choose Layer Menu>Layer Mask>Reveal All)[/li][li]Paste the gradient layer into your new layer’s Layer Mask (making sure the layer mask side of the layer is selected and not the pixel side of the layer)[/li][/ol]Wherever your Layer Mask is black, it will make your layer 100% transparent, wherever your Layer Mask is white, it will make your layer 0% transparent (or fully opaque), and every grey in between will be accordingly transparent. Be aware that when a layer has a Layer Mask, you can alter either the pixel side or mask side of the layer… make sure you click on the correct thumbnail in the Layers palette so you are altering the appropriate side.
That’s what I was trying to do, but when I paste it just creates a new layer with the gradient, it doesn’t paste into the mask. I have Photoshop CS2. Is this a version issue or is there something I’m not doing correctly?
Thanks!
Oh, you’re completely right. Terribly sorry. To paste an image into a Layer Mask, you have to select the Layer Mask, then in the Channels palette, select the Layer Mask alpha channel, and paste it into there. It’s a long way around, but that’s the official way to paste into a Layer Mask. Don’t forget to select the RGB channel (or whatever your composite channel is) before leaving the Channels palette.
That Layer Mask alpha channel only appears when you have a Layer Mask chosen.
Sorry to point you in the wrong direction at first.
By the way, another way to do this would be to paste the mask image into the Quickmask Mode, then use that selection to fill your Layer Mask with black. If you want to try it that way, here are the steps:
[ul]
[li]Copy the mask image
[/li][li]Create a Layer mask in the layer you want to mask, choosing “Reveal All”
[/li][li]Enter Quickmask Mode by pressing Q
[/li][li]Paste the mask image into the Quickmask. You should see a red overlay of your mask image.
[/li][li]Leave Quickmask Mode by again pressing Q
[/li][li]You should now have a selection. Make sure the Layer Mask is selected
[/li][li]Fill the selection with black
[/li][li]If needed Select All and invert the colors
[/li][/ul]
There are two ways to view selections in Photoshop. The first is called Standard Mode and is the default way of viewing them. This is the vibrating lines you’re used to seeing. The second is Quickmask Mode, where your selection is shown as a reddish overlay. Two ways of viewing the same selection. There’s also a button to toggle between the two modes at the bottom of the Tools palette.
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