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Masks & Selections


S

Sark

Power User
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Hi all.

Just a few questions on masks and selections (PS 6).

1...Can I paste a black & white image on to a layer mask to control the transparency/opacity of that layer. I know I can paint on a mask with black & white but I can't work out how to use an image as my layer mask.

2...Is it possible to make a selection of only what is visible through a layer mask.

3...Is it possible to make a selection from a black & white (blurred) image layer so that the blurred (grey) pixels are selected as black pixels of varying transparency. Ultimately I want an alpha channel of the blurred black & white image, but as shades of black on a transparent background.

Many thanks.

Sark
 
1. My method -
Cut-n-paste the image into an alpha channel
Load it as a selection
Apply it as a layer mask

2. ctrl + click the layer mask to load it as a selection

3. Not exactly sure what you are asking. I suspect that #1 might be the start of an answer, then it's a matter of possibly inverting or blending modes or something...?
 
Stroker ,thanks for posting.

As I'm not at my PC at the moment just one question

How do I apply the selection as a layer mask?

Cut-n-paste the image into an alpha channel
Load it as a selection
Apply it as a layer mask

Also, yes it's possible the first two answers will lead me to the third, will check it out tonight.

Thanks again.

Sark
 
To apply a selection as a layer mask, you can use the menus. Or you can use the little shortcut icon at the bottom of the layers palette.

Here is some chat about layer masks, item #6: Building Backdoors.
 
Thanks again.

I suspected I could have figured it out once I was at my PC with PS open, but just wanted to make sure it wasn't a little more complicated.

Will give the link a good look at.

Thanks once more, it's much appreciated.

Sark
 
Stroker, Have been playing around with PS and now have a much clearer understanding of the above, just one question.

How do you Cut-n-paste the image into an alpha channel

My own method is to Duplicate the Document, Convert the duplicate to Grayscale and drag the Alpha channel onto the original document page before deleting the duplicate document.

Is this the accepted method.

Sark
 
Actually, it's more like copy and paste.
In the layer palette, ctrl + a to select all.
Start a fresh alpha in the channels palette.
With the new alpha active, ctrl + v to paste.
Tada.

Works great for visible black & white. If you are copying visible colour, things can get a bit tricky. Photoshop likes to weight the channels for greyscale conversion, even layer palette to alpha palette, and that can cause some problems on occassion.

Also, if you are getting crazy with the layers, you might have to use ctrl + shift + c to copy merged.
 
I guess for colour the method I'm using is fine.

Good too know though, as it is clearly quicker for those occasions when B&W is the starting point of created images.

Thanks again

Sark
 
1...Can I paste a black & white image on to a layer mask to control the transparency/opacity of that layer. I know I can paint on a mask with black & white but I can't work out how to use an image as my layer mask.

This also works with a colour image as it is automatically turned to greyscale:
* copy the image you want to use as a mask with Ctrl+A (select all), then Ctrl+C (copy)
* add a layer mask to the layer you want to add a layer mask to
* Alt-click the icon of the layer mask in the layers palette
* press Ctrl+V to paste

2...Is it possible to make a selection of only what is visible through a layer mask.

Yes, just Ctrl-click on the layer mask icon

3...Is it possible to make a selection from a black & white (blurred) image layer so that the blurred (grey) pixels are selected as black pixels of varying transparency. Ultimately I want an alpha channel of the blurred black & white image, but as shades of black on a transparent backgr

shades of black *are* greyscale values. Transparancy does not really exist, it's in fact a simple trick: the more you let the pixels of the layer below influence the image, the more transparant it looks. PS can do this in 256 steps, and these can be made visual as greyscale values in a mask. Greyscale ranges from pure black to pure white with 254 greyscale values between then. Grey simply means (starting from RGB) that the three values for R,G and B are the same, ie: 128, 128, 128 which is medium grey.
 
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