alpha channel

Hi,

I've got a set of black and white images that I'd like to ad an alpha channel to to make it a black and alpha image - where the grey pixels are all actually black with a degree of alpha. The effect would be similar to using the screen effect on the layer allowing the layer below to show through the white completly and through the greys as if they were black pixels with a degree of alpha. I need this so that I can save out the images as transparent PNGs for use in Flash and other programs.

Can I do it with a plugin? or by a fancy select / alpha channel method?

Any help appreciated

Cheers
Guy

Can I do it with a plugin? or by a fancy select / alpha channel method?

Make a selection from the grayscale channel, invert it, and save the selection as an alpha channekl; or, in the Channels palette, drag the grayscale channel to the New Channel widgit, then invert the alpha channel that gets created.

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First, it sounds like you're confusing transparency (what it sounds like you want) with alpha channels (which don't have to be transparency).

But you can use transparency or alpha channels in Photoshop without any additional tools.

For PNG, you should just use transparency.

Consult your manual and online help for the topics of layers and transparency.

Chris

In article <408d0f77$0$24300$>, Guy Bowden
wrote:

Hi,

I've got a set of black and white images that I'd like to ad an alpha channel to to make it a black and alpha image - where the grey pixels are all actually black with a degree of alpha. The effect would be similar to using the screen effect on the layer allowing the layer below to show through the white completly and through the greys as if they were black pixels with a degree of alpha. I need this so that I can save out the images as transparent PNGs for use in Flash and other programs.
Can I do it with a plugin? or by a fancy select / alpha channel method?
Any help appreciated

Cheers
Guy

For an entertaining and accurate history of the alpha channel, check out Alvy Ray Smith's site:
http://alvyray.com/Memos/MemosMicrosoft.htm#AlphaHistory

--
Mike Russell
www.curvemeister.com
www.geigy.2y.net

Chris Cox wrote:

First, it sounds like you're confusing transparency (what it sounds like you want) with alpha channels (which don't have to be transparency).

But you can use transparency or alpha channels in Photoshop without any additional tools.

For PNG, you should just use transparency.

Consult your manual and online help for the topics of layers and transparency.

Chris

In article <408d0f77$0$24300$>, Guy Bowden
wrote:

Hi,

I've got a set of black and white images that I'd like to ad an alpha channel to to make it a black and alpha image - where the grey pixels are all actually black with a degree of alpha. The effect would be similar to using the screen effect on the layer allowing the layer below
to show through the white completly and through the greys as if they were black pixels with a degree of alpha. I need this so that I can save out the images as transparent PNGs for use in Flash and other programs.

Can I do it with a plugin? or by a fancy select / alpha channel method?

Any help appreciated

Cheers
Guy