Grayscale Image -> Alpha Transparency?

MN
Posted By
Mitch_Nelson
May 12, 2007
Views
707
Replies
4
Status
Closed
– I have a white logo on a black background. It has anti-aliased edges.

– I want to turn it into a white logo on a transparent background, where the anti-aliasing will be semi-transparent.

– This way, I can put my white logo on any background I want and have smooth edges that blend seamlessly into the background.

– (So, for example, the original 25% brightness at 100% opacity would become 100% brightness (white) at 25% opacity.)

– How do I do this?
Related Tags
alpha grayscale image transparency

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EH
Ed_Hannigan
May 12, 2007
Make Background a Layer. Invert so it’s a black logo on a white background. Make a new layer below and fill with a color as reference. On the logo layer double-click to get the Layer Style dilaog and in that dialog pull the rightmost bottom sliders left until all the white has turned transparent.

Now you have a black antialiased logo on transparent background. Select All, Copy. Make a new layer, fill with white. Make a blank Layer mask on it. Alt-click to reveal the Layer Mask and Ctrl-V to paste into it and Ctrl-I to invert the mask.

Trash the logo layer. Pull the mask to the trash and click Apply. Now you have an antialiased white logo on a transparent background.
EH
Ed_Hannigan
May 12, 2007
Invert the layer so you have a black logo on a white background. Go to the Channels Palette, Ctrl-click on the Composite channel (RGB or CMK) to make a selection. Back on the Layers palette, click on the Layer Mask icon to make a mask of the selection, then click on the original layer, select all and fill with white.

Pull the mask to the trash and click Apply.
MN
Mitch_Nelson
May 12, 2007
I seem to have found an even simpler way. Black logo on white background, ctrl-click on the composite channel, press delete. Is there anything wrong with this method?
EH
Ed_Hannigan
May 12, 2007
Nothing wrong with that.

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