Layer Mask or Alpha?

DJ
Posted By
dennis johnson
Sep 16, 2003
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530
Replies
4
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Closed
When I add a Layer Mask to an image (PS 7.01), the Channels Palette shows what appears to be an alpha channel added to the image.
Yet if I save the image as TIF, then open the image in Shake or Gimp, the image opens as RGB, not RGBA. No alpha channel or alpha transparency is seen by the other apps.

If however, I take the same image in Photoshop, go to the Channels Palette, duplicate the Layer Mask-created "alpha" channel, naming it "alpha" – so that I now show TWO "alpha" channels in the Channels Palette, I can then open it in Shake or Gimp and it will appear as an RGBA image with alpha transparency.

So – was the original extra channel generated in my image by adding a Layer Mask an alpha channel, or not? And if it wasn’t an alpha channel, what was it? (Also, if it wasn’t an alpha channel, why when I duplicated the thing did I then have an alpha?)

So far as I can tell, the Layer Mask tool only produces transparency WITHIN Photoshop. Are there any other apps that recognize images with a Layer Mask applied as having alpha transparency or even an alpha channel?

This has been a frustrating day…
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Y
YrbkMgr
Sep 16, 2003
Dennis,

My understanding is this:

A layer mask is NOT an alpha channel and a layer mask may or may not be respected across apps (say for example Paint Shop Pro, or Illustrator).

When you create a layer mask, the Channels Palette shows an off color, slightly lightened temporary channel and ONLY when you click on the layer with the mask (which I find convenient to duplicate in the Channels Palette). But when you click on a layer without the mask, the temporary channel does not display.

When you duplicated the mask, you created a permanent alpha channel that is saved, as an alpha channel, according to whatever specifications the file format requires (PSD, TIFF, Targa, etc.)

Look at the Channels Palette when you use the QuickMask tool for selecing something in the image. It also creates this temporary indicator that a mask is present.

So in sum, masks are not alpha channels, but can be manipulated as such while in photoshop, but one should not expect them to be universally preserved across file types and applications.

That’s my two cents anyhow…

Peace,
Tony
L
LenHewitt
Sep 16, 2003
Dennis,

There are very few applications that recognize TIFFs saved with advanced options correctly. In fact, Illustrator 10 is the only application other than Photoshop that I am aware of, although InDesign 2 may well also support them
DJ
dennis johnson
Sep 16, 2003
Thanks for your input, gentlemen. The problem would have been clearer if I had been working on an image with multiple layers – I would have seen that the Layer Mask "alpha channel" only showed up on the layer the mask was created on. (Hence the name "Layer Mask. Altogether now…"duh"!)

🙂
P
Phosphor
Sep 17, 2003
Dennis,

My theory is, that we must all have, "duh, slapping of the forehead moments" to be able to truly appreciate the success of the moments when we are blessed with PS divine knowledge!

Personally, I can’t wait for a little less bruising of the forehead and more "divine" moments!

How much longer do you think???

Patty 🙂

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