Select all transparent pixels in an image?

Question

Is there a way to select all transparent pixels in an image?

I have an image with lots of layers and lots of masks, and I want to select exactly the pixels that are 100% transparent in the image. (Or, alternatively, all the pixels that are not completely transparent).

I thought I could do this by creating a Fill Layer with a color that doesn't occur in the image, and then Select : Color Range… with a fuzziness of 0 and clicking on one of the colored pixels. But it turns out that this only partially selects the transparent pixels, unless the Fill Layer is Black or White. (Try it out, I was surprised by this behavior). There is also the problem that if you accidentally choose a color in the Fill Layer that happens to be in your image, you will perforce select those pixels too.

I have a way to do this that is a little convoluted, but I thought that there might be a one-step solution.

TIA

Semaphoric · Accepted Answer

Wasn't at the computer before, so I couldn't check, but this seems to work (you can make a Action of it):

With all layers visible, Stamp Visible (Control+Alt+Shift+E)
Select Transparency of the stamped layer
Enter Quick Mask
Invert
Threshold = 255
Exit Quick Mask
[Optional] Delete the new layer.

You could change the location of the Invert step, but you may have to change to Invert Selection and/or Threshold = 1.

Semaphoric · Answer

Load the layer transparency as a selection. Enter Quick Mask mode. Image > Adjustments > Threshold [set to zero]. Exit Quick Mask.

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