Edit PNG transparency

[Ivo]

Hi, everybody.

As part of tweaking my Win7 theme I want to edit the transparency of some PNG images. If I open the PNG file in Photoshop it gets converted to a layer and the transparency is implicit instead of explicit like a separate Alpha channel. I could not find a way to edit that transparency directly. Talking to a few artists I got the following suggestions:

- tweak the layer transparency with the slider. The problem is it is already at 100% and I can only make things more transparent but not more opaque

- duplicate the layer to make it less transparent. This only lets me change the transparency in big steps

- Ctrl+click on the layer and convert the selection mask to a layer mask. The problem is that Photoshop messes up the values. Value of 50 becomes 69, value of 100 becomes 123 and 200 becomes 212. Like some sort of gamma correction. Very bad.

I'm really surprised there is no direct way in Photoshop to edit the per-pixel transparency of a PNG file. I want to be able to see it as an 8-bit grayscale image and paint on it, apply filters, etc. just like I can manipulate an Alpha channel.

What are you guys using to solve this problem?

 

[Mark]

Hi, everybody.

As part of tweaking my Win7 theme I want to edit the transparency of some PNG images. If I open the PNG file in Photoshop it gets converted to a layer and the transparency is implicit instead of explicit like a separate Alpha channel. I could not find a way to edit that transparency directly. Talking to a few artists I got the following suggestions:

- tweak the layer transparency with the slider. The problem is it is already at 100% and I can only make things more transparent but not more opaque

- duplicate the layer to make it less transparent. This only lets me change the transparency in big steps

- Ctrl+click on the layer and convert the selection mask to a layer mask. The problem is that Photoshop messes up the values. Value of 50 becomes 69, value of 100 becomes 123 and 200 becomes 212. Like some sort of gamma correction. Very bad.

I'm really surprised there is no direct way in Photoshop to edit the per-pixel transparency of a PNG file. I want to be able to see it as an 8-bit grayscale image and paint on it, apply filters, etc. just like I can manipulate an Alpha channel.

What are you guys using to solve this problem?

I will usually duplicate the image and then make the top layer more transparent with the slider then merge the layer down if you want to or just save it as a png

 

[MattRainier]

Get GIMP!

Simple - duplicate the layer (probably multiple times), then adjust the opacity of each layer individually until you get the desired effect.

I think that's what Mr GRiM was trying to get at, but I'm not sure.

 

[Ivo]

But I am a programmer! I need exact values and per-pixel accuracy!!!!

Does GIMP offer editing of the PNG transparency as a grayscale image?

 

[FinEd]

With Paint Shop Pro 8 and later you can edit the alpha channel on png images. Just go to File Format Preferences -> PNG tab -> select "Load and save transparency to / from alpha channel".