How to tell if a Targa is from Photoshop?

Question

I have run into an issue while trying to write a *.tga file reader. For 32 bit targas, photoshop fills the alpha channel with 255, which is still standard, and works, but in 16 bit targas, photoshop fills the alpha bit with zeros.

Is there any way I can tell that a Targa has come from Photoshop so I can fill the alpha bit with 1s?

What if you check whether the alpha channel contains a 0 bit, and if it does, then set it to 1? — buc, Jan 15 '12 at 15:24
because that could break if someone loaded a 16bit image that was actually using the alpha channel — CuriousGeorge, Jan 15 '12 at 15:29
Well, he would rarely use the alpha channel to set _all_ pixels to zero alpha, would he? — ypnos, Jan 15 '12 at 15:34
There IS the case of the 1x1 transparent image, but other than that, this would work. — Mr Lister, Jan 15 '12 at 15:40

score 1 · Answer 1 · answered Jan 15 '12 at 15:38

1

The version 2.0 specification of the Targa file format contains a so called Extension area which has a Software ID field. This field holds the name of the application that created the file.

Maybe you could check whether Photoshop produces version 2.0 Targa files, and if it does what Software ID does it write to this specific field, then in your application check for this ID.

As Targa 1.0 file format does not have such a field, I'm not sure whether detecting Photoshop is possible at all.

answered Jan 15 '12 at 15:38

buc

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thanks, but there is no information stored after the image data =/ shouldn't photoshop be saving these images with a bit depth of 15 if they don't plan on using the alpha? – CuriousGeorge Jan 15 '12 at 15:57

How to tell if a Targa is from Photoshop?

1 Answers1