View Full Version : Alpha problems

10.12.2007, 04:49 PM

I fond the following problems with IrfanView:

1) When I convert a 32 bit TGA to PNG, the alpha is lost. I was using the command line option /convert, then I tried opening IrfanView and "Save as". Why does it ask me to pick a color? The TGA already has an alpha channel, with alpha variations and not associated with any color.

2) Also cropping a PNG with alpha loses the alpha. Again I was using the command line option /crop.

3) I'm guessing the /panorama option also doesn't handle alpha. The only way I found to create a contact sheet in the command line is creating several panoramas.

And one suggestion: most programs, when displaying an image with transparency, use a checkered background behind it. It would be nice to have that in IrfanView.

11.12.2007, 12:36 AM
Yes, there is no alpha, that is why you have to choose the transparent color for the PNG. :(

I have to agree that a checkered background option for transparency would be nice, since it is hard to pick a background color that works with everything.

11.12.2007, 02:04 AM
No alpha indeed, so I have my doubts about calling this a bug-report.
I fully support++ the option to get a checkered background option for transparency.

13.12.2007, 08:41 PM
The PNG standard also defines an alpha channel so 24bit rgb + 8bit alpha TGA can in principle converted to 24bit rgb + 8bit alpha PNG. Currently IrfanView only supports a single color key. So support for 8bit alpha would be nice.