Handling of 32 bpp images

[Jiri]

Why when showing preview in window of file opening IrfanView correctly detects 32 bpp PNG and BMP, but later in main window it shows 24 bpp in status bar?

And for 32 bpp PNG it at least lets choose menu Image - Show channel - Alpha, while for 32 bpp BMP the Alpha menu is greyed out as if alpha component did not exist?

[Bhikkhu Pesala]

IrfanView does not support full 32-bit transparency.

[j7n]

It's common for software to not recognize transparency in some formats. You sometimes have to juggle multiple editors. Photoshop considers transparency to be of a different kind in BMP and PNG although there is not a practical difference. One is read in as alpha and the other is baked into the pixel values. The use cases for 32-bit BMP are few. I think it only works Windows dialogs.

XnView works with 32-bit BMP.