Preserving existing alpha channels using irfanview PNG converter

Solution 1:

IrfanView is first and foremost an image viewing application, not an image editing application (although a number of helpful tools exist within the application). When it comes to saving the alpha channel, IrfanView is very limited. This is also explained in the IrfanView forum:

Irfanview is basically an image viewer. Alpha channel is just used to render against a background. then the alphachannel is gone. To keep the alpha channel means to use more memory and it must be handled in all image operations. This means a rewrite a lot of code.

Use different tools to preserve alpha channel during edit (like Paint.NET).

If you are primarily looking into PNG file compression I suggest you take a look at ImageOptim (if you are on a Mac), Trimage (Linux) or FileOptimizer (Windows, beware: it seems to be adware).

If you would like to use ImageMagick take a look at the alpha parameter. If I understand you correctly what you need is -alpha set.