PNG alpha channel transparency Options

[Guest_Per Johansson_*]

PMView supports alpha channel transparency according to the help file, but I haven't been able to create such an image.
I have a big black and white 2-colour TIFF image that I make smaller, 10 %, and it becames a Truecolour grayscale image. I save it as a PNG image with transparency turned on, transparency colour 255, 255, 255. The white parts turn transparent when viewed in Mozilla or Opera, but the gray parts remain opaque.

How do a make an alpha channel transparent image?

[Per A Johansson]

PMView cannot save transparency masks. The only way to achieve transparency when saving is to use a transparent color.

What you're doing will work fine, however you need to invoke Color->Convert to Black&White before saving the file.

Auto-creation of a multi-level opacity mask is out of the scope of PMView. I recommend using the GIMP or Photoshop for this task. However, I doubt this will help. I'm sceptical to whether today's web browsers can use files with an alpha channel (opacity mask). Even if it works in one browser, I bet it won't work in all browsers (IE, Opera, Netscape, Mozilla...). My guess is that they will read the file without problem but they will not use the alpha channel data and the result is an image that is not transparent at all. Please correct me if I'm wrong...

I think it should be explained in the documentation that PMView cannot save transparency masks, or rather what you can and can't do with PMView.

Yes, I have now used GIMP to create the semi-transparent image. Current browsers can handle such images, except Internet Explorer for Windows, which may be considered a legacy browser these days, although you can't ignore it as long as it has most of the browser market.

Some sites returns different images for current and legacy browsers. Using that technique, semi-transparent PNG's can be used. For now, I'll stick with one-colour transparency.

There are demos here for those who are interested in how images are rendered (or ignored!) in different browsers:
http://www.libpng.org/pub/png/pngsuite.html