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pngout: img w/alpha unsupported format
- This image uses alpha. I believe it has a 32 bit alpha channel:
http://members.cox.net/valenzdu/Think48.png
When I try to compress this image another other's like it, pngout give me the following message.Think48.png unsupported format
- PNGOUT does not support 16-bit color components. You'll need to convert your image to an 8-bit format in some other program before you can use PNGOUT with it. Sorry.
- Sorry, for the confusing message. Yes, all channels are 16 bit. (What was I talking about? :oops: )
I'm just curious, why are 16bit channels more difficult to work with than 8 bit channels? Wouldn't the IDAT compression code be the same? - Images with 16-bit color depth are not more difficult to work with. The problem is I have designed my libraries to use a 32-bit "ARGB" pixel format internally and I have many applications that depend on this particular structure. Until I see the benefit of images that have 16-bit color depth, I am unlikely to change this.
- If you want to compress it further as a 16-bit image, you might have better luck with OptiPNG and AdvDef; they should work with any type of PNG. I suggest using them in that order.
Ken, I just thought I'd ask: would it be hard to add an indiscriminate "recompress only" option to PNGOut? Then it would be possible to use your deflate code on PNGs that PNGOut can't make, like 16-bit or interlaced PNGs. - A "recompress only" feature would be easier to hack into KZIP than to PNGOUT. Actually, all you really need is a utility that could exchange the PNG header with a ZIP header (and vice versa). I'm not saying that's an easy thing to do, but at least it spares you from having to learn the technical details of the deflate algorithm.