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by doubloon 923 days ago
ok thats pretty wild, you would take the zlib deflate/inflate code, (for example in a library like lodepng) and then like chunk 95% of it in the garbage? so basically every block would just be uncompressed? kind of funny but it would probably work pretty well and your code size could get down way way smaller than the current typical png code.

seems like the downside is that this is "worse than nothing" compression, the image file would be bigger than the original blit of the data. for example 1024x1024x32bit color means 3 megabytes for one image. or do i miss something?
2 comments
RaisingSpear 923 days ago
Many PNG compressors allow you to specify the zlib compression level, where 0 = no compression. This will effectively give you an uncompressed image, perhaps with some format overhead.

Your math is a bit off - a 1024x1024 at 32bpp would be 4MB, ignoring overhead.

I've actually done something like this in the past - create PNGs with 0 compression, then compress it with something stronger than Deflate (like LZMA). Because the PNG filtering is still applied, this allows greater compression relative to PNG by itself (or a BMP compressed with LZMA).

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doubloon 916 days ago
right but the "compression/decompression" code essentially becomes, like what, 10 lines of C? down from several thousand
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RaisingSpear 916 days ago
Certainly, if your aim is the simplest code with no regard to compression, you could achieve a PNG writer with a small amount of code.

In such a case, you could also skip the PNG filtering as well (whilst for my case, you wouldn't want to).

I think it'd make more sense to go with BMP for a 'simple as possible' image format, that has wide support, than with PNG. PNG is definitely more geared towards a compressed image (as well as all sorts of other features you may not care about).

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Retr0id 923 days ago
There's no need to take anyone else's code, emitting uncompressed DEFLATE blocks is trivial. I'm not sure what you mean by garbage?

> for example 1024x1024x32bit color means 3 megabytes for one image.

You do miss something, that's 4 megabytes, plus any header/format overhead - but you'd get similar performance out of any uncompressed format, that's just the tradeoff.

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doubloon 916 days ago
i mean the PNG code, youd have to have some PNG code in addition to the DEFLATE code yes?
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