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>That's the critical part. PNG is an archival format for me. Image formats come and go, but as long as the archive image's format is lossless it can always be c

>That's the critical part. PNG is an archival format for me. Image formats come and go, but as long as the archive image's format is lossless it can always be converted to another format without degradation if need be. Why not BMP then? Maybe I'm misunderstanding but I thought it was relatively free and relatively simple -- I thought you use things like PNG when you don't want a literal 1 for 1 (100% lossless) file. I thought if you use compression, you'll always lose at least a small amount of data. Or is that a fundamental misunderstanding? (If so, sorry to wander in like this, I'm not trying to sealion[1] you.) [1] wondermark.com/c/2014-09-19-1062sea.png

benhoyt 4y ago
> I thought if you use compression, you'll always lose at least a small amount of data. Or is that a fundamental misunderstanding? Yeah, that is a misunderstanding. There's lossless compression and lossy compression. For images, the classic example of lossless is PNG and lossy is JPEG -- with JPEG you get more and more artifacts/noise the higher your compression is, but with PNG you can always recreate the exact pixels of the original, hence the OP's use of it as an archival format. PNG is similar to how .zip and .tar.gz files work for executable files and other data -- those have to be lossless, because for text and executables and the like you need the exact 1s and 0s back out that you put in, otherwise the executable will crash or the text will be garbled.
- dontbenebby 4y ago
  >PNG is similar to how .zip and .tar.gz files work for executable files and other data Sounds like two things are being merged. (Like with tar.gz, tar is bundling the files together, gz is compressing them, versus an imaginary .targz which does both in one format.) Thanks for explaining, sorry I keep kind of... repeating things back at folks. It's how I'd speak verbally if trying to check my understanding, but it doesn't translate well to a comment thread. (I sincerely appreciate the clarification.)
  - benhoyt 4y ago
    You're not wrong, I should have just said .gz (though that really wasn't my point :-).
axiolite 4y ago
> I thought if you use compression, you'll always lose at least a small amount of data. No, the terms "lossless" and "lossy" are attached to different compression methods to indicate whether they do or don't discard data. Lossless compression methods like PNG, FLAC, ZIP, RAR, etc. will output the exact same input. Lossy compression methods, which discard some of the input data, include JPEG, MP3, AAC, MPEG-4 video (e.g. AVC, HEVC), and many more. As PNG is lossless, you can convert your BMPs into PNGs (which will make it far smaller) and back to BMPs, without a single pixel changing in any way. However, note that some PNG "optimizers" may introduce loss with some settings, like reducing the color space, but that's incidental to the format... You can reduce the resolution or color space of a BMP image to reduce its size as well.
- dontbenebby 4y ago
  >As PNG is lossless, you can convert your BMPs into PNGs (which will make it far smaller) and back to BMPs, without a single pixel changing in any way. However, note that some PNG "optimizers" may introduce loss with some settings Ok, TY, I think I grok it now. Yeah, if it's patent unencumbered and lossless, I'd rather see something like PNG used more than invent new file formats, though I respect the craftmanship that goes into some of the formats mentioned in this thread.

benhoyt 4y ago

> I thought if you use compression, you'll always lose at least a small amount of data. Or is that a fundamental misunderstanding? Yeah, that is a misunderstanding. There's lossless compression and lossy compression. For images, the classic example of lossless is PNG and lossy is JPEG -- with JPEG you get more and more artifacts/noise the higher your compression is, but with PNG you can always recreate the exact pixels of the original, hence the OP's use of it as an archival format. PNG is similar to how .zip and .tar.gz files work for executable files and other data -- those have to be lossless, because for text and executables and the like you need the exact 1s and 0s back out that you put in, otherwise the executable will crash or the text will be garbled.

dontbenebby 4y ago
>PNG is similar to how .zip and .tar.gz files work for executable files and other data Sounds like two things are being merged. (Like with tar.gz, tar is bundling the files together, gz is compressing them, versus an imaginary .targz which does both in one format.) Thanks for explaining, sorry I keep kind of... repeating things back at folks. It's how I'd speak verbally if trying to check my understanding, but it doesn't translate well to a comment thread. (I sincerely appreciate the clarification.)
- benhoyt 4y ago
  You're not wrong, I should have just said .gz (though that really wasn't my point :-).

axiolite 4y ago

> I thought if you use compression, you'll always lose at least a small amount of data. No, the terms "lossless" and "lossy" are attached to different compression methods to indicate whether they do or don't discard data. Lossless compression methods like PNG, FLAC, ZIP, RAR, etc. will output the exact same input. Lossy compression methods, which discard some of the input data, include JPEG, MP3, AAC, MPEG-4 video (e.g. AVC, HEVC), and many more. As PNG is lossless, you can convert your BMPs into PNGs (which will make it far smaller) and back to BMPs, without a single pixel changing in any way. However, note that some PNG "optimizers" may introduce loss with some settings, like reducing the color space, but that's incidental to the format... You can reduce the resolution or color space of a BMP image to reduce its size as well.

dontbenebby 4y ago
>As PNG is lossless, you can convert your BMPs into PNGs (which will make it far smaller) and back to BMPs, without a single pixel changing in any way. However, note that some PNG "optimizers" may introduce loss with some settings Ok, TY, I think I grok it now. Yeah, if it's patent unencumbered and lossless, I'd rather see something like PNG used more than invent new file formats, though I respect the craftmanship that goes into some of the formats mentioned in this thread.