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Comment by basseq | Hacker News Reader

I enjoyed the writing and exploration of different image creation formats. So novice question, but are the resulting GIFs actually different (and if so, how)? Or is this just different ways to generate identical output?

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I saved the whole page in order to grab the images all at once, then used md5sum:

    [images_files] 0 $ md5sum * | sort
    4a93faba1d6abc2f3c0fa4a925a23a4c  viii.gif
    672b8ee4b7e2893f209dd66eeb368744  ix.gif
    7005d06133499ca4d1e6d1b265adea83  ii.gif
    784f2d5bc7cb0cdce826fb656896c034  v.gif
    8e39d526b119fabfacb259d53eb89140  vi.gif
    9d2e88d7588d5e22c9d51d6b005034fb  vii.gif
    9f55b70b1564ab62faafbf37f311c5c0  iv.png
    b67f99e04dc8720d5846b818e86ecd39  style.css
    eb42e0f64ece46753a7aeba4fe3149a6  i.png
    f346c6fbe6fa659b6020c75c579084de  iii.gif

So I'd say no, they're different for some reason. Sizes vary a lot, too. Unfortunately I don't even know where to begin telling why.

they probably have different metadata. if you convert all of them to png, do they still differ?

There are already 2 pngs in that list, and they already have different md5s

that could be caused by different compression levels or other artifacts in the metadata.

my expectation was that in the conversion, metadata and possible artifacts that stem from different tools used to create the image would be normalized.

in the sister reply diggernet choose even better formats than png as conversion targets, and answers the original question in this subthread

Interestingly, if they are all* converted to ppm, only iii and ix are the same. Only part of the difference is comments. There are also differences in value encodings.

Also, if converted to bmp, only ii and vi are the same.

Edit: Converted to xpm, all are different. (When the embedded filenames are reconciled, ii and vi are again the same, the rest differ.)

*Except v.gif, which is invalid.

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