GIF89A and PIL
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From: Harishankar on 27 Mar 2010 23:32 On Sat, 27 Mar 2010 19:44:54 -0700, Stephen Hansen wrote: > On 2010-03-27 08:17:46 -0700, Alain Ketterlin said: > >> Stephen Hansen <apt.shansen(a)gmail.invalid> writes: > >>> If not, are there any decent other image libraries out there that >>> anyone's familiar with? The only one I could find was PythonMagick, >>> which seems completely undocumented. Or I'm blind. >> >> I don't know PythonMagick, but it is based on ImageMagick, which is >> kind of a swiss-knife in image manipulation and conversion. You could >> try the standalone tools first, to see if you get what you want/need. > > Well, I know it -can- do what I need, except the subprocess business > isn't something I want to deal with. And the library seems utterly > undocumented. :( > >> Hmm, a 16x16 image. Don't expect much from the most sophisticated >> formats (e.g, PNG), because their overhead (headers etc.) may well be >> above the size of the data. Compression isn't usually targeted at small >> files. > > Yeah, I don't expect much from PNG. The images are very small but I > might be sending a LOT of them over a pipe which is fairly tight, so > 50-60 bytes matters. That's why I selected GIF. > >> (BTW: "slight tweaking" may have an effect on file-size if it >> introduces new colors, because GIF uses a color-table. I guess you know >> all this.) > > Yeah, I know this is possible, which is why the tweaking was to be very > careful: these images all have only a couple indexed colors each, and I > should be able to do the tweaks and not increase the size excessively. > > However, the problem is: I left out all the tweaks and it still exploded > in size. > > Just opening, and then saving the same file with no changes at all, > resulted in a 72 byte file growing to 920. > > I thought it was GIF87a vs GIF89a... but have since come to determine it > doesn't appear to be. I decided to give PNG a try again, since those > extra 50 bytes *matter*, but if I can't get GIF to work, 50 is better > then 900. Unfortunately, I hit the same wall there. > > If I convert these itty-bitty images into PNG, they're about 120 bytes > or so. Opening one in PNG, making no changes, and saving, results in the > new file being 900 bytes too :( > > So I wonder if there's just some hyper-optimization Photoshop does that > PIL can't round-trip. > >> GIF uses the LZW algorithm, and so does zip and gzip (the latter with >> an additional layer of Huffmann coding). If your images are of fixed >> size, you _may_ be better off compressing the raw data with a general >> purpose compressor (i.e., gzip). Check the packages gzip and zlib. > > Hm. I hadn't thought of compressing the saved version. I could do that, > I suppose: it just seems there is so much extra stuff which shouldn't be > needed that's being saved out. This might not be of much use to you, but I've found by experience that PNGs are almost always bigger or equal to GIFs of the same resolution, colour depth and so on. I've never yet seen a PNG file that is smaller than a GIF for the same set of pixels. As mentioned above, compressing raw data stream might be more beneficial in this situation. Also try the pngcrush utility and see what size it gives you. http://pmt.sourceforge.net/pngcrush/ -- Harishankar (http://harishankar.org http://literaryforums.org)
From: garabik-news-2005-05 on 28 Mar 2010 03:22 Harishankar <v.harishankar(a)gmail.com> wrote: > >> Just opening, and then saving the same file with no changes at all, >> resulted in a 72 byte file growing to 920. >> >> I thought it was GIF87a vs GIF89a... but have since come to determine it >> doesn't appear to be. I decided to give PNG a try again, since those >> extra 50 bytes *matter*, but if I can't get GIF to work, 50 is better >> then 900. Unfortunately, I hit the same wall there. >> > Also try the pngcrush utility and see what size it gives you. > http://pmt.sourceforge.net/pngcrush/ > optipng gives slightly better results. Anyway, depending on your pictures, you might find out that using *.ppm.gz, *.pgm.gz or *.pbm.gz outperforms both optimised gif ad png... and if sending more pictures down the line, tar-ing them (*.p?m) and compressing the result will give even better sizes. -- ----------------------------------------------------------- | Radovan Garabík http://kassiopeia.juls.savba.sk/~garabik/ | | __..--^^^--..__ garabik @ kassiopeia.juls.savba.sk | ----------------------------------------------------------- Antivirus alert: file .signature infected by signature virus. Hi! I'm a signature virus! Copy me into your signature file to help me spread!
From: Gregory Ewing on 29 Mar 2010 03:41 Stephen Hansen wrote: > So I wonder if there's just some hyper-optimization Photoshop does that > PIL can't round-trip. You may find that PIL isn't bothering to compress at all, or only doing it in a very simpleminded way. -- Greg
From: Gabriel Genellina on 30 Mar 2010 00:00 En Mon, 29 Mar 2010 04:41:23 -0300, Gregory Ewing <greg.ewing(a)canterbury.ac.nz> escribi�: > Stephen Hansen wrote: > >> So I wonder if there's just some hyper-optimization Photoshop does that >> PIL can't round-trip. > > You may find that PIL isn't bothering to compress at all, > or only doing it in a very simpleminded way. Indeed. Fredrik Lundh, in http://mail.python.org/pipermail/image-sig/1998-July/000506.html "When writing GIF files, PIL uses a simpleminded encoding that, by some odd reason, LZW decoders have no trouble reading. To write compressed GIF files, there are a number of options: -- install NETPBM, and hack GifImagePlugin so it uses _save_ppm instead of _save (just remove "_ppm" from the latter). -- write an _imaging_gif module that takes a PIL image and writes a GIF version of it. how you implement that is up to you..." After twelve years the above comments are still applicable. -- Gabriel Genellina
From: Cameron Simpson on 30 Mar 2010 00:41
On 27Mar2010 19:44, Stephen Hansen <apt.shansen(a)gmail.invalid> wrote: | Yeah, I don't expect much from PNG. The images are very small but I | might be sending a LOT of them over a pipe which is fairly tight, so | 50-60 bytes matters. That's why I selected GIF. How well does a stream of XPM files compress? Probably not enough, I would guess. Just wondering. Do you need to move a "standard" image format around? If everything's 16x16 8 bit colour (and if, with luck, they share a colour map) maybe you can ship raw bytes expressing what you want. How colourful are these GIFs? -- Cameron Simpson <cs(a)zip.com.au> DoD#743 http://www.cskk.ezoshosting.com/cs/ What I want is Facts. Teach these boys and girls nothing but Facts. Facts alone are wanted in life. Plant nothing else, and root out everything else. - Charles Dickens John Huffam 1812-1870 Hard Times [1854] |