GIF89A and PIL
in [Python]
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From: Stephen Hansen on 26 Mar 2010 21:45 Hi, all. Is it possible to get PIL to save GIF's in GIF89A format, instead of GIF87A? 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. Ahem. But the problem is, I have a nice, small little 72 byte GIF89A file, that I want to do some slight tweaking on and then re-save. I noticed that even if I completely skipped the tweaking step and -just- saved, it exploded into a 919 byte GIF87A file. And in this context, bytes really, really matter. I picked GIF over PNG because the same file in PNG was 120 bytes :) I'm not an expert on graphics, so I don't actually know for certain if its the fact that PIL is saving in GIF87A format that's causing the size to explode, it might just be that PIL is doing.. Something Weird when it saves it as a GIF, too. To demonstrate: >>> f = open('../tiles/BaseTemplate.gif', 'rb') >>> d1 = f.read() >>> len(d1) 73 >>> d1 'GIF89a\x10\x00\x10\x00\x80\x00\x00\xff\xff\xff\x00\x00\x00!\xf9\x04\x00\x00\x00\x00\x00,\x00\x00\x00\x00\x10\x00\x10\x00\x00\x02 \x8c\x8fi\xc0\xed\xbe\x9edq\xbej\x1b\xce`go\x81\x93(\x91W\xc0AhJ\xad\xac\xa9*\xb2Q\x00\x00;' >>> im = Image.open('../tiles/BaseTemplate.gif') >>> import cStringIO >>> cfp = cStringIO.StringIO() >>> im.save(cfp, format="gif") >>> cfp.seek(0) >>> d2 = cfp.read() >>> d2 'GIF87a\x10[...snip...]\x00;' >>> len(d2) 919 -- --S .... p.s: change the ".invalid" to ".com" in email address to reply privately.
From: Lawrence D'Oliveiro on 27 Mar 2010 00:37 In message <2010032618455468300-aptshansen(a)gmailinvalid>, Stephen Hansen wrote: > Is it possible to get PIL to save GIF's in GIF89A format, instead of > GIF87A? Why? What does GIF do for you that PNG doesn't?
From: Stephen Hansen on 27 Mar 2010 00:53 On 2010-03-26 21:37:10 -0700, Lawrence D'Oliveiro said: > In message <2010032618455468300-aptshansen(a)gmailinvalid>, Stephen Hansen > wrote: > >> Is it possible to get PIL to save GIF's in GIF89A format, instead of >> GIF87A? > > Why? What does GIF do for you that PNG doesn't? If I take this PSD and save it as a GIF as fully optimized as possible, its 72 bytes; do the same with PNG, and its 120. In this situation that difference really is very important. -- --S .... p.s: change the ".invalid" to ".com" in email address to reply privately.
From: Alain Ketterlin on 27 Mar 2010 11:17 Stephen Hansen <apt.shansen(a)gmail.invalid> writes: > Is it possible to get PIL to save GIF's in GIF89A format, instead of > GIF87A? GIF89 was patented. I guess that is why it isn't used by PIL. (The patent has expired now, IIRC.) Anyway, PNG was supposed to replace GIF. > 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. > But the problem is, I have a nice, small little 72 byte GIF89A file, > that I want to do some slight tweaking on and then re-save. I noticed > that even if I completely skipped the tweaking step and -just- saved, > it exploded into a 919 byte GIF87A file. And in this context, bytes > really, really matter. I picked GIF over PNG because the same file in > PNG was 120 bytes :) [...] >>>> f = open('../tiles/BaseTemplate.gif', 'rb') >>>> d1 = f.read() >>>> len(d1) > 73 >>>> d1 > 'GIF89a\x10\x00\x10\x00[...]' 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. (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.) 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. -- Alain.
From: Stephen Hansen on 27 Mar 2010 22:44
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. -- --S .... p.s: change the ".invalid" to ".com" in email address to reply privately. |