Thank you in advance,
Anatoly
PSD Format - how to read compressed...
Which version of the format are you talking about? For v6 (PackBits)
this code works. Does any documentation exist for versions beyond v6?
PSD Format - how to read compressed...
Documentation for versions beyond 6 does exist, but is not public. Version 6 however supports ZIP as well as packbits, the latter of course is significantly easier to implement. I know because I've written one.
Anatoly, are you sure photoshop uses exactly the same compression/decompression algorithm as ZLib? I wonder if Chris can confirm this. And what do you mean by ''the image is corrupt''?
''Not public''? That's non-existent as far as 3rd party developers are concerned. There was no sign of it in CS2, CS3 beta or ''Advanced'' CS2 SDKs.
I've never seen a PSD (even from CS2) that used anything other than PackBits.
Hi,
Thank you for your responses.
Toby, I saw your code, and RLE decompression works just perfectly, thanks a lot!
ZIP compression seems to be used in some 16bit files (though not in all of them).
I am not sure that Photoshop uses the same modification of ZIP as ZLib it was just an assumption. When I applied ZLib decompression, I got a correct size of the uncompressed data, and I was able to see the outlines of the images that had been compressed, but all the colors were messed up.
Does anybody know which implementation of ZIP I should use to decompress data from a .PSD file?
Toby, are you saying that ZIP compression has been dropped from CS? I don't have Photoshop CS, but I don't think that true. There is another PSD format/documentation that Adobe circulates but only to licensed/cleared/paid-up developers complete with NDA etc.
Anatoly, have you considered writing your own decompression module? I suspect that all the information you need to do so will be in the version 6 spec, else it wont be much of a spec. That said, I had to go outside the spec for detailed information on packbits compression. Else, try other libraries.
Unfortunately, the specification that I have (that one which came with Advanced SDK) doesn't say anything about ZIP - it just says that it is ZIP, and that's all. Probably I have to try to apply different ZIP implementations...
Nice idea. Do keep us informed about which implementation works.
Bear in mind zlib offers two different decompression/compression
methods, which use the same kind of compression but provide different
wrappers. You don't want the one used to make gzip files.
Aandi Inston
videohead, I've signed the NDA-like agreement for the ''Advanced'' SDK - and 9 months later I received some snippets of source code for Export and File Format plugins which merely confirmed things I'd already figured out.
No additional documentation for PSD/PSB was provided. It seems there is no ''kit'' as such, they just send material ad-hoc according to what they feel like passing on. My reply emails asking for further information have been ignored.
That said, I have no information about PSD's use of zlib/ZIP, and nor do I know how to get it, if it exists as you say. But that's not the only undocumented part of PSD, of course...
Is this same SDK you pay %26gt; $100 for, or the free one?
I've never seen them distinguished by Adobe, so I don't know what you mean. Is there some supa-sikrit SDK you only see if you're in the Partner programme? Which I now am...
videohead{at_char_here}mail.com wrote:
%26gt; Is this same SDK you pay %26gt; $100 for, or the free one?
Both the SKDs are free now. You just have to go through the website and request
them. I don't have the URLs handy.
-X
--
for photoshop scripting solutions of all sorts
contact: xbytor@gmail.com
Do you mean the Photoshop Format is now distributed free of charge? Does this SDK contain the photshop format info?
Neither the free CS2 SDK nor ''Advanced'' SDK - at least the bits I received - contain any information on file formats whatsoever. This is rather less useful than, for instance, the v6 SDK everyone received on CD.
As I said above, I don't know if there's an ''Really Really Advanced (We Were Just Kidding About That Other One)'' SDK that costs money that might have this info, and nor would I know how to get it, since Adobe personnel have not responded to any probing on such questions.
Naturally I welcome correction on these points by any whose jousts with Adobe have had better results.
I don't speak for Adobe, but I would guess that Adobe have decided
there is no commercial advantage in allowing third parties to read and
write PSD files, and have therefore stopped updating the
information...
Aandi Inston
The Advanced SDK just adds a couple of things. One of them is a pdf:
''Photoshop CS File Formats Specification.''
This does document the PSD file format along with other file formats (.atn,
.aco, etc...). I don't know how current the document is, but for the file
formats that I've been interested in (not PSD, BTW) it seems to be fairly accurate.
-X
--
for photoshop scripting solutions of all sorts
contact: xbytor@gmail.com
OK,
mea culpa, it's possible I just didn't request it. If I didn't, the reason is simple: I didn't want my related GPL work to be poisoned by the onerous agreement.
Toby_Thain@adobeforums.com wrote:
%26gt; OK, mea culpa, it's possible I just didn't request it. If I didn't, the reason is simple: I didn't want my related GPL work to be poisoned by the onerous agreement.
All of my work is LGPL. I don't recall there being any problem with any of the
agreements (e.g. no viral licenses like Microsoft's), but you should probably
read over it yourself or, better yet, have an attorney do it.
-X
--
for photoshop scripting solutions of all sorts
contact: xbytor@gmail.com
Of course I read it carefully myself (all 14 pages). And since I could not satisfy myself that it was safe to write GPL plugins under the terms of that agreement, I discussed it further with always-helpful Mark Niemann-Ross, who gave his verbal opinion (as he has
done on his blog) that it would not be a problem. But that discussion was more about the plugin API.
As you say, it's only prudent to get an attorney's opinion before taking the risk, when it comes to PSD docs. It seems safe to assume that Adobe is motivated to enthusiastically prosecute any leakage from controlled documents - as vaguely defined as such leakage may be - which must surely chill any GPL code that works with post-v6 PSD. But maybe I'm the only person on these forums who cares about the GPL (does anyone else actually write
GPL plugins?)
Toby_Thain@adobeforums.com wrote:
%26gt; But maybe I'm the only person on these forums who cares about the GPL (does anyone else actually write GPL plugins?
)
One thing you should consider, then, is talking with the authors of other Apps
that read PSD files and find out what they used for documentation. There may be
a body of reverse-engineered docs, if that's what you want.
-X
--
for photoshop scripting solutions of all sorts
contact: xbytor@gmail.com
Well, I'm happy with what I've done based on v6 PSD doc - it reads rasters from all subsequent versions, which is why (to get back to topic) I'm surprised if somebody found anything other than PackBits on rasters.
Toby, PSD supports ZIP as well, the docs say so. Have you tried reading a ZIP compressed image with your packbits-based program? Did it work?
No, it won't work (obviously) -
psdparse reads only uncompressed data and the single compression type defined in v6: PackBits (table 2-16). I cannot find a reference to ZIP in the File Formats document and I've never seen it in the wild, not even from CS2 - so how would one actually create one?? Perhaps the OP knows.
Here's a run on a CS2-created PSD; note compression type:
$ ./psdparse ~/Desktop/40843316_2534716d2d_o.psd -v
''/Users/toby/Desktop/40843316_2534716d2d_o.psd''
channels = 3, rows = 1024, cols = 768, depth = 8, mode = 3 (RGBColor)
(color mode data is empty)
Image resources (31334 bytes):
resource '8BIM' ( 1061,''''): 16 bytes
resource '8BIM' ( 1060,''''):16583 bytes
resource '8BIM' ( 1002,''''): 7600 bytes
resource '8BIM' ( 1001,''''): 120 bytes [Macintosh print record]
resource '8BIM' ( 1005,''''): 16 bytes [ResolutionInfo]
resource '8BIM' ( 1062,''''): 14 bytes
resource '8BIM' ( 1037,''''): 4 bytes [Global Angle]
resource '8BIM' ( 1049,''''): 4 bytes [Global Altitude]
resource '8BIM' ( 1011,''''): 9 bytes [Print flags]
resource '8BIM' ( 1034,''''): 1 bytes [Copyright flag]
resource '8BIM' (10000,''''): 10 bytes [Print flags info]
resource '8BIM' ( 1013,''''): 72 bytes [Color halftoning info]
resource '8BIM' ( 1016,''''): 112 bytes [Color transfer functions]
resource '8BIM' ( 1032,''''): 16 bytes [Grid and guides info]
resource '8BIM' ( 1054,''''): 4 bytes [URL List]
resource '8BIM' ( 1050,''''): 863 bytes [Slices]
resource '8BIM' ( 1064,''''): 12 bytes
resource '8BIM' ( 1041,''''): 1 bytes [ICC Untagged]
resource '8BIM' ( 1044,''''): 4 bytes [Document specific IDs]
resource '8BIM' ( 1036,''''): 4103 bytes [Thumbnail resource]
resource '8BIM' ( 1057,''''): 85 bytes [Version Info]
resource '8BIM' ( 1058,''''): 1094 bytes
resource '8BIM' ( 4000,''''): 268 bytes
resource '8BIM' ( 4001,''''): 28 bytes
(layer info section is empty)
(global layer mask info is empty)
merged channels:
%26gt;%26gt;%26gt; dochannel 0/3 filepos= 31380
compression = 1 (RLE)
uncompressed size 2359296 bytes (row bytes = 768)
channel 0 (@ 37526):
0: %26lt; 360%26gt; 05fafbfcfcfbfbf8fcfffdfdfcfffdf9fc08fdfcfdfefefdfd ...335 more
1: %26lt; 378%26gt; fffbfdfcfffd00fbfefc00fdfbfc01fbfcfdfdfffcf9fd00fe ...353 more
2: %26lt; 361%26gt; fffbfdfc07fdfcfcfdfcfcfdfdfafcfefd00fef7fdfefeffff ...336 more
...1018 rows not shown...
1021: %26lt; 728%26gt; 7b3437373b3c383c3c41464949484e525453544c4445224161 ...703 more
1022: %26lt; 727%26gt; ff3c5d3b3c342c2c26343b4144434b4d4f4d4a3c3b3d21535e ...702 more
1023: %26lt; 728%26gt; 0036fe37642d2a2e23252c3336333734362e2219293532645a ...703 more
channel 1 (@ 559903):
0: %26lt; 362%26gt; 05fafbfcfcfbfbf8fcfffdfdfcfffdf9fc08fdfcfdfefefdfd ...337 more
1: %26lt; 373%26gt; fffbfdfcfffd00fbfefc00fdfbfc01fbfcfdfdfffcf9fd00fe ...348 more
2: %26lt; 348%26gt; fffbfdfc07fdfcfcfdfcfcfdfdfafcfefd00fef7fdfefeffff ...323 more
...1018 rows not shown...
1021: %26lt; 723%26gt; 7f6b72777f828085888d92989a999fa1a1a2a39b97987394ba ...698 more
1022: %26lt; 731%26gt; 1e656b717876747874778088908f939292959084888c73abbe ...706 more
1023: %26lt; 734%26gt; 7f5f666d736f727a7168717a827f7f7979766861768484bcba ...709 more
channel 2 (@ 1086844):
0: %26lt; 379%26gt; 05fafbfcfcfbfbf8fcfffdfdfcfffdf9fc08fdfcfdfefefdfd ...354 more
1: %26lt; 388%26gt; fffbfdfcfffd00fbfefc00fdfbfc01fbfcfdfdfffcf9fd00fe ...363 more
2: %26lt; 362%26gt; fffbfdfc07fdfcfcfdfcfcfdfdfafcfefd00fef7fdfefeffff ...337 more
...1018 rows not shown...
1021: %26lt; 730%26gt; 5b707a818a8e8e94989da2a9abaab0b0b1b3b2aaa9aa84a4cc ...705 more
1022: %26lt; 728%26gt; 0c6b737b838280858187909aa09ffea26fa49c92989d81b9ce ...703 more
1023: %26lt; 729%26gt; 7f656e777e7b7e877e78818c928f8e898985746f869592caca ...704 more
done.
Try saving a document in Photoshop, and take a look at the compression options. You should find a ZIP option in there.
Re the ZIP in the file fomat/spec (version 6): take a look at pages 21, 24, 43.
I see now how the confusion has arisen. There is in fact no mention of ZIP
anywhere in Photoshop 6.0 File Formats Specification
Release 1 (September 2000). However, I just today stumbled across a copy of Release 2 - and you're right, it's right where you say it is. (I also stumbled across a copy of the Photoshop
CS File Formats document, which also mentions ZIP.)
But I cannot find an option to produce ZIP compressed PSDs in CS2 (I did say this above). Maybe it's intended for PSB.
You're right about Photoshop not having a ZIP compression option in its save dialog box (I use PS 7 and it too does not include such an option), however this is not to say that ZIP compression may not be employed behind the scenes. Search the help for ZIP and you will find the following bit of info:
''Photoshop PDF format supports all of the color modes and features that are supported in standard Photoshop format. Photoshop PDF also supports JPEG and ZIP compression, except for Bitmap-mode images, which use CCITT Group 4 compression.''
If you take another look at the 6.0 specs you will see that the ZIP compression option dates back to days of PS 3.0!
My guess is that PS somehow decides on a suitable compression option i.e. RAW (0), RLE(1), ZIP - prediction(2), ZIP + prediction(3). (Anatoly, have you tried both kinds of ZIP compression? Its not something you should have to guess. The ImageData::compression field should tell you the compression option that's been used.)
One last thing though, users are allowed to decide the image/layer compression type when saving multilayered TIFFs in PS. And as everyone knows ;-) , TIFFs saved in PS have a lot in common with PSDs. (Speaking of TIFFs, LibTIFF has some support for ZIP compression, and as everyone knows ;-) TIFF was originally developed by Adobe.)
PS:
Erm ... I thought the Photoshop CS File Formats document was not public domain!
It is very well known that TIFF, PDF, and PostScript since Level 2 support ZIP, etc. This has no relevance to PSD, of course. TIFF was NOT originally developed by Adobe (some of us can remember life before Adobe), but through acquisitions they are now its nominal ''owner''.
%26gt; you will see that the ZIP compression option dates back to days of PS 3.0!
I have no idea what you mean by that. It was not even mentioned until Release 2 of the V6 document, and even then, nobody is even sure if CS2 can generate ZIP compressed PSD. There is one very important reason why it would not arbitrarily choose compression types in the way you suggest: Doing so would unpredictably make files incompatible with older Photoshop versions (you may believe PS3.0 decompresses ZIP, but I don't for a moment).
As I said above, however, it is quite possible that PSB uses ZIP, even adaptively as you suggest. However the document does not even discuss whether this is true; discussion of ZIP is limited to about five words.
This is by no means ''documentation''; it's merely ''mentioning''. The File Formats document is one of the most incomplete and poorly expressed specs I've ever seen, as is soon discovered by anyone, like the original poster, or myself, who tries to use it to write working code. Some of the typos were fixed in the CS version, but none of the serious flaws and omissions.
Public domain? It's not my site. Anyone can find those links on Google.
Yes I did find the doc when I did Google search, and I was quite surprised that it was online because I thought version 6 was the last publicly available specification.
As for ZIP compression in version 3.0 of Photoshop, refer to pages 19-25 of the version 6 (rel. 2) specification. You will see that this specification mentions ZIP compression on pages 21 and 24.
I agree with you though that the specification appears far from complete. For example, I had to go search other sites for information on Adobe's implementation of a packbits (which really is a version of RLE).
Arguments aside, I wonder if Anatoly has tried to decompress the imagedata using ZLib with and without prediction.
%26gt; As for ZIP compression in version 3.0 of Photoshop
There is no such thing. Any inference otherwise from the
6.0 Release 2 documentation is incorrect.
If you can find a PSD with ZIP - if such a thing can be created at all - I'm more than happy to try to open it with 3.0 to prove this.
Once again, I suspect that ZIP is only relevant to PSB - although of course they omitted to explain.
Re: PackBits - Apple invented that particular RLE flavour. It was in the Mac Toolbox ROM circa 1984 and may have been used by the Lisa too. It's one of the TIFF standard compressors.
I've solved this problem, to uncompress the zip data. I'm the author of libpsd, you can download full source code from http://libpsd.graphest.com, and you can find it on sourceforge.net.
Cool! ... I only wish you'd posted this before I wrote my TIFF library.
Just a couple of questions though:
1. Is libpsd documented?
2. How exactly did you solve the ZIP uncompression issue?
Does anyone know how to create a ZIP compressed PSD/PSB in Photoshop?
After Photoshop CS, Adobe uses the zip format for data saving as default. If it couldn't work, set the color depth to 16 bit.
%26gt; After Photoshop CS, Adobe uses the zip format for data saving as default.
CS2 has only ever made PackBits PSDs for me, no matter what bit depth. Can you elucidate?
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