Comments on: Some thoughts about the PSD format

By: Mark

Mark — Wed, 27 Jan 2010 10:04:16 +0000

Actually, PSD originated in Photoshop 2.5 which did have both paths and duotones (those were introduced in Photoshop 2).
The primary ugliness in the PSD format stems from inconsistencies about how to handle lengths and padding and whether to use tagged values or fixed offsets for properties. There are other things that could be better, but those are probably the most glaringly “ugly” bits of the format. Over time, many of those conventions got sorted out — e.g., tagged values are better — but backwards compatibility meant that the old elements needed to continue to be represented the old way. What is sad is that PSB perpetuated this ugliness while creating a format the wasn’t going to be directly readable or writable by existing PSD readers.

By: Scott Ren

Scott Ren — Fri, 25 Sep 2009 23:57:50 +0000

Hi, I want to get “Adobe Photoshop file formats”, can you mail me a copy of it?
I want to know how .abr file format, and how it works.
Thanks.
e-mail:dsclub@vip.qq.com

By: Alexandre Jenny

Alexandre Jenny — Tue, 15 Sep 2009 08:12:42 +0000

Quote 1 : “John, I have seen many claims online that the PSD documentation was not complete, or up to date, and that total compatibility was not possible.”
I can confirm that. We have access to the latest documentation of the PSD format and it’s really far from up to date. 16bits mode layer not documented, 32bits not documented, etc. It’s a 2002 document. Please provide an update of that document.
Quote 2 : “What bugs me is why would anyone want to reverse engineer PSD file?” : Because Adobe Photoshop PSD format is a standard in the industry, so
as developer you have to be compatible with it.

By: Kamil Śliwak

Kamil Śliwak — Tue, 08 Sep 2009 08:12:58 +0000

I have worked on a PSD parser some time ago and the format itself is really not that bad. Yes, it’s inconsistent and suboptimal, but as this blog post says, it’s natural considering its long evolution and enormous amount of features it came to support.
Having said that, working with the format was real pain. Why?
1) Lack of freely and publicly available specs. And by free I mean available to anyone with no strings attached. Currently you have to sign an NDA and fax it to Adobe. It’s not an option for everyone. It’s good that it no longer requires ADN membership but the access to it is still too restricted.
2) The specs are incomplete and ambiguous. They only describe how the data is stored in the file and not how to interpret it. Data without interpretation is worthless. Most notable example: blending modes. The only thing provided in the specs is the name of each mode. Nothing about how it works and should be rendered, no formula. Yeah, it’s easy to figure out most of them but not all – I still don’t know what exotic variation of HSL/HSV color space is used by Hue/Saturation/Color modes. Or how to generate the exact pattern that dissolve uses.
More examples? Effect layers (glow, drop shadow, etc.). The file contains all necessary parameter values (blur, angle, intensity, distance) but their meaning is not always clear and it makes it impossible to recreate them faithfully.
I’d be happy if I could just forget about PSD and go with FXG but it’s not an option. PSD is used as de facto interchange format and software has to support it. It’s not possible without better documentation.

By: Phil Brown

Phil Brown — Mon, 24 Aug 2009 20:16:45 +0000

David – that looks very good (and your other codecs look interesting, too).

By: David Blake

David Blake — Mon, 24 Aug 2009 08:54:18 +0000

Coming soon to a 64 bit Windows PC near you. http://www.ardfry.com/psd-codec/

By: Abbey Sparrow

Abbey Sparrow — Mon, 08 Jun 2009 15:04:25 +0000

After not getting my mail answered, signing up for a useless 'developer account' and look for naught for some fax form that seems more than nebulous. Instead I recommend checking out: http://www.fileformat.info/format/psd/spec/index.htm where you can get what you need, when you need it (sure it's out dated, but it's better than jumping through hoops because the powers at be like to see people dance). I still wait with baited breath for a reply to my request on where the Fax can be requested, Mr. Nack.

By: Dan Gessel

Dan Gessel — Wed, 20 May 2009 11:15:15 +0000

The format structure is great for my purposes: raster image data in a standard form (PS CS4 wrote out a bunch of pngs), layer compositing info as simple metadata. But I don't see anything in the 1.0 spec that could represent, say, a levels adjustment layer. [I'm not sure what's spec'd, but I've heard discussions of how Pixel Bender could be used to express/re-create these adjustments. It may be that support for these don't show up for a while. --J.] I'm just squeakin' for some grease, man! [I'm certainly glad to hear your interest. --J.]

By: Dan Gessel

Dan Gessel — Wed, 20 May 2009 10:22:40 +0000

In the demo version of CS4 I just downloaded, adjustment layer info seems to be dropped.
A single file could just be a zip or tarball (underneath the hood), making it easy to pull apart with existing tools.
Is there a command line psd -> fxg tool?
[Unfortunately FXG support in CS4 is rudimentary at best. Please don't make any judgements about the quality of the format based on what you see now. We're making a much more concerted effort across the board going forward. --J.]

By: David Blake

David Blake — Fri, 15 May 2009 12:46:37 +0000

Had he sent the fax and received the documentation (as I have), he would have been disappointed. It does a fairly good job of defining the blocks layout in the file, but the precedence and contents of the blocks are sparsely documented.
As mentioned in this post, PSD was never meant to be an interchange format, but in the same post the you go to great lengths to point out how painful it would be if PSD went away. PSD _is_ a de facto interchange format. Adobe should acknowledge this and do a better job documenting it so that it can have better support.

By: YL

YL — Thu, 14 May 2009 08:01:49 +0000

“What other app lets you open & work with a file without having that file’s fonts installed?”
Microsoft Office. It allows users to embed fonts in their documents.

By: Alice Harris

Alice Harris — Wed, 13 May 2009 13:40:33 +0000

Adobe lighten up. This “anonymous developer’s rant about PSD” was not intended to be a widespread attack; it was a code comment. Programmers often relieve tension while coding by writing comments like that. It’s human nature to need to vent at times.
His point about the difficulty of obtaining the documentation is valid. You have to send a FAX to get it??? What decade is that policy left over from? And based on his comments (rather than on your extremely brief “summary” of his comments), it’s not just a fax saying “Please send the documentation to this address”, it’s a full-blown application form probably with some kind of signed legal statement and possibly with identification required. Of course people are going to baulk at that. If you want your format to be widely used, correctly used, and appreciated, make its documentation freely available on the web! (Both free as in beer and free as in no application required.) What possible harm could come to your company by publishing the documentation? Hiding it away behind an out-dated, convoluted application process just makes life unnecessarily harder for the people who use your format.

By: Alexey Danilchenko

Alexey Danilchenko — Mon, 11 May 2009 04:39:37 +0000

Although from user prospective the PSD is ok because it kind of works, I do tend to agree that as a developer – writing parsers and outputting something readable back to PSD is needlessly overcomplicated task.
Speaking of my personal experiences in this area, I wanted to implement a Lightroom filtering plugin (i.e. an export plugin that takes an image and transforms it somehow passing it further down the export pipeline). The problem here is that to correctly process all possible scenarios, I need to parse or at least to write the PSD file. The other suppported file formats (JPEG and TIFFs)are actually better in this respect as they are relatively easy to parse and write.
Now I am not complaining per-se but looking at what it will take me to do, and what time I would spend implementing just PSD parsing versus all other plugin work I need to do I decided to abandon all this because of the complexity ;-(
I guess my point here being that the curresnt situation whilst understandable, is sort of deterring the developers of other software to add support of PSD (at least for import/export kind of things) into their applications. And I am not sure whether it is actually a goal Adobe secretly pursuing by playing the funny games with the SDK/infomation access.
Regarding the documentation access, it is not that it is difficult to sign some pieces of paper and send it back to Adobe, it is really understanding why this is not open and available publically? What is Adobe afraid of by making it public and vailable updated with every released version of PS? SDK – I would understand as it has a code examples, but the file format docs? It also deters any development of opensource products that need PSD compatibility by using Adobe official PSD specs (as I believe a non disclosure is required to be signed off).

By: 墨尔本

墨尔本 — Sat, 09 May 2009 22:39:44 +0000

Nice post and great ideas.
Thanks so much for sharing

By: Keith Humm

Keith Humm — Thu, 07 May 2009 20:17:03 +0000

Ah, a ‘one true format’ – would be absolutely effing brilliant! Although I question whether XML is the best delivery mechanism; it’s hard enough to backup INDDs and PSDs let alone something twice their size!
I also hope FXG will allow some sort of state-based storage. It can’t be that hard – I don’t mind a file that’s 3-4x larger if I get to restore back 20-30 history points! Losing my Photoshop history after the damn thing crashes is possibly the most annoying thing I have to deal with on a daily basis!