[kmike84]

A shameless plug: you can give https://github.com/kmike/psd-tools a try.

I've read PSD.rb docs and a bit of its code; the implementation is one of the best and complete I've seen (I've checked almost all PSD reader implementations some time ago).

But it seems that psd-tools is mostly on par with PSD.rb. It also have some features that PSD.rb doesn't have, e.g. full support for 'zip-with-prediction' compression, including 32bit layers. Such images are very common in practice, and parsing them is not easy because the compression format is not documented anywhere, and "zip-with-prediction" for 8 and 16bit layers is totally different from "zip-with-prediction" for 32bit layers (for 32bits it is really tricky).

If PSD.rb authors are reading this, I urge them to check the decompression code in psd-tools (https://github.com/kmike/psd-tools/blob/master/src/psd_tools...) or in Paint.NET PSD plugin (http://psdplugin.codeplex.com/) to not waste the time.

psd-tools also knows how to export individual layers, and there is an experimental support for exporting layer groups; it seems that this is not implemented in PSD.rb yet.

PSD.rb has some features that psd-tools doesn't have, e.g. it parses "Font data" which is really cool and hard because the format is not described anywhere.

[tluyben2]

I checked out psd-tools and it's good. Any chance of you adding their features to yours or vice versa? I know I know, I should do it myself and do a pull request, but just asking if you are planning to?

[kmike84]

Unfortunately I'm currently very busy with other projects, so I probably won't implement PSD.rb features myself anytime soon.

I'm trying to provide feedback for psd-tools pull requests, merge them and release new psd-tools versions in timely manner; the testing suite also helps here, so you know, pull requests are welcome :) Most improvements over last 6 months came from pull requests submitted by other great people.

I think that the "reader" part of library is feature-complete. psd-tools reads all the information, but it doesn't decode all Photoshop data structures (some of them are available only as binary blobs). So I think implementing a PSD.rb feature will most likely involve checking PSD.rb code and decoding a binary blob (already loaded to memory) to a Python data structure.

[tluyben2]

I didn't check your codebase (I just used the library for a few projects a while ago), so you don't have to answer. But if you want to enlighten others as well as me; am I right in thinking that you have a reader while reads the file and then have a 'decoding module' for every blob. So it would be rather straight forward to port from Ruby such a decoding part and plug it into your library?

[kmike84]

Yes, that was the idea.

The whole process is divided into 3 stages: reading, decoding and providing "user-facing API":

- on "reading" stage PSD file is read and split into binary blobs (I think this part is done);

- on "decoding" stage "decoding modules" are called for each binary blob; decoding modules should produce Python data structures that closely resembles internal PSD format;

- on "user API" stage decoded data is converted to more convenient format that is easier to work with (e.g. this include building layers hierarchy, and the PSDImage/Layer/etc classes).

I hope that providing new decoders will be rather straightforward, and it seems to work this way so far: contributors haven't touched "reader" part, and I haven't touched it for a while as well. But software development is hard, so we can never be sure :)

[kellysutton]

Nice! We should work together.

[kmike84]

Thanks!

Feel free to steal anything: test PSD files, etc.

If you want to implement layer blending in PSD.rb (required if you want to be able to export layer groups as images) then check libpsd C library - I think it has the most sophisticated open-source PSD blending implementation available.

Your PSD.rb and https://github.com/layervault/psd-enginedata libraries are very nice too; unfortunately I'm busy with other projects now, but maybe somebody will take effort and port PSD.rb features to psd-tools, or I could do this in future - the LayerVault's code will be very helpful.