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Brad Fitzpatrick

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HDR and Linux [Nov. 18th, 2006|08:24 pm]
Brad Fitzpatrick
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Anybody here do any HDR work with Linux?

I think I'm finally wrapping my head around all the concepts, formats, tools, processes, etc, but I've yet to do anything with any of it. Although I have some source images I'm eager to play with.

If my understanding is correct, there are basically two phases:

1) get multiple source images (on a tripod) of different exposures (shutter speed differences, not aperature) and run them through a tool to convert them into an HDR file (floating point pixel values, not 8-bit per channel). These file formats are either *.hdr or the ILM OpenEXR format? Or maybe some other formats. The tool mkhdr looks like it can do this, with some hand-holding. (you have to give it ppm files and shutter speeds on command line, since it can't read any raw files, but that's understandable because there's a dozen+ raw formats...)

2) given HDR file of some format (depending on tool), do cool shit with it. Canonical examples are various blurs that used to clip out highs, and "tone mapping", of which there are various algorithms it seems to reduce the HDR data down into something sexy for screen (which is low dynamic range)

So I guess my questions are:

-- best Linux tool for creating HDR images? is mkhdr good? I can automate the parameter hell.
-- best tools for converting between *.hdr and OpenEXR, etc? The imagemagick of HDR file formats?
-- best tone mapping algorithms to create the typical HDR photos you see online

Any pointers appreciated. Thanks!
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Comments:
[User Picture]From: deflatermouse
2006-11-19 09:59 am (UTC)

OpenEXR

I've done a lot of work with OpenEXR at previous $job so I can talk you through some of that stuff but, to be honest, we were using NothingReal Apple's Shake and/or custom tools to do most of our manipulation.

Fortunately, since Apple have decided to give up on Shake it's now dropped down in price to about $200. Unfortunately that's only for Macs. Unless things have changed the Linux version is still about $4000 per licence.

Also, Shake is unlike any Image Manipulation program you've ever come across - it's designed for compositing over a timeline and the interface is a DAG. You drop IO Nodes ((multiple) FileIn and (multiple) FileOut) into the script and then start dropping in other nodes (image mult, blur etc etc) in. Writing your own plugins is pretty easy and very powerful - they can either be a collection of collapsed nodes or written in C++.

Open Source wise there's a couple of GPL compositing tools that might help - Cinelerra (of which there are several different forks - it's a bit complicated) or the tool previous known as FilmGimp and no known as CinePaint.

If you want - I can talk you through some of that or, if what you want is some standard pipeline software, then code to read OpenEXRs is actually pretty easy and I can help you with that.

(Reply) (Thread)
[User Picture]From: iamom
2006-11-20 01:38 am (UTC)

Re: OpenEXR

Brad, I forwarded your post to a friend of mine who has a Ph.D. in CS with a specialty in imaging, and he also recommends OpenEXR for HDR rendering. As far as tone mapping operators are concerned, he says that there are many to choose from, that they're essentially task-dependent, but that the most common one is probably Ward's operator.

He said that one of the leading guys in this field is Paul Debevec, whose site is at http://debevec.org/.

Hope that helps a bit.
(Reply) (Parent) (Thread)
From: edge_walker
2006-11-19 05:24 pm (UTC)

Since I always want to recommend NetPBM, I googled [netpbm hdr], and that brought up multiple independent mentions of psftools. One of them is on the “Other HDR Software” page of WebHDR, which seems to be a web-based HDR compositor.

HTH.

(Reply) (Thread)
From: nathanmocks
2006-11-19 10:27 pm (UTC)
I'm not familiar with HDRs on Linux, but some pointers for Windows and Mac through my experiences:

-PhotoMatix is the best tool to create HDRs, if you happen to use PhotoShop, I have found that color are not as vivid
-for moving subjects, you can just shoot RAW, open it up in PhotoMatix, it will adjust the exposures, and create an HDR from just a single RAW, not as good as shooting three
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