omg 1 by timcaynes

my trivial task is to produce a high dynamic range image from a single camera raw file and tone map it or suchlike to see just how ridiculous I can make a car park look even though there might be multiple places I could post it and probably get a number of sword of damocles awards for outstanding friggery. simple enough. except I, not unreasonably, want to use the tools I already have notably a camera a computer and adobe cs3. that's ok, because adobe cs3 includes the merge to hdr script for mashing up multiple source files with different exposure bias values and so all you have to do is make a bunch of source files with different exposure bias values and spong them through the software mincer in photoshop and lo, a metallic tone-apocalypse vision of hell effect.

but photoshop is cleverer than you. its read all the flickr groups and forums about hdr and it knows that hdr requires multiply-bracketed source files straight from the rawness of your tool. don't try and be doing that single raw exposure adjustment, that's not right. it needs to be fed multiple files. but that's alright, you just open your raw file up in camera raw, adjust the exposure and save it out to 16-bit tiff files. viola, multiple source files with different exposure bias values. but no, because photoshop is cleverer than you. it knows you did that because the metadata says so. huh? what metadata? I'm looking at that metadata right now, thankyou, and the exposure bias says, oh, it says 0. on all of them.

so then, I'll just edit the EXIF values myself then and see how you like that. 5 EXIF editors later and I finally find one that actually allows you to edit the exposure bias value in the EXIF data and so here we go, that one's +1. that one's -2. that one's -3. ooh, that one's 0.5. right, save. now, take that, photoshop, and eat my exposure cake.

what do you mean they're all exposure bias 0? dammit! I just changed all those value by hand. rummage rummage forum google forum. oh, I see. its like that. you don't read THAT data, you read THAT data. so why'd you have to go and use XMP for that stuff? 5 editors later and I don't find one that allows me to edit the XMP data or any documentation on converting the decimal EV values to the text XMP values (wtf is the xmp:ExposureBiasValue/xmp:ExposureBiasValue equivalent of -3 anyway?) so I begin to think that even using photomatix is an option. but there is one last nasty throw of the dice left. if you don't mind throwing ALL your metadata away and starting from scratch, then you're in business. all you have to do is take the exposure adjusted tiff files you started with, copy the pixels in new documents and save them, preferably with some stupid filename indicating the ev values. then, when you load then in the merge to hdr script in photoshop it tries to work out just what the exposure bias values might be and suggests things like 9.7 when its actually -1, but it gives you the option the enter them manually before it goes off and does its whole 32-bit hdr jiggery-pokery.

of course, it turns out that the results of doing this are the same as the results you first thought of when you simply fed it your multiple ev adjusted tiff files and it told you that they are actually all ev 0. it looks to me like the merge to hdr doesn't really do much other than make the conversion to 32-bit and then stamp on it with a great big software boot. its the 16-bit conversion where everything happens and so it doesn't really matter how you get to that point. tell me that's not true, but I couldn't tell the difference. the same effect is probably achieved by taking the singe raw, saving as tiff, converting to 32-bit and then converting back to 16-bit, although the dynamic range might be limited but then you only copied that 1 file in the first place and its all the same data so why waste your time. you're not doing hdr at all, you're just tone mapping. get over it.

© Tim Caynes. This work is licensed under a Creative Commons License

Disclaimer: I work for Sun Microsystems, but this is nothing to do with them and it's all my fault, even though I might sometimes mention Solaris or something.