Sunday, January 16, 2005

Getting Back Into Things...Custom Color Profiles

Wow, long time since my last update. Really didn't mean for this to happen. Time to sum up what's been going on.

Since my last post in December, I spent some time working with Wayne from my photography class (which has now ended). He picked up a GretagMacbeth Color Chart, and we did some work with Adobe Photoshop setting up some custom RAW conversion profiles. Normally I do all of my RAW conversion with C1, which doesn't give you the option of setting up custom profiles (or at least the LE version doesn't...not sure about pro), but it does have some built in profiles, including one for the Digital Rebel. I really couldn't imagine having to go back to Photoshop's RAW workflow (very primitive and clunky compared to C1). However, my goal was to learn how custom profiles work, learn how to create them, and then decide if the difference was significant enough to consider using Photoshop for RAW conversion, either full time or (more likely) just to process my most important images.

The first step is to lay out your color chart, get it very evenly lit, and then take your shot. You want to get the chart as straight on as possible (without shadowing it) and to get it exposed as hot as possible (without blowing it out). After you do this, you then load the image in Photoshop's RAW converter, set the exposure, set white balance, then adjust brightness contrast and shadow, and finally the saturation. The goal in the above adjustments is to get certain patches on your exposure of the color chart as close as possible to the reference numbers on the source color chart. Finally, you go through the settings on the calibrate tab, adjusting them all repeatedly until everything is as close as possible. Its a real pain to do it, but when you are done, you should end up with a reasonable close match.

Well, our first time through it, for the life of us, we just couldn't get anything to match up very well. We went strictly by the numbers, and when we finally got things not perfect, but as good as they wanted to get, our colors were horribly wrong. We spent a couple hours working on this without success before finally calling it quits for the day. My hope was that I'd be able to go home and work on my own a little more freely and be able to figure out what went wrong.

Well, it didn't take me long at all to figure out what happened. The reference chart we were using was designed in the PhotoPro RGB color space, and the (R,G,B) values printed on it were the values in that color space. However, the images we were working with were in AdobeRGB color space, and we were trying to get the (R,G,B) values in AdobeRGB to match the (R,G,B) values for PhotoPro. A recipe for failure.

So, feeling stupid enough, I got back on track, created color charts for working in AdobeRGB and sRGB space, and was able to hammer out a reasonable configuration. However, it was a real pain and very nerve racking since you can never get it perfect and changing a setting to make one color a better match ends up making another color a worse match. My next attempt was to download the ACR-Calibrator script written by Thomas Fors. It goes through the process of RAW conversion iteratively changing each parameter a little at a time until it finds the best set of parameters. Seems like a quick and easy script to run. Well, it's certainly easy, but not quick. The process took over 2 hours on my AMD 2800+, as it took nearly 900 RAW conversion to come to a solution. And the results were quite promising, matching much better than my by hand configuration did.

So, how did it end up? Well, the grayscale patches on the chart matched up very well, but the colors were hit an miss. Some were nearly indistinguishable from the source chart, but other were way off. So after all of this, the real question was, how did it hold up to C1? Well, it was a very mixed result. First off, it feels like a really unfair comparison since Photoshop gives you all these option to adjust it precisely, and with C1 you really just have to eyeball things and make a few slight tweaks. However, you have to remember that comparing what kind of results you get with the options available to you is what this whole test was about. So with any unfairness safely out of mind, here is what I felt after coming up with my best approximation in C1.

The grayscale patches were definitely closer in Photoshop, but the color patches were a toss up. Overall, I think Photoshop did a better job matching the brightness of the colors. C1 tended to give brighter results on many, but reducing the brightness in C1 to make those colors match would just make others darker. I don't doubt that with enough tweaking (contrast, curves, etc) I could get C1 looking better (and this would probably give better results for the grayscale patches too). On the other hand, when it came to the tone of the color, I think C1 tended to give better results. The results from Photoshop just seemed to have strange tints to them.

So in the end, I didn't seem to be satisfied with any real improvements in Photoshop. I think I'd be more likely to get a better match in C1 by just adjusting the levels and such. In addition, this custom profile business seems very theoretical. Yes, you can get a profile set up for a shot, but realistically you should have a custom profile for each ISO setting under each different lighting condition. That seems like too much of a pain. I'd probably end up with just a few profiles for different conditions, and then use the one that is closest. I'm not sure that approximating in Photoshop is necessarily any better than approximating in C1. Seems like you'd lose out on the extra flexibility that Photoshop offers.

Finally, when it came down to it, I started thinking about how important the whole idea of precise color matching is anyway. Certainly there are those really art oriented people, who will raise a fuss if the colors aren't exactly as they saw at the time...wanting to be true to the spirit of the original subject and all. Myself, I seem to find myself happy with close approximations. Who's to say that the "true" colors are the best. I can certainly come up with photos that give me satisfying results in C1.

So in the end, it might seem like wasted time, but it was educational, and it was also reassuring to prove to myself that C1 is indeed the right tool for me. It's never bad to go back and reexamine your tools. As you gain experience and knowledge, you may find yourself outgrowing tools that seemed fine before. It felt good to prove to myself that C1 is NOT one of those tools I have outgrown.

So, that was my experience working with custom color profiles. In a few future posts (which I'll really try to get up this week) I'll mention my other year end/new years projects and my Christmas goodies.

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