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 Replies: 7 / Views: 1,802 |
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Pillar of the Community
United States
4132 Posts |
For a while, I've had a sneaking suspicion that I'm not really getting the right color when I'm photographing red cents, even after careful white-balancing. Instead of a typically pinkish copper color, they've come out somewhat golden. I knew it wasn't my display - it looked the same on a number of displays of different kinds (all of which I had properly calibrated and profiled). Sometimes I've compensated for the color problem manually, or just ignored it, as the color was generally pleasing and not distracting. Today I finally got around to testing my hypothesis that my poor pennies were suffering from metameric failure. The problem could occur almost anywhere in the chain (the light source, the diffusors, the optics, Bayer filter on my camera's sensor, the RAW processor, the display profile, the display itself, my eyeballs, my brain...) but I had mostly eliminated a few of those possibilities, and one stood out as an obvious likely suspect.  Copper Lighting Test - Jansjö by CaptainFwiffo, on Flickr  Copper Lighting Test - Speedlite by CaptainFwiffo, on Flickr The first shot was taken with my usual Jansjö LED light setup with smile directors. The second replaces the LED lights with a Canon 430EX II Speedlite flash. The lighting setup wasn't designed with the flash in mind, so they lighting isn't quite an exact match, but it's about as close as I can get it with some minor exposure adjustments in post. Each was separately white balanced (the coin is sitting on GretagMacbeth white balance target). Other than that, they were given identical treatment. The one taken with the flash is clearly much closer to the natural pinkish color of a shiny penny. Most white LEDs are actually blue LEDs with a yellowish phosphor which gives them an overall white color that looks pretty similar to other light sources (tungsten/incandescent light in the case of Jansjö LED lights). However, two light sources can look similar or identical in terms of color while having completely different spectra. In this case, it appears that these LEDs are (as might be expected from their design) deficient in the red parts of the visual spectrum that are important for giving copper its characteristic pinkish orange hue. The flash, on the other hand, has a fuller spectrum and a team of engineers making sure its color reproduction is accurate. I'll probably eventually either switch to using a flash, or create a custom camera profile that compensates for the deficiencies of the LEDs. |
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Moderator
 United States
23522 Posts |
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or create a custom camera profile that compensates for the deficiencies of the LEDs.
Probably the better course of action, given the far greater flexibility of the LEDs in compensating for necessary positioning. I wonder if that would change depending on what diffusion you might be using at the time? Probably not much, as long as the diffusion material didn't change. My guess, either way, is that this is probably more a copper/gold problem than a silver/nickel one, but a comparison on a given nickel/silver coin using both old and new profiles might be revelatory. |
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Pillar of the Community
 United States
4132 Posts |
Different diffusion materials could absorb and reflect different parts of the spectrum while appearing similar colors. Things like air and interstellar dust, for instance, are known to scatter blue light while favorably transmitting redder light. But my diffusors were the same between these two shots, so it's probably not a big factor in this case.
I will try making a custom profile with my ColorChecker chart at some point in the near future. My only concern is that I have different Jansjos from different batches and maybe their spectra is different enough that they're going to give me trouble.
I have noticed that my cupronickel and silver images look quite dramatically different; I had assumed that it was just that seeing them side-by-side in a calibrated way made the color/brightness difference more apparent, but maybe the lighting is exaggerating the difference.
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Pillar of the Community
United States
4132 Posts |
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Pillar of the Community
United States
4037 Posts |
From all the testing I've done, I can't tell the difference between any light source color-wise given a careful white balancing. That said, keep in mind that all white LEDs are actually fluorescent lights that come with all the variability that fluorescents have, and since they are relatively new it's not clear all the bugs are worked out yet. I've never seen a spectral density plot for the Jansjos but it may be they are a bit peaky or have troughs at some wavelengths. But again, I have not seen any of these issues. I remember early on SD complained that my gold coins looked green, but they actually were green! Ever since then I've been fairly careful with color balancing on critical images and have had good luck with the Jansjos. Diffused, of course, to avoid local sensor overdrive...
Contact me for photographic equipment or visit my home page at: http://macrocoins.com |
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Pillar of the Community
United States
4132 Posts |
Well, another factor, and maybe the biggest difference between your setup and mine is the RAW processor. You're using Canon DPP, IIRC, and I'm using Adobe Lightroom. If I used DPP (or one of the Lightroom profiles meant to match Canon's) I might show less difference.
I'm going to keep experimenting with custom profiles, which ought to have the most potential and shows the most accurate result to my eye in this case.
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Valued Member
Australia
64 Posts |
Just a thought, would a red diffuser make any difference?
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New Member
United States
16 Posts |
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For a while, I've had a sneaking suspicion that I'm not really getting the right color when I'm photographing red cents, even after careful white-balancing As a commercial photographer I can tell you that there are a ton of factors that effect the color profile of an image. The lights you use, the ambient light, the background (spill/reflector), the camera, the camera settings, the lens eq, and other a whole list of other things before the image ever gets to your computer. Depending on the system that you use, creating a custom white balance will help. Of course this will change every time you move set up or the ambient light in your room changes. It will also change depending on the reflective properties of the coin that you are shooting. |
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Replies: 7 / Views: 1,802 |
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Posted 02/20/2013 7:35 pm
