Anomalous reflectance

Why are purple-blue shades so hard to photograph?  This is an issue that I had attributed to my bad camera, or maybe general photographic ineptitude (I have run into people complaining of this issue before).  But this morning when I went to photograph a glorious sapphire/iris blue nail polish, I was disturbed to find the same problem in my newer, fancier camera.  I tried all the white balance options, I tried indoor lighting, I tried sunlight, I tried shade.  All the pictures were coming out primary blue.  And it wasn’t just my cam’s LCD screen– uploaded to my computer, the pictures looked the same.  BLUE!

Searching in google revealed that this is actually a recognized problem in photography.  It’s called anomalous reflectance, which occurs when objects reflect parts of the spectrum which ours eyes are not sensitive to, but the camera is.  The problem is especially pronounced in flowers (e.g. morning glories) that reflect lots of ultraviolet light.  Short of getting a lens filter, there’s no pre-processing solution.  This article provides a nice summary, though it seems a bit dated.  (The article also makes reference to what appears to be a seperate problem that can lead to the same result, that film is calibrated to enhance flesh tones and nature scenes, such that colors like chartreuse and iris blue get misrepresented.  Presumably this problem does not apply with digital cameras.)

So it looks like I am going to have to alter the color balance before posting pictures of this spectrum of colors.  I don’t object to this in principle or anything, it’s just annoying.

Here’s a quick and dirty way to do this in Photoshop:

1. Select everything around the bottle using the magic wand (this is easier than selecting the bottle itself) and then choose Select > Inverse. (If you’re doing this to nail swatches, it may be easier to select the nails directly.)

2. Feather your selection by a few pixels (Select > Feather).  Alternately, select the color range (Select > Color Range, and then click on the color you want to change).  The latter strategy gave more natural-looking results, but either way, the point is to not have a hard edge surrounding the color-altered area, such that the image looks obviously doctored.

3. Go to Image > Adjustments > Color balance.  To make a purple object appear less blue, increase the balance of red, until it matches its real life appearance.

4. Optional: Other alterations may be necessary to achieve the proper color.  In the case of my picture, the color was not dark enough, so I reduced the brightness in Image > Adjustments > Brightness/Contrast.

Here is a before and after comparison of China Glaze Bermuda Breakaway.  On the left is the original shot (which bears a striking resemblance to OPI Dating A Royal); the right side has the color corrected image as it looks in natural light: deep, bright, purple-tinged blue.  As always, YMMV (your mileage/monitor/mind may vary).

This problem is manifest with other pictures I’ve seen of Bermuda Breakaway (I’ve noticed the problem in many purples and blue-purples, but BB provides a nice case study).  Just for comparison, here are pictures of BB from some other sites that usually have color-accurate pictures.  The pictures below have not been altered in post-processing (that is, they are the way the color originally photographed).

Here’s Scrangie’s.  (The pinky nail is a different polish.)

EmpressStephanie’s came out much closer to the real thing. (She reports that using 8 daylight bulbs and extreme white balance on her Canon D40 solved the purple/blue issues.)

Here is tink’s version, taken in sunlight.  Looks a lot like my original photo.

Here is cincyfan’s picture.  There’s more purple in her version, but lightboxes (I assume this is a lightbox) sometimes create a glassiness that is less than ideal for getting a direct shot at the color.

I think I’m detecting a pattern here– lightboxes are better for counteracting anomalous reflectance than sunlight.  I think an experiment is in order…

Tags: Blues, blurples, cameras, photography, purples