Avoiding Histogram Combing
by Brenda K. Hipsher – January 17th, 2014
Histogram combing is a phenomenon that digital photographers want to avoid whenever possible. Histogram combing occurs when an already processed file is adjusted. This phenomenon is one way to illustrate how important it is to use a calibrated and profiled monitor to edit Raw files you plan to send to a lab for printing.
Here’s a JPEG processed file with the curves histogram showing from a file I adjusted on a calibrated monitor from a Raw capture. Note that the histogram is smooth in its appearance with no gaps in the graphical representation of the image.
I processed this file to a JPEG before adjustment and did my edits on the processed file in the example below. Note the “combing” effect that is present in the histogram for this image. Pieces of information are missing from the file when adjustments are made after the files is processed.
If your monitor is not properly calibrated and profiled when you make your adjustments in Raw format before processing the image any adjustment to the processed image can cause damage to the file. Information may be missing that cannot be recovered after the file is processed.
Recently I spoke to a photographer who said she was not concerned that her monitor was not properly calibrate and profiled because she paid her lab to do the final corrections. The challenge is that when the Raw capture is processed and edits are performed on the processed file, damage can occur.
Let’s say I performed my edits on a monitor with the wrong profile. The image below looks like I want it to look. So I send it off to my lab for printing. The photo below is what i see on my display, the one that is not calibrated and profiled. I have warmed the image, flattened the contrast. Here’s what it looks like on my monitor.
My uncalibrated monitor is very bright, contrasty, and not set to D65 white point so it’s cooler or bluer than my lab’s calibrated and profiled monitor. When they open the file they see something like this!
Now remember I’m paying these folks to color correct my images. So they’re going to go to work on that JPEG file I sent to them and guess what? They’re not working on my Raw file. They’re working on a JPEG. They will do their best to try to get back to my intended image but sometimes that’s not even possible. And if they do, the editing on the JPEG can damage the file and leave gaps in the data that is sometimes referred to as histogram combing.
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