It's Almost Fall Foliage Season; Don't Rely Solely On Your Histogram To Keep Individual Colors From Blowing Out And Ruining Your Images

An example of how the red channel is "blown out" but the green and blue channels are fine. 

It's almost time for photographers to get out and photograph the beautiful colors of fall here in the Northern Hemisphere.  Most of us rely on our histograms to keep us from overexposing those once in a lifetime images we want to make.  But there is a danger in just looking at the black and white "luminance" histogram we mirrorless photographers see in our viewfinders and the DSLR photographers see on their LCDs after they make their exposure. Why?  

The "luminance" histogram doesn't show you each of the Red, Green and Blue color channels, only overall average brightness levels.  Some digital cameras have a tendency to overexpose one of the color channels, typically the red or blue one.  If you depend on only the luminance histogram, you may find out later when editing your images that they are not as well exposed as you thought and one of the color channels is "blown out."  Not good.  If you happen to have a “blown out” color channel much if not all of the detail in that color will be lost.  How do you avoid this?  Look at your RGB histogram.  

If your camera can't display a three color channel plus luminance histogram when in the "taking" mode, it probably can in the "playback" mode.  I know the latest Fujifilm cameras have a default setting to display this more informative set of histograms by swiping the LCD.  In the "playback" mode step through your settings to display it and you will see how each channel varies in exposure from how the luminance histogram shows the overall tonal exposure of your image.  An example is the image above.

I think it is worthwhile understanding and knowing that what I think I am seeing in my histogram is not what I may be getting.  If I am traveling to photograph fall foliage (or any other important images I am trying to make), I certainly want to be sure that I haven't blown out the red of the leaves and am left with a featureless oversaturated mess of red blobs.  Of course, this can be applied to all of your photography, not just colorful leaves.

If you are interested in pursuing this a bit more, here is a link to my March 17, 2017 post entitled, "A Histogram is a Histogram is a Histogram."  In that post I show you a couple of scenes and describe how all of this works. The red rose image is especially telling.

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Thanks for looking. Enjoy! 

Dennis A. Mook 

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