In this post I will demonstrate how to check for proper skin exposure both in-camera and in Photoshop using the built in histogram tool.
I used to get faked out by the LCD screen on my 5D all the time. Everything would look great on the screen, but I would get it home and find that it was dark and muddy to the point where no amount of Photoshop was going to fix it. Eventually, I heard about using the camera histogram to ensure good exposure, and it made all the difference in the world.
All was well until I started doing portrait photography using off camera flash. I could see by the histogram that nothing was blown-out or too dark, but I found that it was very difficult to tell for sure that your subject’s face was correctly lit.
Getting the exposure correct on your subject’s face is crucial to maintaining good skin tones. If you shoot in RAW, you do have some leeway. It is possible to come back in and adjust the exposure a bit using an image editor. But in my experience, if I am more than 1/2 stop or so under or over-exposed, it’s difficult to get the skin color right, it starts to look unnatural.
I realized that I was going to need to get better at figuring out which part of the histogram represents the face, and lucky for me it turned out to be pretty easy.
I should start out by mentioning that there is already a ton of good information on the web about histograms. A comprehensive technical description would be a very long and dry read, so I will limit my post to information related to using the histogram to make exposing portraits easier.
Your Camera’s Histogram
Most camera histograms look something like this:
The Zone System
Notice that the histogram is divided into five segments, those segments are related to Fred Archer and Ansel Adams’ Zone System. Their system, among other things, created a ten point scale to numerically represent 10 shades of grey, from the blackest black to the whitest white. Camera makers have abbreviated that scale to just five points.
Proper exposure of skin varies from person to person. If you are shooting a Caucasian person with very fair skin, proper exposure will be somewhere around zone 7. By way of example, this is my Canon 5D (classic) histogram:
Evaluate your histogram from let to right, (left = shadow area ~ right = highlight). The two big spikes on the left represent the darkest parts of the image, the taller the spike, the higher percentage of that shade of gray in the image. In this case, the two big spikes at the start of the histogram represent her sweater, the bush behind her, etc.
The smaller section in the middle is your mid-tone range, which in this case is probably mostly located in the city scene behind her.
Keep moving to the right and you see two spikes that are right next together. One of these two spikes is your subject’s face, the other they sky behind her. It’s really hard to tell with this cell phone shot of my histogram, but in real life it was easy to see that the face was slightly darker than the sky, which means that the first spike is her face, and it appears to be more or less properly exposed as it falls midway between the fourth and fifth segments. This is just about where you want your face spike to be for a white person. If you were shooting a darker skinned person, you would probably want to have that peak closer to the middle of the histogram.
The Photoshop Histogram
(click for larger image)
Hitting Ctrl+M brings up the Photoshop curves tool which includes a handy histogram. The Photoshop histogram layout is almost identical to your camera’s except that they’ve abbreviated it even more to just four segments, so you have do a little mental conversion. If you open the larger version of the file it’s a little easier to see what I am talking about. Take a look at the diagonal line moving across the histogram and notice that little circle. That circle appeared when I hovered my eyedropper over the highlight side of her face near her cheek. You can see that it falls just about 3/4 of the way between third and fourth segments, in Photoshop’s histogram, this is about where you want to be for white skin.
The nice thing about the Photoshop histogram is that you don’t have to guess where the face is, you can click the little widget in curves (looks like a finger with two horizontal arrows) and hover over your image, you will see a circle on the histogram giving you it’s exact position on the scale.
That’s it for today, please leave any question in the comment section and I will do my best to address them. If you like The Napa Photographer, please pass the link along to as many people that you think will benefit from it.
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