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Beginner’s Guide To Histograms

Updated: May 21, 2019

You may have noticed a peculiar graph on your LCD screen when reviewing a photo you just took. This is the histogram and you use it to determine that your photo is exposed properly. The proper exposure cannot be evaluated by looking at the image on your LCD screen. That is because your camera’s menu sets the brightness of the screen.  And while it is possible to fix the exposure in your editing software, you want to get it close to right in your camera. As you will learn later in this blog, sometimes you can’t recover lost details in your photos even in Lightroom, etc. 


The histogram on your camera’s LCD screen is a graphical representation of the pixels exposed in your image. (You may have to dig into your manual to find out how to enable the histogram on your LCD or Live View screen)  A pixel is the smallest unit of color displayed in your image. Your typical camera sensor has 16-24 million or more pixels. (megapixels). 


There are 256 tones of color ranging from black (0) to white (255). All other color tones fall somewhere in between these two. Your camera graphs the color tones out on the horizontal axis of the graph. It shows black and darker tones on the left side of the graph with white and lighter tones show on the right side. The height of the vertical axis of the graph indicates the number of exposed pixels of a particular tone. 


The general shape of the curve displayed in the graph will be different from image to image. Rarely will you see the typical bell curve rising from baseline on one side to the highest point in the middle of the graph, then dropping back down to baseline on the other side.  The shape of the graph should not concern you but rather, that it is not shifted predominantly to the right side or left side of the graph. You do not want a tall skinny spike pressed up hard on either side. 


This is one of the rare times you will see a bell curved histogram, located in the upper right in this screenshot from Lightroom. Comparing the photo to the histogram, you see that this is a brightly sunlit view, mostly mid tones with very little dark or light color tones.

Your image will be underexposed when the curve of the histogram is shifted to the far left side. It will appear dark. If shifted to the far right side, it is overexposed and will appear light or white. This shift to the extreme left or right leads to what we call clipping, especially when it is to the right, the overexposed, side. We also describe this as being “blown out “. This is undesirable because when the highlights in an image are clipped, we lose the details in that overexposed area. They are irretrievable. 


This is an example of an under-exposed image, as seen in the photo and in the histogram in the upper right corner. You can see the curve bunched up against the left side of the histogram.

This is an example of an over-exposed photo. You can see the curve bunched up on the right side of the histogram.

This is the most appropriate point to talk about the “blinkies“.  When you are reviewing a photo you just took, and you noticed the histogram curve is way over to the right side, you may see a black and white blinking in portions of your photo. This is the “blinkies”;  the areas blinking are clipped. I  know that this is properly called the “Highlights Alert” but” blinkies” is more fun to say. On some cameras you have to enable this function; on some, like my Canon T6i, it is always enabled.


So now you know how to analyze the histogram, what do you do with that information?  Since your goal is to attain a good exposure in your image, you adjust your camera as needed towards achieving that end. The quickest and easiest way is to use your Exposure Compensation control. (I explain this in my blog, My Exposure Triangle Has 5 sides….) https://www.sharetimsphotos.com/blog/my-exposure-triangle-has-5-sides


Adjusting this control while looking at your Live View image before you take the photo will move the histogram curve to the right or left, depending on how you adjust the control. When satisfied that your image won’t be over or underexposed, take the photo, then bring it back up in Playback mode to review it. If you are not satisfied with the histogram, go back to Shooting mode, adjust the Exposure Compensation control a little more, then re-shoot the photo. While this sounds time consuming, histograms allow you to get an overview of the entire image quickly, letting you decide whether you need to retake the photo.


The histograms discussed above are referred to as the Brightness histogram; just to mention it there is also an RGB histogram. It functions in the same fashion except it is for the 3 primary colors, red, green, and blue. It will help you analyze the levels of the colors to prevent blowing out any of the colors. At least in my camera, go into the menu and pick either the Brightness or RGB histogram. You may never use it but you should know about it.

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