Why do I need a Histogram?
What is a Histogram?
A histogram is a graph that shows the brightness of the pixels in your image. The horizontal axis of the histogram goes from pure black on the left side, to the brightest white on the right.
The vertical axis shows how many pixels are in that tone.
How do I see the Histogram?
On Canon cameras, you push the INFO button until it appears.
Nikon uses the Multi-Selector up and down arrows.
Sony you keep pressing the DISP button at the top of the control wheel until it appears.
If you have a different make the simplest way is to look up Histogram in your camera manual. If you don’t have a camera manual you can download a free copy by clicking User Manuals in the menu.
Some cameras give you a general histogram and three others that cover Red, Green, Blue. Now you could get into the weeds and checkout the histogram for each color, but I would just stick to the general dark to light one.
Is it necessary to use a Histogram?
When I got my first digital camera I was confused because the sky was blinking after I had taken a photo, so I turned the flashing warning signal off. It took me a while to figure out that the camera was telling me that the sky was blown out. Meaning the area of the image that was blinking was way over-exposed. If I had known that the histogram gave me information to prevent blown-out images, I would have saved myself years of screw-ups.
How many photos have you taken that look great on the rear LCD screen but not that great on the computer because of an over-exposed sky or lack of details in the shadows? The histogram will show you if the image is over or under-exposed.
If your aim is to get properly exposed images, then the answer to “Is it necessary to use the histogram?” is a definite yes.
How do you read a Histogram?
You need to look at the shape of the graph. An ideal graph is spread evenly between the dark left side and the bright right side. If you take a photo with an ideal histogram your image will be correctly exposed and have great detail.
If the graph is bunched up to the left of the graph the photo will be under-exposed, but not in all cases. If the graph is all the way to the right it will be over-exposed, and again, not in all cases.
Look at the ends of the Histogram. The ends of the histogram are pure black and pure white. At these points, there is no detail just black or white. The aim is to have your graph stop before it gets to either pure black or pure white. If you can do that your image will have detail in the shadows and color and definition in the sky.
Not in all cases
When I said not in all cases, I meant that there are times you want the graph way to the right or left. To get the creative effect you want, the graph needs to be either far right or left.
A couple of days ago I took a photo of a rock (a Geode) on a dark gray table. My aim was to make the table look black, so I exposed the image so the graph was going off the left-hand edge of the histogram. This made the gray table look black, and because I shoot RAW files I was able to bring the rock back to the correct exposure.
Now I could have used bracketing to get the same result. Bracketing lets you take three (or five, seven, or more) images of the same scene. One under-exposed, one correctly exposed, and one over-exposed. You then bring them together in photoshop and use the parts of each image you need.
Mistakes and Pitfalls
Don’t make the mistake of wanting a nicely balanced histogram if your scene is a dark cat on a dark street. Everything will be over to the left and there is nothing you can do about it.
Make sure you are using the correct white balance. If you are using an incorrect white balance setting it will give you false histogram readings. Halfway between pure black and pure white is 18% gray. When you set a custom white balance you use an 18% gray card so the camera knows what the midpoint between white and black is in the location you are shooting. If your camera doesn’t know this the histogram will be off also.
Now you don’t need to do a custom white balance, but it is a good thing to do. Just make sure the White balance isn’t set to tungsten when it should be daylight.
So from now on
You are going to balance your light meter to get a correct exposure. After the photo is taken take a look at the histogram, and adjust your settings if needed.