One of the great advantages of digital cameras is the ability to get instant feedback on every image you take. Histograms are a key component, ensuring a perfectly exposed image, every time. They allow you to correct exposure issues and perfect your shot in the camera which can dramatically reduce the time it takes to process and ship the image.
The small screens on the back of digital cameras can vary quite a bit in size and quality which means that they are not ideal for assessing the exposure of your image. The good news is that most digital cameras, from point and shoots to pro bodies, give you the option of displaying the histogram when viewing images. The histogram uses numbers to represent your image and thus does not rely on the screen, making it the ideal tool when assessing the exposure of your images.
The histogram is a graphical representation of all of the colors, and their quantities, in your image. The horizontal axis represents all of the colors in the image in numerical order. Zero (black) is on the left, and 255 (white) is on the right. The vertical axis displays the amount of each color. If the line goes all the way to the top, then there is a great deal of that one particular color in your image.
While all of this sounds technical, it’s not necessary to look at every point on the graph. A quick look at the overall curve and the end points will tell you what you need to know.
Ignore the peaks and valleys; instead focus on the overall curve and end points of the graph. If the graph is bunched up on the left side, then your image will be dark. If this isn’t what you want, adjust your exposure and shoot again. If the graph is bunched on the right, then your image will be too bright.
If either end point is cut off (above the bottom line), then there are colors that are not being represented in your image because it is either too dark or too light. Adjust your exposure or your exposure compensation so that the graph is more in the middle. Keep in mind that you may want your image to be light or dark, but if the histogram is cut off, then you are missing colors. Ideally, the end points should be on the bottom line in the corners.
Every image is different, and will have unique histograms, but as a general rule, you will want to keep the bulk of your graph away from the far right (white) side. If the histogram is bunched up too far on the right, your image will be washed out, and it will be very difficult to recover any of the information when processing in photoshop. Spikes on the right side of the histogram, represent highlights in the image. If the spikes are on the extreme right, then you will have white spots in your image, which will be next to impossible to fix in later processing. In general, it’s better to have a slightly underexposed (darker) image, than one that is overexposed, because it will be easier to adjust later in your computer.
Once you shoot an image, do a quick check of the image to see that it is composed the way you want it, and check the histogram to see if the exposure is correct. Do not rely on the image on the screen to give you proper exposure. Check the histogram to be sure. With Practice this will become second nature and you will notice your images becoming consistently exposed properly.