A histogram is a chart based on the tonal distribution of pixels in a picture.
From the left to the right (horizontally) the brightness is indicated, and from the bottom up (vertically) the amount of the photo area of a particular tonality. It is often said that vertical columns simply show the ratios of the number of pixels of a particular pitch. That is, the diagram shows how much light or dark shades prevail in the picture, how many green or red or other shades of colors in the picture are larger. Histograms are different. In photography, basically, three types are used:
General exposure histogram (which is shown below).
The histogram for each of the three primary colors, such a histogram is often called RGB – red, green, blue – red, green, blue (as in other examples)
Hybrid histogram for the general exposure and for the primary colors (often, just a RGB histogram is superimposed on the histogram of the exposure).
How to use the histogram
The histogram shows how many dark or light areas in the image, what is the overall balance of the exposure of the image.
The histogram is often divided into 3-4 parts. Part of the histogram from the very left edge is called “shadows” or dark tones, since this area shows how strong the dark areas of the image are. The rightmost part of the “lights” or bright colors, so this part shows how many bright areas on the histogram. The middle is “penumbra” or middle tones. The rightmost part is sometimes called the area of illumination, if in the extreme right corner there is a splash on the histogram, then, most likely, the photo is reexposed.
What is useful histogram?
With its help it is easy to control underexposure (underexposed image) and overexposure (overexposed). When overexposing, the peak (top on the diagram) will be visible on the right side of the histogram, and under underexposure a peak will be observed on the left side of the histogram.
Accurately adjust exposure
Control the color channels in the photo. Using the histogram, you can determine the color saturation of the image.
Control the contrast. By the histogram you can easily guess how much is a contrast picture.
What should be histogram?
The only answer to this question does not exist. In the ideal case, the type of histogram should resemble the bell shape (when I was studying at the institute, this shape was called Gaussian). In theory, this form is the most correct – after all, the image will have few very bright and very dark objects, and the middle tones in the photograph will prevail. But as practice shows, everything very much depends on the type and idea of the photo itself. A histogram is a purely mathematical description of photography (art), and as you know, it is very difficult to describe beautiful things mathematically, all the more so with the help of such a simple method as a histogram. Therefore, it is not necessary to bring a snapshot to a template view according to a histogram. The histogram must be used simply as an additional tool when creating a photo.
When do I use a bar graph?
Personally, I use the histogram in only two cases – when I need to check the exposure of a picture in bright light, when the picture itself is practically not visible on the camera display. This may be the conditions of the summer beach or the bright sun in the mountains. Under such conditions, it is simply not visible what is in the picture, because I look at the histogram in order to estimate the deviation of the exposure. And, secondly, I use the histogram when editing photos, it is very convenient to determine the key in which the photo was taken according to the histogram, and sometimes to adjust the photo by adjusting part of the histogram curve. For example, sometimes I just take the “lights” in the histogram and move them to the left with a slider – I move in the shadows, the photo is obtained without overexposure. Such a histogram, as in the examples in this article, gives ViewNX 2.
The histogram is a useful tool for the photographer. To use a histogram or not – you decide, you can do fine without it, or still understand its properties and use it when processing a photo or adjusting the exact exposure.