What is a photographic histogram?

Histogram can be used to accurately determine whether a photo is overexposed or underexposed. Experienced photographers can also qualitatively judge whether the exposure of a photo is appropriate by histogram.

What's the use of histogram?

Histogram can be used to accurately determine whether a photo is overexposed or underexposed. Experienced photographers can also qualitatively judge whether the exposure of a photo is appropriate by histogram.

What can't histogram do?

Histogram can't be used as the absolute only criterion to judge whether a photo is exposed accurately or not. It is more difficult to decide whether a photo is "good" or "bad".

What is the histogram?

The black bars on the histogram (dense lines connected together, which look like a piece, can actually be understood as independent lines) represent the distribution of information in the photo. The ordinate (the height of the line column) indicates the amount of information, and the higher the line column, the greater the amount of information; The abscissa represents the brightness distribution of the photo, with the dark part on the left and the highlight area on the right.

How to read the histogram?

The histogram first has two boundaries, namely pure black and pure white. Between these two boundaries, there is a gradual change from pure black to pure white. When we read the histogram, we only look at how much information there is under different brightness (row height).

First of all, we will see if there are any lines near the left and right borders. This information is generally overflow information, that is, it is pure black and white in the photo. If a large number of lines on the left boundary are high, it can generally be judged that there are a large number of underexposed areas in the photo; On the other hand, if the right boundary column is high, it is considered that there are a large number of overexposed areas. This is also the most important function of histogram.

Then, we can have a qualitative understanding of the brightness distribution of the photo by looking at the distribution of the height of the column in the whole transition space. For example, a large number of columns are concentrated on the left side (bounded by the middle of the abscissa), indicating that the whole photo is dark; On the other hand, if the columns are mainly concentrated on the right side, it means that the photo is bright as a whole. Photographers can compare the photo effects they want.

The standard of histogram?

First of all, there is no absolute standard for histogram, but there are some judging principles:

Generally speaking, it is hoped that the peak value of the column will remain in the middle of the abscissa, and gradually decrease to both ends, with the least at the left and right boundaries (preferably only point contact). But at the same time, the line column should not be too far away from the boundary, otherwise the contrast of the photo will be low and the photo will look "gray".

If it is a silhouette or a night view photo, a large number of lines are allowed to cling to the left side, because there are a large number of black areas in the picture.

If it is a high-profile or backlit photo, the column should be on the left. Because these photos are brighter, there are many bright spots in the picture.

Take the histogram in the picture as an example, the line and column just end at the left boundary, that is, there is no overflow and there is a good shadow transition; On the right, you can see that part of the column is near the boundary. This is because some of the white clouds in the photo overflow and become pure white, but the scope is small, which does not affect the photo taking. In the transition area, we can see two peaks, one on the left and the other on the right, and the middle line is low, which shows that this photo has many bright pictures (the sky is bright as a whole) and many dark pictures (the fence in the foreground and the grass in the middle are dark). You can compare the shape of the histogram with the actual picture and carefully understand the relationship between the histogram and the picture.