Accurate exposure is the premise of obtaining ideal photos. In some cases, when we can't get the correct exposure through the screen or viewfinder, we need to shoot by judging the histogram.

Histogram plays an important role in the later stage, which can help us to judge the exposure information of the picture, balance the exposure and control the tone. At the same time, if you want to learn retouching and color matching formally, you need to start with understanding the histogram.

1. Cognitive histogram

We divide the photo brightness from 0-255 into 256 values, and the higher the value, the higher the brightness. 0 stands for pure black area, 255 stands for white area, and the middle number is gray, with different brightness.

The histogram is divided into five regions from left to right: black, shadow, midtones, highlights and white. The horizontal axis represents the brightness value from 0 to 255, and the vertical axis represents the number of pixels with corresponding brightness in the photo.

Highlight: bright area

Shadows: dark areas

Midtone: the area where the color scale value is close to 128.

2. Judge the histogram of exposure

Early stage: different cameras have different function keys to call up the histogram. Canon can call up the histogram by pressing the "info" key, which can be used to test the exposure during shooting or view the exposure information of photos after shooting.

Later: the histogram can be directly seen in the upper right corner of LR/PS retouching interface to assist color matching, but now many mobile phone retouching software can also view the histogram.

Generally speaking, the pixel peak exists near the middle tone position, and the photos whose edges are not "trimmed" with black and white fields are exposed normally. Histogram can judge the exposure and tone of a photo, but it can't be used as a basis for judging the quality of a photo.

The histogram of each photo is almost different. "Correct exposure" is not equal to "ideal exposure", and the similarity of shooting styles is varied.

Step 3: Tone

Tone, also known as "tone" of photos, refers to the relationship between light and dark levels, contrast between reality and reality, and light and dark colors of photos, which is of great significance in later retouching and color matching.

Color has three characteristics, namely hue, saturation and lightness. If you don't want to keep the brightness of the first two, then a color photo will become black and white, and there are only three colors in the picture: black, white and gray.

Tone is an important expression means of picture composition, atmosphere contrast and emotional expression. Shade can be divided into bright tone, middle tone and dark tone according to the difference of light and shade. According to the breadth of brightness distribution, it is divided into long tone, medium tone and short tone, and according to contrast, it is divided into soft tone and hard tone.