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The curve can be seen in many image editing software, whether it is the professional Photoshop or the picture editing function of the mobile photo album. In the final analysis, it is because it is easy to use and is one of the necessary painting techniques.

The use of the curve is also very simple, but many beginners think it is mysterious and complex. I think it must be because of the name-it must be very difficult for a curve to be combined with a picture because it is clearly a line.

Basic principles A photo in rgb mode is usually numbered with three numbers, representing the values of red, green and blue respectively.

For example, 0, 0, 0 means red, green and blue are all 0, which is black. 255, 0, 0 represents red 255, green and blue are all 0, which is red.

The starting point represents 0, which increases gradually to the right and up, and the end represents the value of 255.

The RGB picture is in "plus color" mode, which is equivalent to the superposition of multiple lights. The higher the value, the more lights, the higher the brightness.

The curve can be changed, the number changes, and the color of the photo changes. This is the principle of curve revision.

02. Curve parameters

Channel: when you select "RGB", the curve changes all color values. Because red, green and blue are changed at the same time, the color does not change, only the brightness changes.

Selecting "Red Channel" will only change the red value. Add red, and the color will be reddish. If you reduce the red, the color will be bluish.

Selecting "Green Channel" will only change the green value. If you add green, the color will be green. If you reduce the green, the color will be magenta.

Selecting "Blue Channel" will only change the blue value. If you add blue, the color will be blue. If you decrease the blue, the color will be yellow.

Think about it: how does it change if you add red and blue at the same time? Increasing red and blue at the same time is equivalent to reducing green, so the color tends to magenta.

Enter (horizontal): represents the original value of the photo. You can fix it wherever you want.

Output (vertical): represents the modified value. Pull up increases and pulls down decreases.

Example (1):

Select any point on the curve. Select the RGB channel to pull up, the brightness increases. Choose the red channel to pull up, the color is red.

Example (2):

Now there is a picture. I want to turn it into black. What should I do?

First check with the straw tool, found that the color is 100, 130, 200, then we just need to change the corresponding red, green and blue channel to 0.

Here is an easy way to click on the black straw (black field tool) on the curve, then click on the picture, and the place you click on will turn black. The white field tool turns white, and the gray field tool turns neutral gray.

Take a look at the curve and find that the red 100 (horizontal) becomes 0 (vertical), the green 130 becomes 0, and the blue 200 becomes 0.

03. Common operations 1. Change the brightness to drag the curve up to increase the brightness, and drag the curve down to decrease the brightness.

It is very natural to improve the brightness of the photo through the curve, and there will be no overall whitening, graying, lack of contrast and so on, so the photographer prefers to adjust the brightness with the curve rather than the traditional "brightness / contrast" and "brightness" functions.

Next I will give you a demonstration, the left picture is to use the curve to improve the brightness, and the picture is to use the brightness function to improve the brightness. Which do you think is more natural?

two。 Increase the contrast by pulling down on the left and rising on the right to form an S-shape, which can increase the contrast.

This is easy to understand. It makes the dark place darker and the bright place brighter. This is the essence of increasing contrast. The greater the bending of S, the more obvious the increase in contrast.

3. Reduce the contrast to increase the leftmost end of the curve a little, lower the rightmost end a little, and then pull a small S shape to complete the "film curve".

By doing so, the overall contrast can be reduced without making the picture too foggy.

4. Simply adjust the color to make the sunset of the original image a little redder, you can change the color curve separately.

This article is from the official account of Wechat: photography Research Society (ID:shoujiPhotography), by Zhang Xiaozhang.

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