Let's recall the histogram, as shown below. The horizontal X-axis direction indicates the absolute brightness range from 0 to 255. The vertical y-axis direction indicates the number of pixels. Like a histogram, the Y axis sometimes does not fully reflect the number of pixels. And no statistics are displayed in the color scale tool.
Open the picture on the left below, which is a campus landscape taken in a university. Use the gradation command image >: adjustment > gradation [[〖CTRL〗L] l], as shown in the gradation setting box on the right in the figure below. You can see that it is very similar to the histogram in the last lesson. Note that there are three small arrows below (red 123 in the figure). Their positions correspond to the three values in the "input color scale" (green 123 in the figure).
Among them, the black arrow represents the lowest brightness, which is pure black, which can also be said to be black field. Then you can imagine that the white arrow is pure white. The gray arrow is the middle key. This representation is actually similar to a curve, except that the control points can be arbitrarily added to the curve of the middle tone, while the color scale is not. So the color code is not as flexible as the curve in function. The automatic summation option in the color scale setting box is the same as the function in the curve setting box.
Pull the white arrow to the left, the third value of the input color scale above the straight line drops to 200, and the observed image becomes brighter. As shown in Figure 2 below. This is equivalent to the improved synthesized brightness in the last lesson, which means that the brightness of 200 to 255 has been synthesized. What is the combined brightness? Merge to 255. Because the white arrow represents pure white, it must be raised to 255, and then the brightness stays at 255. Form the effect of merging highlighted areas.
Similarly, moving the black arrow to the right is to merge the dark areas. As shown in Figure 2 below.
The gray arrow indicates the midtone distribution ratio between the black field and the white field. If you move to the dark field, the image will become brighter, because the distance from the black field to the middle tone is shorter than that from the middle tone to the highlight, which means that the middle tone is more inclined to the highlight, so the image becomes brighter. The position of the gray arrow cannot exceed the range between the black and white arrows.
The output color scale at the bottom controls the highest and lowest brightness values in the image. If the white arrow of the output color scale moves to 200, it means that the brightest pixel in the image is 200 brightness. If the black arrow is moved to 60, it means that the darkest pixel in the image is 60 brightness.
Now do an exercise, as shown below. Match the upper curve shape with the lower color scale shape.
That's all about color scale in Photoshop, and I hope it will help you.
Source: Designer Colorful