# Correction by numbers

In this lesson you will learn about the classic way of color correction of images “by numbers”.

This method is repeatedly described in the manuals dedicated to the work in the program Adobe Photoshop. Reception of image correction “by numbers” refers to the classical, basic methods of working with images. Most likely, his age is equal to the age of the program itself, which is about a quarter of a century.

The effectiveness and efficiency of this method is very high. It allows you to make accurate color correction, based on the mathematical relationships and the exact numerical values ​​of the components of R, G, and B, that is, red, green and blue.

Professionals in their work when preparing images for printing often use the CMYK color model, image correction in it can be done with jeweler’s accuracy, especially if you need an exact color matching, for example, the clothes on the photo for the catalog to the original. But to learn how to work in this color model, we need quite extensive theoretical knowledge about the features of different color models. Those interested can read about it in the relevant literature.

The name of the method “by numbers” implies the active use of the Info palette. You can read about it in this article.
You should also be able to find points of black, white and neutral colors.

Step 1. Open the image.

Step 2. We find the points of black and white, as written in the article “Search for the black and white points in the photo.” It should be remembered that bright highlights and reflections of light sources cannot be taken as white points.

Step 3. Create an adjustment layer Curves (Levels). To do this, click on the icon at the bottom of the layers palette and select the Curves from the drop-down list.

Step 4. Now we need to set on the curve (more precisely, on all the curves, since we will work with all the color channels) points corresponding to the one we noted. To do this, click in the marked points by pressing simultaneously CTRL and SHIFT. As a result, two points will appear on the curves of each channel. They are not visible on the general RGB curve.

Step 5. Now turn to Info palette. We look at the color values ​​of our marked points in each of the channels. For white color values ​​should be equal and slightly less 255 (in the range of 240-250). For black, the values ​​should also be equal, but slightly greater than zero (in the range of 5-15). If it is difficult to determine the points of black and white, you should choose colors that, according to logic, should be neutral. These include all shades of gray..

In this case, I chose points that are close to neutral, on the horse’s mane and on the snow. As you can see, the values ​​of the color channels differ from each other quite significantly, which indicates the wrong color balance. It’s time to fix it.

Step 6. Our goal is to make the color values ​​at the marked points equal. Let’s start with the point of white, which is located in the snow. Let’s analyze the values ​​of color channels in the Info palette.

As you can see, you can either reduce the values ​​of red and blue channels, or slightly increase the values ​​of green and blue, slightly reducing, in turn, the value of red. The second option will be correct. It is necessary to avoid a strong correction in one channel, it is better to work with everyone a little bit.

So, choose the average color value. It is calculated as the arithmetic average of two channels with the most different values, in this case red and green. Select the red channel curve. Click the right mouse button on the point in the upper right quadrant. Use the arrow keys to drop the point down, carefully observing the color value in the Info palette.

Repeat the same for other channels. Moving the curve point down leads to a decrease in the value, up to an increase.

Step 7. Repeat the correction for the second control point, that is, the black point.

Step 8. This is the result. As you can see, the color balance is fixed.

The term “correction for memorable colors” is often used. This is the same “by number” correction, but colors are used as reference colors for which the exact ratio of color channels is known. For example, it is skin color, or colors that should be neutral (for example, asphalt, clouds).

Let me conclude with the conclusion that the ratio of the body colors of the body colors (R: G: B) for the skin of a young European-type woman with varying degrees of tan:
Bright hues 1: 0.55: 0.35
Mid tones 1: 0.65: 0.4
Dark tones 1: 0.75: 0.65

Here you will find a table with memorable flowers.

I wish you all creative success!

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