Color models

This article describes the color models used by Adobe Photoshop.

The world around us is full of all sorts of colors and color shades. From the physical point of view, color is a set of certain wavelengths reflected from an object or passed through a transparent object. However, now we are interested in the question not about what a color is, what its physical nature is, but how it is possible to get one or another color in practice. With the development of many industries, including printing, computer technology, there is a need for objective ways to describe and process color.

Colors in nature are rarely simple. Most colors are made by mixing any other. For example, the combination of red and blue gives a purple color, blue and green – blue. Thus, by mixing from a small number of simple colors, you can get a lot (and what is quite large) of complex (composite). Therefore, to describe a color, the concept of a color model is introduced – as a way of representing a large number of colors by decomposing it into simple components.

Color circle

One of these models is the color wheel, which has already been mentioned many times before. It is represented in the figure and is called Oswald’s great circle.

Along with the circle of Oswald there is also Goethe circle, in which the primary colors are located at the corners of an equilateral triangle, and additional colors are at the corners of an inverted triangle. The scheme of such a circle is presented below. Contrast colors are located opposite each other.

Color gamut

Before proceeding to the consideration of color models separately, we first consider the concept of color gamut, which will give us an idea of ​​how well one or another color model is well represented by colors. Color gamut is the maximum range of colors that can reproduce or capture a device, or a human eye.

The cathode ray tube of a monitor or television, color models, printing inks and, of course, the human eye have a certain color gamut. Figure 3 shows a schematic comparison of the color gamut of the human eye, the monitor and the printing machine. The color gamut of the monitor roughly corresponds to the RGB model in different variations, the printing machine is CMYK.

So, color in computer technologies, in printing houses, in many other industries related to image processing, is represented as a combination of a small number of three components. Such a presentation is called a color model. Different types of models have different color coverage. This is their main advantages or disadvantages. Reflected and absorbed color is described in different ways. There are quite a large number of color models, but we will focus only on those that are most often used in graphics packages.

RGB color model

This is one of the most common and frequently used models. It is used in devices that emit light, such as monitors, projectors, televisions. This color model is based on three primary colors: Red – red, Green – green and Blue – blue. Each of the above components can vary from 0 to 255, forming different colors and thus providing access to all 16 million. When working with a graphic editor Adobe Photoshop, you can choose the color, relying not only on what we see, but if necessary, specify the digital value, thereby sometimes, especially when color correction, controlling the process of work.

This color model is additive, that is, as the brightness of individual components increases, the brightness of the resulting color will increase: if you mix all three colors with maximum intensity, the result will be white; on the contrary, in the absence of all colors, black is obtained.

It is important to know: The numerical values ​​of the channels in Photoshop mean the brightness of this color. That is, the larger the number, the brighter the channel looks. To better understand this fundamental principle, experiment with the color picker dialog box, entering different values ​​of one channel with the others at zero.

The advantages of this mode is that it allows you to work with 16 million colors at 8 bits per channel (224 colors), and the disadvantage is that when you print an image to print, some of these colors are lost, mostly the brightest and most saturated, also there is a problem with blue flowers.

The RGB color model is considered the easiest to master. The vast majority of lessons for beginners and intermediate users are written specifically for her. But a high level of proficiency in Photoshop involves knowing the basics and the ability to work in other color models.

CMYK color model

Much closer to the color coverage of the printed image is the CMYK color model.

Unlike the previous RGB color model, this model uses the so-called subtractive color synthesis. It uses the parameters of the reflected light. That is, if the color of an object, for example, is blue (Cyan), this means that it absorbs red from white, in other words, it is subtracted from white. If the color of the object is Magenta, it means it absorbs the green color. Finally, if the color of the object is yellow, it means it absorbs the blue color. If the object absorbs all the colors, we see it as black. In the CMYK model, black is called skeleton or key (Key). The abbreviation CMYK is formed by the first letters of subtractive colors.

It is important to know: CMYK color model channels in Photoshop indicate the amount of paint of a certain color. That is, the higher the numerical value of the channel, the darker it is. This is a fundamental difference of this model from the previous one. In addition, since CMYK contains 4 channels, the possibility of more subtle, even jewelry, color correction appears. That is why professional users prefer to perform color correction in this color model.

Preparing an image for printing in a printing house or on a printer also requires the knowledge and ability to work in CMYK, since printing machines, including printers, create images on just this principle.

The disadvantage of CMYK is a narrower color gamut, so some of the colors are irretrievably lost when they are converted from another color model.

Lab Color Model

If with the previous color models the difficulties usually do not arise, then with the Lab model the situation is completely different. Understanding the interaction of color channels in it is a little more difficult. The fact is that in Lab space, color is separated from contrast. In one channel L (brightness) contains information about the details of the image and the brightness contrast. This is almost a black and white version of the image. Channel a covers a palette ranging from magenta (127) to green (-128). Channel b covers the palette from yellow (127) to blue (-128). The zero values ​​of a and b correspond to neutral tones, that is, all shades of gray.

Lab is also called a hardware-independent model. In fact, all the work of Photoshop is based precisely on the algorithms of this color model (although the majority are not aware of this). Lab’s color gamut corresponds to all the colors we see, so almost half of them are not reproduced when printed, and one fifth is not reproduced by the monitor.

Mastering a job at Lab is not easy, but even possession of several methods of work in this space allows you to perform such a correction, which is either impossible to make in other models, or the result obtained in Lab in a few seconds is achieved with great effort and time.

In conclusion, I want to add that whatever color space you choose to work, this in itself does not mean anything. To achieve a good result, you need to clearly know the principles of the formation of colors of each model, and, of course, the basics of working with all the tools in Photoshop.

I wish you creative success!
Author: Evgeny Kartashov

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