1: RGB color mode is luminous and exists in display devices such as screens. Does not exist in printed matter. CMYK color mode is reflective and needs external auxiliary light source to be perceived. It is the only color mode of printed matter.
2: There are many more colors in RGB color gamut than in CMYK. However, some colors of the two are independent of each other (that is, they cannot be converted).
3: The white color in the RGB channel grayscale image indicates high luminous degree; Whiteness in the grayscale image of CMYK channel indicates low ink content. On the contrary.
Pay special attention to Article 2: Some colors of the two are independent of each other (that is, they cannot be converted). As shown in the figure below, the big green circle represents RGB color gamut, and the small blue circle represents CMYK color gamut. This large and small indicates that the color gamut range of RGB (that is, the number of colors) is larger than that of CMYK. However, after the color mode is changed, only the colors in the mixed area can be retained, and the colors in the RGB-specific area and the CMYK-specific area will be lost.
This means that if you use RGB mode to make printing images, then some colors you use may not be printed. Generally speaking, some bright colors in RGB cannot be printed, such as brilliant blue and bright green. If you print directly without modification, the printed color may be very different from the original one.
Similarly, the following is a comparison of an image made in RGB mode after conversion to CMYK mode, as shown in Figure 2 below:
It can be seen that some of the original bright colors are dimmed, which is because the color gamut of CMYK is smaller than RGB, so some colors are lost after conversion.
Note that if you change the CMYK mode to RGB mode at this time, the lost colors will not be found.
it's like a 2-liter cup filled with water, and then it's poured into a 1.5-liter cup, losing .5 liters. Even if the 2-liter cup is poured back later, the actual content in this cup is only 1.5 liters.
therefore, don't change the color mode frequently. Changing once is equivalent to pouring the cup once, and some water may be lost.
Although theoretically RGB and CMYK will lose some colors when they are converted to each other, when they are converted from CMYK to RGB, less colors are lost, and it is sometimes difficult to see the difference visually. However, the conversion from RGB to CMYK color will lose more, and most of the vision can be clearly distinguished. Therefore, it is customary to say that color is lossless when CMYK is converted to RGB. In fact, what this statement really means is that CMYK is converted to RGB rather than RGB to CMYK.
After understanding the above, we have an idea about how to choose the color mode of the image:
If the image is only displayed on the computer, use RGB mode, so that a wider color gamut can be obtained.
if the image needs to be printed or printed, you must use CMYK mode to ensure that the printed color is consistent with the design.
from then on, whenever we want to start making new images, we must first determine the color mode.
At present, we focus on the design and production of web pages. Because web pages are generally only displayed on the screen, we can use RGB mode comfortably.
so, can RGB images be printed directly?
Yes, you can directly output an RGB image to the printer in Photoshop, and the system will automatically switch the color mode in the middle.
However, it is not recommended to do this, because of the color gamut problem mentioned earlier, the printed image may be different from the colors in the design.