Various mainstream color models and their concepts

Various mainstream color models and their concepts
1.1 Normally, RGB has 256 levels of brightness, represented by numbers from 0, 1, 2 ... until 255.

According to the calculation, the RGB color of level 256 can combine about 16.78 million kinds of colors, namely 256x256x256=16777216. Usually also referred to as 16 million or tens of thousands of colors. Also known as 24-bit color (2 of the 24-time Square). the 24-bit color also has a more bizarre term called the 8-bit channel color.
here the so-called channel, in fact, refers to three kinds of light color of the respective brightness range, we know its range is 256,256 is 2 8 square, called the 8-bit channel.
Why do you always use 2 of the time to express? Because the computer is 2-binary, it uses 2 of the time to express the number of colors and some other quantities.

The color channel here is conceptually not a specific thing. We can compare the Mihara shade to three adjustable light lamps of different colors, then the channel is equivalent to the dimming button. For viewers, it's just the image itself, not how the three kinds of shade mix. Just as you care about the performance of the actors in the movie, you don't think about the process of directing the shots. Thus, the function of the channel is "control", not "presentation".
The above is the color channel, and the image channel in the following tutorial is not exactly the same concept.

The support for 16-bit channel colors has been enhanced since the Photoshopcs version, which means that more colors can be displayed (i.e. 48-bit colors, about 281 trillion). RGB has a single luminance value of 2 of 16 square, equal to 65536,65536 three is 281474976710656. But the number of colors that can be distinguished by the human eye is less than 24-bit 16.78 million colors. So the higher the number of colors in the eyes of the people there is no difference.

1.2 How can I tell what color it is from a set of numbers?

for a single R or G or B, when the value is 0, the color does not glow, and if 255, the color is the highest brightness. This is like dimming the lamp, the number 0 is equal to turn off the light, the number 255 is equal to the dimming knob to open to the maximum.

How many RGB values are black, white, red, green, blue, and yellow on the screen?

The so-called Hue refers to the color of the type, respectively: Red orange yellow green cyan blue purple. These seven colors are connected to each other to form a closed ring. 0-degree starting point in X-axis direction, unfolded counterclockwise. The image below is shown below.

If a picture on the screen is yellow Color (especially the screen display, print is different), can not be said to be too much yellow light, but should be said to be too little blue light.

1, the RGB mode is the physical color mode of the display. This means that no matter what color mode is used in the software, as long as it is displayed on the display, the image will eventually appear in RGB mode. Therefore, using the RGB mode is the fastest, because the computer does not need to handle the additional color conversion work. Of course, this speed difference is difficult to detect, but theoretically.

2, grayscale belongs to the RGB color gamut (color gamut refers to the color range).

Because the grayscale is formed, the RGB values are equal. The number of RGB values is equal to 256, then the amount of grayscale is level 256. In addition to pure white and pure black, there are 254 kinds of intermediate transition colors. Pure black and pure white also belong to invert color.

The usual representation of grayscale is a percentage, ranging from 0% to 100%. Only integers can be entered in Photoshop, and decimal percentages are allowed in illustrator and golive.
Note that this percentage is based on pure black.

Since grayscale and RGB are the same, what is the value and percentage? For example, 18% of the grayscale, is the level of 256 levels of gray? Is it 256x18%? Yes, the grayscale value and percent conversion is the approximate value after multiplying, because the grayscale and RGB is "black and white upside down", so 18% of the gray level is equal to 82% of the RGB brightness.
256x82%=209.92, approximately counted as 210, we can first select 18% in the Gray slider, and then switch to the RGB slider to see the value. The following 2 figures:

Note If you do not turn off the color management feature, the grayscale standard in color settings may not be GrayGamma2.2, then the above equation is not true. For example, grayscale standard if is graygamma1.8,18% grayscale conversion to RGB is 218,218,218.

Although there are 256 levels in grayscale, because Photoshop's grayscale slider can only enter an integer percentage, you can actually choose only 101 (0%) Shades of gray from the grayscale slider. You can enter the increment value in the gray slider and then switch to the RGB slider to see: 0% of the grayscale RGB value is 255,255,255;1% grayscale RGB value is the 253,253,253;2% gray level of 250,250,250. In other words, 252,252,252 of this grayscale is not selected with Photoshop's grayscale slider. In contrast, illustrator's grayscale allows two decimal places to be entered, making the color selection much more accurate.

Because the grayscale color does not contain hue, it is a "neutral" color, so it is often used to represent information other than color. For example, we have to talk about the channel, grayscale in which is not as a color model exists, but as a criterion to determine the channel saturation. In later masks, grayscale is also used as a criterion for judging transparency.

> You might ask: if the image doesn't use blue at all, it only uses red and green, does that mean there's no blue channel?

Now click on a single channel to see that each channel is displayed as a grayscale image (not a black and white image).

For red, its distribution in the image is uneven, some places more, some places less. Equivalent: Some places the red brightness is higher, some places the red brightness is lower.

This grayscale image is actually equivalent to the distribution of red light.

In the channel,
White (or whiter) stands for "Bright", "visible", "something".
Black (or darker) stands for "Dark", "invisible", "nothing".

CMYK is a reflective color model, how do we read the contents of the newspaper? It is illuminated by sunlight or light to the newspaper, and then reflected in our eyes, only to see the content. It needs to be illuminated by the outside, if you are unable to read the newspaper in the dark Room.

Similar to RGB, CMY is the first letter of 3 printing ink names: Cyan cyan, magenta magenta, yellow yellow. K takes the last letter of Black and does not take the first letter to avoid confusion with blue. Theoretically, only need to cmy three kinds of ink is enough, they three together should get black. However, due to the current manufacturing process can not create a high-purity ink, CMY added results are actually a dark red. Therefore, it is necessary to add a special black ink to reconcile.

It is precisely because of the problems that may arise in printing that we pay particular attention to the production of images used for printing.
For example, to draw a very fine 0.1 mm line, then if the Overprinter dislocation 0.1 mm, there will be two lines. So how to avoid it?
At this point, you should avoid the use of color mixed colors. The following 2 figures:

The left and right are green, the green on the left has ingredients on the CMYK four colors, then the line drawn with this color will be printed 4 times. The green on the right uses only the C and y colors, which can be printed as long as two times. The latter's chance to overprint errors is naturally much lower than the former. Note that "as long as it is printed two times" does not mean that only through two rollers, but also to go through 4, but only two of the rollers have images printed on it.
This small example shows that when you make a print, the color you use affects the success of your finished printing. In the case of RGB mode, there is no need to be wary of this problem, because the screen is not likely to have a overprinter error occurs.

So what is the color pattern of inkjet printers used by our ordinary families? Will it have overprinter errors?
As previously said, as long as the print is CMYK mode, inkjet printer is also working according to CMYK, which is loaded with CMYK four-color ink cartridges (individual models will be more but the same principle), and the printing press similar. But inkjet printers do not produce overprinter errors, which is why? We said that the printing press paper to go in and out of 4 rollers, overprinter error is in the production between this. Inkjet printers are a one-time printing. So there is no overprinter error.

How can inkjet printers achieve one-time printing?
The inkjet printer arranges multiple nozzles in sequence before and after. So at the time of printing, the first line of paper was sprayed on C, and then the paper moved forward one line, the original first line stopped at the m nozzle was sprayed with M color, while the new blank second line was sprayed on C color. Then the paper moved forward, has sprayed the C, m of the line is now parked in the Y-color nozzle, was sprayed on the Y-color. And the second line was sprayed with M. The new blank third line is sprayed on C. And so on
If we cancel printing at half the time the inkjet printer is printed, we see that the unfinished portion of the image is distributed in a similar effect.

Since the principle of inkjet printers is not complicated, why do large presses do not use this way of printing?
Because this is a very low-speed way of printing, the nozzle needs to have a moving process in each line, which takes time, if the large-face paper takes longer. and the newspaper and so on a large number of printed matter need to be completed in a short period of time, so this printing method is powerless. And the precision is less than the printing press. So, printing and printing, there are a lot of differences between the two. The average number of prints is small, and the quality and speed requirements are not high. Common in personal and small office use. Printing is the opposite.

So, how do we choose the right color model? Let us first clarify the difference between RGB and CMYK two color models:

The 1:rgb color mode is illuminated and exists in display devices such as screens. Does not exist in the printed matter. CMYK color mode is reflective, requires external auxiliary light to be perceived, it is the only color mode of print.
2: The number of colors on the RGB color gamut is much more than CMYK. But each part of the color is independent of each other (that is, non-convertible).
3:rgb Channel Gray-scale image shows a high degree of luminescence, and the partial white in CMYK channel gray scale shows low ink content. But instead.

Various mainstream color models and their concepts