A: In Photoshop, the setting of four-color black is very special. As far as Photoshop 7.0 is concerned, the default black mark of the software is always: C75 M68 Y67 K90, which is really a very difficult to understand number- Someone has asked this question recently, so I'm writing this article, and everyone is welcome to discuss it.
In fact, the default black in the software, Photoshop is initially set in LAB mode, the value is L0 a0 b0, this is the calculated value in the software system, and the RGB color R0 G0 B0 is the same as L0 a0 b0 , So this color is also an accurate "black" color. But the interesting thing happened to the CMYK color: in the CMYK color, K100-that is, the single black usually said can not accurately express this "system black", in the RGB (Lab) color larger than the CMYK color system In the department, K100 is just an incomplete dark gray, and this dark gray is reddish! —— Do n’t be surprised, this is true in the printing house. No matter how many expensive black (K) inks are used by printing masters, the effect of printing is always far from the black on the RGB (Lab) color system, and Still reddish. Regarding the reddish point, we can look at the "gray" part of a large number of prints-careful and long-term observation will reveal that they are all impure gray-red.
Now we can easily understand why there is this puzzling value in Photoshop: C75 M68 Y67 K90, even if the single black is not enough black, then add more pigments, it turns out that when CMY and K are shared, they can get more The full black effect, and at the same time to correct the unpleasant "reddish tone", the CMYK color system has added about 8 percentage points of cyan (C) ink to balance, which is really a simple and effective method.
If you are interested, we can also discuss the color cast of black (K) ink in more depth: when black ink (with white printing ink) is washed lightly (note that it is not reduced), single black (K) ink is Blueish tones, but as the dilute diminishes, the color cast will slowly shift to blue-purple blue-purple-purple-red.
But why is there no blueish color in the print? We can use a magnifying glass to look at the gray colors in the printed matter. In fact, they are not produced by diluting the white printing ink, but by 100% black ink. It is printed by reducing the screen, so they all show the darkest time. The color cast: red tone.
The last two points to add are:
All grayscale colors of single black are strictly reddish, so in Photoshop, to get the ideal grayscale color, it is best to add a certain proportion of cyan (C) color;
For text, we all know that multi-channel black can be easily printed and pasted, so when designing (printing) text (especially small print) in Photoshop, you must only use 100% single black.
If there is a gray block, it will be sent to the development company to say that there will be dots when the gray strips are sent out. The file is K20, and the dots cannot be seen on the display. The color depth is probably controlled by the density of dots. A color block is displayed on the screen, but the printing is based on dots. If you look at it with a magnifying glass, the color of each dot is actually solid, but their distribution is dense and dense. How can you make a gray that is not white, it is recommended to use non-graded spot colors.
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