Angle discrimination color difference method
First, the hierarchical method
This method is very practical for black and yellow. Generally speaking, in the four-color version, the black version is mostly copied in short tone, so the level is very small, it is easy to identify; because in most works, the yellow components are relatively heavy, so it seems that the yellow version is full. Very vague, and better recognized. The magenta version and the green version are similar in level. If there is no experience in color separation, it is often easy to confuse this method.
Second, the feature color distinction method
Generally, experienced prepress workers use this method to distinguish them. Because it conforms to the color separation principle, it is highly accurate to use. We know that after the color separation of the filtered color patches, each color version has its basic color and opposite color. For the magenta version, the basic colors are magenta, red, blue-violet and black, and the opposite colors are yellow, cyan, green and white.
Therefore, all red, blue-violet and magenta should have a deep black color on the magenta color separation film. We can find some relevant feature colors, such as red flags, red seals, characters' lips, etc. These parts should be dark on the magenta version and light on the green version. On the contrary, some sky, sea, forest, etc. are light in magenta and dark in blue.
Third, the angle distinction method
This is observed from the color separation angle of the film by means of a magnifying glass. In general, the angle of the yellow version is always 90°. This is done in consideration of the characteristics of the weak color version. Because magenta, cyan, and black are strong color plates, it is necessary to avoid the occurrence of moiré, which is usually arranged at an angle difference of 30° from 45°, that is, 15°, 45°, and 75°.
The angle of the strong color version can be determined according to the characteristics of the original, and there is no fixed angle. The yellow color is a weak color version, and even if there is a moiré, the human eye is not easy to observe. For square dots and circular dots, the worst angle is given when a fourth ideal angle cannot be arranged in a quadrant. Therefore, its angle is arranged at 90 °. Note that since the angular arrangement of the chain points is 0 to 180°, it is another matter for the chain points.
Fourth, the network flower differentiation method
If there is a sample, you can also use the proofs to make a net flower distinction. Place a piece of separation film on the proof sheet and turn it slightly at an angle. Some colored net flowers, that is, moiré, appear in the tonal area. If the magenta net flower appears, the film is a magenta version; if it is a cyan net flower, it is a green version. Why is this?
We know that the smaller the difference between the two dot angles, the larger the square pattern is, the more obvious it is. When a monochromatic film is placed on a sample, its angle is the same as the angle of the natural color in the four-color proof. After the film is slightly rotated by an angle, the difference in the true angle between the film and the four-color proof is small. A small angular difference makes it easy to generate an obvious natural mesh.
This will help us easily identify the color of the film. In summary, we can summarize the quick and effective way to distinguish between different color plates.