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Four-color printing
As long as the three colors of R+G+B collide proportionally, tens of millions of colors can be generated. Why black? Black can be produced when the ratio of R.G.B is equal, but it is not feasible to produce one color with three inks. In fact, in the design process, black is used a lot, which is actually why four-color printing is used. Another point is that the blacks generated by RGB have a sense of vanity compared to blacks that are blended directly with ink, while the latter feel more solid.
1. With the four-color principle, it is much easier for everyone to accept. IT IS EQUIVALENT TO THE FOUR FILMS AT THE TIME OF OUTPUT, AND IT IS ALSO EQUIVALENT TO THE FOUR CHANNELS IN PHOTOSHOP: CYAN, MAGENTA, YELLOW, BLACK (C, M, Y, K). The changes we make to the channels when we process the image are actually changes to the film.
2. Mesh, outlets, net corners, flat nets and hanging nets. Mesh: per square inch, the number of dots, 175 mesh for commonly used printed matter, 60 mesh to 100 mesh for newspapers, depending on the paper. Special printing has a special mesh, depending on the texture.
1. The format and accuracy of the picture
Modern offset printing is offset printing (four-color overprinting), that is, the color picture is divided into four colors: green (C), product (M), yellow (Y), black (B) four-color dot film, and then dried into PS version, after four times printing by offset press, it is a color printing product.
Printed images are different from ordinary computer display pictures, and the images must be in CMYK mode, not RGB mode or other modes. When outputing, the picture will be converted into dots, that is, accuracy: dpi, the minimum accuracy of printing pictures should theoretically reach 300dpi/pixel/inch, and the exquisite pictures that we often see on the computer feel very beautiful on the monitor, in fact, most of them are 72dpi RGB mode pictures, most of which can not be used for printing. The picture used can not be displayed as the standard, do not think that the picture can be used for printing because it is very beautiful after acdsee or other software, and it is also beautiful after enlargement, it must be opened by Photoshop, and the image size is used to confirm its true accuracy. For example, if the resolution of a picture is 600*600dpi/pixel/inch, then its current size can be enlarged to more than double the use of no problem. If the resolution is 300*300dpi, then it can only be scaled down or the original size, and it can no longer be enlarged. If the resolution of the image is 72 x 72 dpi/pixel/inch, then it must be reduced in size (the dpi accuracy will be relatively larger) until the resolution becomes 300 x 300 dpi, then it can be used. (If you use this function, set the "Redefine pixels" item in the image size option in Photoshop to none.) )
Common image formats are: TIF, JPG, PCD, PSD, PCX, EPS, GIF, BMP, etc
Second, the color of the picture
Regarding some professional terms such as overprinting, overprinting, hollowing, spot color, etc., you can consult some relevant basic knowledge of printing, and here is only some common sense that must be paid attention to.
1. Hollowing out
If there is a line of blue text pressed on the yellow baseplate, then on the yellow version of the film, the position of the blue text must be empty. The reverse is also true for the blue version, otherwise the blue thing is printed directly on the yellow, and the color will change, and the original blue word will become green.
2. Overprinting
If there is a line of black letters pressed on a red baseplate, then on the red version of the film, the position of the black letters should not be hollowed out. Because black can suppress any color, if the black content is hollowed out, especially some small text, a slight error in printing will cause the white edge to be exposed, and the black and white contrast is large, easy to see.
3. Four-color black
This is also a more common problem. Before exporting, it is necessary to check whether the black text in the publication document, especially the small print, is only on the black version and should not appear on the other three-color versions. If it does, the quality of the printed product will be compromised, and when the RGB graphics are converted to CMYK graphics, the black text will definitely change to four-color black. Unless otherwise specified, it must be processed before the film can be exported.
4. The picture is in RGB mode
When an image is output in RGB mode, the RIP system will automatically convert it to CMYK mode output. However, its color quality will be greatly reduced, and the finished product will be light in color, not bright, and the effect is very bad. It is best to convert the image to CMYK mode in photoshop, and if it is a scanned manuscript, it must also go through the process of color correction before the image can be used.