On spot color prepress in direct plate making process
With the development of printing technology, four-color printing can’t meet the color requirements of exquisite products in some aspects, and the application of multi-color printing is gradually becoming more and more extensive. In the familiar CTF process, multi-color printing can be done by film, printing and proofing to check whether the matching of ink colors and the overlapping of the edges of the adjacent areas between spot-color ink and four-color ink are reasonable. Because the cost is very low, we can modify the documents and film proofing, and repeat experiments until the customers are satisfied. In the computer-to-plate process, what we see before publication is a digital sample, and it will never appear color leakage or double color phenomenon. However, in the printing of the post-process, even if the CTP version is printed, the error is inevitable. This error can only be compensated by Trappmg the document and stamping or removing it according to different situations. Therefore, in CTP process, the prepress treatment of spot color is particularly important.
Generally speaking, the size of trapping is different with different depth of spot color ink; Different matching of spot colors and four colors means different trapping methods.
1) dark spot color meets light color The dark spot color is connected with the light color, and the light color traps the dark color. The value is generally between 0.02 and 0.15mm..
2) Dark spot colors are connected with darker four colors When the dark spot color is connected with the dark four colors, Trapping should generally be done from small to large area, and the value is generally 0.05—0.15mm. In PackEdge software, the trapped 0.05—0.15mm is automatically stamped. In CoreIDraw, the principle is the same, but the processing method is different, which is more troublesome.
3) Color characters on spot colors For the color characters in spot color, regardless of the color matching, the background color should be Trapping by the characters to ensure the shape of the characters is unchanged. In CorelDraw, the characters are treated as graphics, and the same color edges are filled in the four-color layer according to the size of the characters, which can achieve the effect of trapping.
In CorelDraw and Photoshop, the spot color of raster image can be processed by layering or multi-channel, but in PackEdge, because it receives PS, EPS, TIFF and PDF format files, it can directly trap vector graphics and text, but the spot color effect of the image will change, let alone Trapping. Only the masks of different images can be selected and filled with spot colors. For effective images, such as blur, excessive and feathering, they must be redone in PackEdge. Its effect is more natural than CorelDraw and Photoshop, and the excessive ladder is much smaller. Uniform color is the biggest advantage of PackEdge.