In prepress platemaking, it is often encountered that there are obviously different color blocks in the image, one of the color blocks is covered by another color block, when printing, each overprint a color, there is often a perfect overlap between the color blocks and the color blocks, this overprint problem caused by machinery must be dealt with before press, we call it prepress leak white.
Fixing the missing white is a very tedious matter, and it is only used to correct the misalignment between solid colors in CMYK images. In general, for continuous tone images such as photos, you should not create a leak white, such as the use of leak white will harm the image quality. Excessive filling of the color block is also unnecessary, and it will produce key lines (or even cross lines) in the CMYK plate. These problems are not visible in the composite channel and will be revealed when the film is output. It can be seen that the filling white will not make the image more beautiful, nor can it be used to solve the mechanical problem of printing registration, and it can only properly cover up the defects caused by overprinting.
The main method of filling the leak white is to slightly expand the color block area, so that there is some overlap between different color block areas, the overlap should be very narrow, in print is not easy to detect its existence is appropriate, general vector software (such as Adobe lllustrator, Freehand, etc.) are using this method to achieve filling white.
Adobe lllustrator patch white method
Adobe lllustrator's Path finder panel under the "Blend/Patch white" last is the patch white button (Trap).
one Three parameters need to be set
(1) Thickness. Thickness refers to the input value of the width of the leak, between 0.01 and 500Points, and the system default value is 0.25Points. Under normal circumstances, the input value is 0.5 to 1Points, and the specific value should be determined according to the error measurement value of the printing machine.
(2) Height/Width. The ratio of horizontal to vertical filling.
(3) Reduce the tone (TintReduction). Reduce the value of the lighter color in the color of the missed white, and keep the value of the darker color to 100%, and the default value is 40%. In order to reduce the obvious dark boundary of the patch white area, the amount of ink can be controlled by reducing the tone percentage.
2. Option parameter
(1) Select Traps with process color to trap white in dark areas; Select Reverse Traps to trap in bright areas.
(2) In Adobe lllustrator, the color selection order of the leak repair white is M, C, Y from deep to light;
(3) When making multiple spot color plates, according to the actual ink color to decide whether to make up the white in the dark or bright area;
The plug-in function \ create \ trap under the Freehand software menu is basically equivalent to the Adobe lllustrator fix white dialog box.
Adobe Photoshop patch white method
Adobe Photoshop blanking is done by spreading the channel colors to each other, and there is only one width option for blanking in the menu \ Image \ Trap. The rules of its use are: all colors extend to black; The light area expands to the dark area; The yellow spreads to cyan, magenta and black; Pure blue and pure magenta extend equally to each other.
This kind of leak white will inevitably produce obvious dark boundary between colors, how to achieve the percentage to control the shade of the leak white, like the vector software Adobe elllustrator to reduce the color option, to control the amount of ink in the leak white? By practice, we believe that the following steps can achieve this effect.
(1) Open an image in a file named "TP".
(2) Under menu \ Image \ Copy as "TP copy" and "TP Copy 2"; First, the "TP copy 2" file is executed \ image \ trapping, and the width is identified as 1Points; Select, cut, and copy all to the TP Copy file.
(3) Get a new layer 1 in the "TP copy" file, press F7 to activate the Layers panel and change the layer 1 mode to Difference mode. Since the difference mode is the absolute value of the brightness difference of the corresponding pixel in each channel, layer 1 and the background will be calculated to give a black window.
(4) After merging the layers, invert the Inverse to get the white background and fill the missing white area. Then select, cut, and copy all files to the TP file.
(5) Change the mode of the new layer 1 obtained by the "TP" file to Multiply, and change its non-filling white is necessary for pre-press processing, but the width of filling white and the setting of reducing the percentage of filling white should be determined according to the error measurement value of the actual printing machine, and the leakage phenomenon of printed matter should be avoided through proper processing.
