Printing registration

Many press manufacturers have installed automatic register systems to assist the operator in getting the print back into proper alignment.

With proper registration, there will be no white space, out of margin colors, or confusing overlap of images in the print.

When proofs for each color are generated on separate pieces of film, use of registration black makes crop marks visible on all channels, providing a useful reference for alignment.

The name "All" might not be used in the user interface of a design program, especially outside English language speaking areas.

As a side effect, it is impossible in PostScript to create a normal spot plate with this name.

There is no special rule for the name "All", so PDF creators must include a tint transform that converts to black in some color space, in order to maintain the same appearance as the final printed piece.

Trapping is a method of adjusting areas where two distinct, adjacent colors meet so that press misregistration won't cause white spaces.

The trap width is dictated by the maximum amount of misregistration of the entire workflow up to the press.

[6] This method, using small measured registration marks on both the stone and the paper, is very accurate and simple to do.

This way many runs of different colors can be pulled exactly in line with one another, each of them measured from the same system of marks.

Misalignment in CMYK registration
A registration mark showing a slight misalignment of the printing heads, resulting in subtle color hues visible around the edges of the black area (click image to zoom in).
Knock-out
without trapping 		Knock-out
with trapping 		Overprinting
Comparison of a knock-out with and without trapping, and overprinting for perfect and imperfect registration. Rows are as follows:
  1. The cyan (lighter) plate,
  2. The magenta (darker) plate,
  3. Perfect registration (some monitors show slight misalignment)
  4. Imperfect registration
An example of registration misalignment, note the cyan and magenta plates are not in the exact place. Also halftones are visible on the top area.
A commonly used registration mark. Although it seems black in color the actual value should be C=100,M=100,Y=100,K=100.