PDF Overprint Simulation & Transparency Preview
Check overprint and transparency risks before printing
Check overprint and transparency risks before printing
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Check /OP and /op overprint settings for knockout gaps before printing
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This page contains objects with overprint turned on. The approximate colors in the table below are the colors that overprint on this page.
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About PDF Overprint Simulation & Transparency Preview
Printing lays down each ink on its own plate. By default objects knock out: the ink below is left blank in the shape of the object on top. With overprint turned on, the lower ink is not removed and the top ink prints over it. That is why black text set to overprint on a colored background shows no white gap even when the plates are slightly misregistered.
The trouble comes from output paths that ignore overprint. In the overprint tab, this tool lists objects that were actually filled or stroked while /OP or /op was on. In the transparency tab, it covers in red every page where a blend mode, reduced opacity, soft mask or overprint setting is actually used.
What the overprint tab tracks
It reads each page's content stream in order, pushing and popping graphics state with q/Q and following the /OP (stroke) and /op (fill) values of any ExtGState applied with the gs operator. When a paint operator such as f or S runs while one is on, the object is recorded with its current color. An overprint setting that is defined in an ExtGState but never used does not appear.
Colors shown are approximations: CMYK goes through a simple RGB conversion and spot colors are shown by the tint in their alternate color space. Overprint inside nested Form XObjects and on images is not checked in this version, so an empty list does not prove the file uses no overprint.
The transparency tab: finding pages with risk signals
For each page it looks for /BM (any blend mode other than Normal), /ca and /CA (opacity below 1), /OP or /op and soft masks (an /SMask other than /None) in ExtGState resources, and counts how many times gs actually calls them. It also catches image soft masks, common in drop shadows: when an image XObject has an /SMask (alpha channel), it counts how many times Do paints that image. Flagged pages can be downloaded as a PNG with a translucent red wash over the whole page. It points you to a page to open, not to a specific shape. Whether to flatten transparency before sending depends on the printer's spec; the guide “PDF/A and PDF/X” covers what PDF/X versions allow.
Worked examples
White text set to overprint
- Input
White text (CMYK 0,0,0,0) on a blue background, fill overprint /op true- Output
Listed in the overprint tab as a white fill object
White has no ink, so overprinting it prints nothing and leaves the background untouched. On a press that honors overprint, the text disappears. A preview that ignores overprint shows it normally, which is why this slips through.
K100 text on a yellow background
- Input
9 pt black (K100) body text on a yellow (Y100) background, fill overprint on- Output
Listed in the overprint tab as a black fill object
With overprint honored, the yellow stays under the text, which prints as Y100 + K100 with no white gap even if plates shift. Output that ignores overprint knocks the yellow out in the shape of the letters. The text shows either way; what differs is how well it tolerates misregistration.
How to use it
- Add the print PDF.
- Check the object list in the overprint tab and the highlighted pages in the transparency tab.
- Fix anything unintended in the design source and export again.
Frequently asked questions
Does it show exactly what will print?
No. It is an approximate report built by tracking graphics state and does not reproduce a RIP's separations. Do the final check with the separation preview in your design app or at the printer.
Is overprint on black text a problem?
Usually it's intentional: small K100 text printed over a colored background hides misregistration. The ones to check are overprint settings on white or very light objects.
Why does the transparency tab paint the whole page red?
It only decides whether a risky graphics state is used on that page; it does not work out which shape it applies to.
Sources
Last reviewed: