Bring to front / Send to back

Introduced in pdfToolbox 10, the two following fixups make it possible to change the order in which graphics objects on the page are stacked:

  • Bring to front
  • Send to back

There is one option in these fixups that needs to be configured in order for the fixup to be useful: the "Apply to:"  option defines the objects whose stacking order relative to any other content on the page shall be changed.

"Bring to front" moves all graphics objects found by the "Apply to" filter in front of all other graphics objects on the page, or, in other words: they will be painted after everything else on the page has been painted. The stacking order of all moved graphics objects relative to each other will be maintained.

"Send to back" on the other hand moves all graphics objects found by the "Apply to" filter behind all other graphics objects on the page, or, in other words: they will be painted before everything else on the page will be painted. The stacking order of all moved graphics objects relative to each other will be maintained.

Example: Bring "Cutline" to front

A simple example for making use of the "Bring to front" fixup could be to move graphics objects to the front that must not be overlapped by anything else. This could be the case for a cutline, to make sure its visual appearance is not impacted by other graphics objects, and is the same as the geometric form described by the vector path (digital cutting devices typically use the path of a certain spot colored vector object – and not its visual appearance on the page – to determine where to cut through the printed substrate).

The screenshot below shows a typical configuration:

Example: Cover "ink free" glueing area with opaque white and bring "ink free" marker to front

For packaging production it is common that the printed surface after cutting and folding has to be glued at certain parts. In some cases, as glue may not stick perfectly well on areas where printing ink has been applied, it is necessary to ensure that no printing happens in the area where glue will be applied in a post-print production step.

Using the Shape fixup it is easy to detect areas marked for glueing by special spot colored graphics objects, and create an opaque white shape above that area. The downside is that the glue markers will also be below that opaque white shape and thus will not be visible anymore. In order for the markers to become visible again, "Bring to front" can be used to move them above the opaque white shape.

The files used for this example can be downloaded below:

In the sample PDF, containing a label to be wrapped around a yoghurt cup, and glued where the ends of the label overlap, the striped green area indicates where no ink must be applied as glue will be put on this area. The spot color used for this striped green area has the name "Ink-free". Based on this, an opaque white area can be created that uses the same area, and thereafter, the then covered up striped green area can again be moved to the front.

In order to create an opaque white area, the "Create and apply shapes" fixup is used.

The shape (to be filled with opaque white) is derived from the rendered appearance of the green graphics objects (using the spot color "Ink-free").

The safest way to create an opaque white area is to use registration color (a special separation color named "All") at a percentage of 0%. By doing so, it does not even matter whether the white is set to overprint or knockout – it will knockout graphics objects on each and every plate (as long as it is above all other graphics objects).

Upon execution, the user is asked which spot color to look for (that is supposed to represent the ink-free area).

Once the fixup has been executed, a white area will appear on top of the "ink-free" area. Unfortunately none of the striped green graphics objects can be seen any longer, and without prior knowledge it would be hard to tell whether the area is white for design reasons or in order to keep it ink-free.

A good option to remedy this shortcoming, it is possible to bring the striped green objects in front of all other graphics objects again – by using the "Bring to front" fixup, as shown below:

Upon executing, the user will be asked for the spot color name used by the "ink- free" marker objects.

After the fixup has been executed, the striped green objects haven been moved in front of all other graphics objects, and have become visible again.

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