PDF backend configuration

You can configure Okular PDF rendering backend based on Poppler by choosing PDF from the list on the left part of the configuration dialog. The only configurable option is as follows.

Enhance thin lines

Drawing lines in Okular is implemented in two steps: generation of the clipping path and filling this clipping path. When the line in the original document is less than one pixel this two step implementation could cause problems. For those lines, the clipping path is filled with the filling color that depends on the thickness of the line part inside the clipping area. If the part of the line inside the clipping area gets very small the contrast between the shape and the background color can become too low for the line to be recognizable. The grids of such lines then looks very unpretty.

Thin line (red), its clipping path (dashed line) and pixel boundaries (black solid lines)Thin line shown at a low contrast

To enhance the look of the thin lines Okular implements two options.

The first option is Solid. With this option Okular adjusts clipping path and line position so that clipping path and line are on the same pixel boundary, i.e. Okular enlarges the thin lines to one pixel on the output device. This mode is similar to the Enhance thin lines in Adobe® Reader®. If this option is chosen, the thin lines are always enlarged.

Thin line with Solid enhancement

Thin line with Solid enhancement

The second option is Shape. With this option the clipping path and line are adjusted to pixel boundary as well, but the line intensity is corrected according to its width.

Thin line with Shape enhancement

Thin line with Shape enhancement

The thin lines are not enhanced by default (option No).