CGX hardcopy dark shading

[mkraska]

In the example https://github.com/mkraska/CalculiX-Examples/tree/master/Drahtbiegen/Zug, file

https://github.com/mkraska/CalculiX-Examples/blob/master/Drahtbiegen/Zug/expansion.fbd

the second and the third hcpy png command produce different shades (second image is darker than on screen).

[mkraska]

dark shading can be mitigated by adding plots of some nodes in red (grey does not help) see example: https://github.com/mkraska/CalculiX-Examples/tree/master/Linear/ShearCenter

[mkraska]

Examples which exhibit the problem: https://github.com/mkraska/CalculiX-Examples/tree/master/RVE/PlanarSlide

[mkraska]

still persistent in 2.13.1