The HDMI output on your graphic card might be set to Limited (16-235) color range. I changed the HDMI setting (Nvidia 1060) to my Samsung computer monitor to Full 0-255 and I think it has made a slight difference to the black and white areas. If you are using a large HDTV (not a computer monitor) it might not make a difference. I think that no matter the resolution slideshows created by a video editing program  (that creates YUV 16-235) will never be as good as a PTE .exe RGB 0-255 slideshows (p