The multiplexing finally works! The Matrix can now show images saved in RAM. Per pixel 8 Bit are used (RRRGGGBB). Here is a image of the result:

photographing this is not easy because of the multiplexing. This can be also seen in this image by the different brightness of the lines. But the human eye is worse then this camera. So you do not see it.

The image "file" for that looks like this (I used some defines for the color values):

{ {WHITE, YELLOW, CYAN, GREEN, PINK, RED, BLUE, BLACK, ...},
  {WHITE, YELLOW, CYAN, GREEN, PINK, RED, BLUE, BLACK, ...},
  {WHITE, YELLOW, CYAN, GREEN, PINK, RED, BLUE, BLACK, ...},
  {WHITE, YELLOW, CYAN, GREEN, PINK, RED, BLUE, BLACK, ...},
...};

compared to the file extract, the display is rotated by 180° on the image. I should really mark the upper right corner somehow to make the images right orientated.