Gray test images

256 grays 80x80 cells (1280x1280 pixels)
256 grays 100x100 cells (1600x1600 pixels)
256 grays 120x120 cells (1920x1920 pixels)
256 grays 140x140 cells (2240x2240 pixels)
256 grays 160x160 cells (2560x2560 pixels)