From the images and demo videos, it is obvious that the video quality is barely acceptable. There are two main problems:

• image sharpness - there is cross-bleeding of colors, noise artifacts etc.
• color resolution - only 8 basic colors are supported

Solutions for image sharpness

The flash A/D as I prototyped is very much a "chewing gum/duct-tape" solution, that can be improved in many ways:

• Put the circuit on a permanent solder board
• Keep wiring trimmed and matched
• Use higher quality potentiometers that allow finer and more stable regulation of threshold voltage
• Introduce external 21.47727MHz crystal to drive the sampler circuit instead of multiplying CPUCLK (which is XTAL/6) by 6 on FPGA

Solutions for color resolution

With 1-bit flash A/D per color channel only following colors can be supported:

For a small improvement of resolution, for example from 1 to 2 bits, additional LM339 comparator per color channel could be used. However using 6 LM339s instead of 3 would not double the color resolution. Reason is that 2 LM339 set at 1/3 and 2/3 thresholds would produce 3 valid combinations:

Still, 6-bit color digital vector obtained like this could be simply mapped at least to a valid 16-color table.

One additional interesting experiment would be to use the popular LM3914 dot-bar driver chip as a flash A/D. Theoretically, full 3-bit A/D conversion could be obtained from its 10 stage outputs.