This is a really cool project and I am excited to build it and test it out on my CGA monitor. I am sure you have moved on from this to new pursuits, but can't help but ask a few things.
On the temporal dithering, one thing that I have noticed when doing that (on a Tandy and on tweaked CGA) is that if you take the resulting image and swap every other line you get a consistent brightness across both images and it helps flicker a lot. https://www.youtube.com/watch?v=MR1uq4y9G34 The picture is true to life, it doesn't flicker a lot. Certainly, it is there.
Have you thought about making the display 640x400 interlaced video? Not sure if 640x480 might work as well? Not sure how awful or full of flicker it will be, but would be neat. The ATI VGA Wonder will allow you to display 640x350 using some kind of process to get more colors on the monitor (and it does) but not sure if it is temporal or something else.
Last one, do you think you could overmodulate the signal to get more colors in 60 Hz? So, we have 16 levels of TTL, what if you were to drive the signal FASTER than the actual rate the pixel changed using PWM. So, if you are able to drive a 15.75 KHz signal and you could drive a signal at 4 times that at 63 KHz then I think during the pixel draw portion of the signal you could switch it faster than the raster scan and drive more than one color per pixel. At 4X you could drive Red-Black-Black-Black and probably get a darker red, or Blue, Blue, White, Red and get a light magenta. Odd combinations like Brown, Cyan, Red, Yellow would give even additional colors. I think the math works out to with 16 colors and 4 "cycles" per pixel you could get 3,876 combinations. If you could do 8 cycles per pixel that would require precision control of a 126 KHz signal that would give you 490,314 combinations. 12 "cycles" per pixel would be 17.4M colors which has to have every color close to 24 bit. 12 would require precision control of a 189 KHz signal. I don't know how the TTL to Analog RGB circuitry inside the 5153 would handle the frequency though or if it would switch fast enough. Anyway, if you read this far this is what your project made me think of.
Regardless, 640x400x17M colors on a TTL CGA monitor would be something to see for sure.
Hi,
This is a really cool project and I am excited to build it and test it out on my CGA monitor. I am sure you have moved on from this to new pursuits, but can't help but ask a few things.
Regardless, 640x400x17M colors on a TTL CGA monitor would be something to see for sure.