MajorMar wrote: ↑
Fri Oct 30, 2020 7:15 am
I can do if you still want them. However, I found that increasing the sampling phase from 0 to 1 fixed the issue. Here is a video of what I was seeing. It seems the default config for PC has sampling phase set to 0. Perhaps I am masking the real problem by doing this. Not sure.
Thanks for the video. That sort of wavy lines effect is expected when the sample phase is set to the worst possible value for a source as it is sampling on the edge of each pixel rather than the centre of each pixel so the results are messed up by pixel transitions.
I think I know what the problem is:
It looks like the text mode pixels have a 180 degree phase difference to the graphics mode pixels which means that the best possible sampling phase for text is the worst possible value for graphics and vice-versa. This doesn't happen with my CGA sources so it's probably a peculiarity of the original IBM CGA card.
You may find that the best value for graphics is around 2 or 3 and the best value for text is 5 or 0 with the x6 multiplier.
Try running an auto calibration in text mode followed by another in graphics mode and then save and post the log. Note the graphics will have to be stationary when running the calibration
To work around this, the sampling phase should be set to a value half way between the best values for text and graphics and that's what you are doing by adjusting the sampling phase to 1. However with the x6 multiplier there are only 6 sampling phase values and that isn't a fine enough resolution to get a good intermediate value.
You can change the multiplier to x8 and that will increase the sampling phase range to 8 and that might be enough for a clean result in both text and graphics so try that and then manually adjust the sampling phase value for best quality in both text and graphics.
I'm currently working on the next firmware release and I think I will add some additional multiplier options like x10 or x12 which should then give a much more reliable result as there will be many more points to try in between the two optimal values.
I recall there are two different designs of the IBM CGA card and they have different NTSC artifact colours which indicates they have different pixel phases so maybe this problem only affects one of the versions.
BTW That log indicates you are using a 1440 x 900 monitor which can't use integer scaling as there aren't enough pixels vertically so it has to fall back to using interpolated scaling. You will get the best/sharpest results with CGA / EGA using either 1920x1080, 1920x1200, 1680x1050 or 1600x1200 monitors.