OSSC Classic: CGA Brown Fix
- This topic has 1 reply, 2 voices, and was last updated August 14, 2024 at 11:14 AM by
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Hi. It is possible to connect CGA/EGA cards to OSSC VGA input via a simple passive cable that has a few resistors on the RGB lines to bring them from TTL level to VGA voltage range.
I’ve built such cable and it works great with OSSC. The only issue is that this misses the “dark-yellow-must-become-brown” custom logic that is typically done in CGA/EGA monitors.. thus the picture looks slightly incorrect due to browns showing as yellow.
As you can see, the skin color of the characters has yellow edges. These should be brown.
On the OSSC side, I think all is needed is to implement a toggle (CGA Brown Fix) that triggers a comparator that detects when a pixel is within the dark-yellow color range, and replace it with brown. Adding such feature allows the OSSC to support CGA/EGA. Extra-points if the OSSC could detect the VSync’s signal level to automatically toggle-on/off the CGA brown fix, but honestly it’s not a very big deal.
For flexibility, it would be great if the OSSC menu could offer a range of intensities for the dark yellow color detection, as the exact value could be different from one cable to another (depending on resistor values used). That chosen intensity would also be applied on the replacement brown color in order to keep everything looking coherent.
Cheers!
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