I used to do it in circuits with CXA1645 or AD725.
But this question is not about soldering, it is about math and digital processing.
Imagine I am designing the entry-level graphics processor using FPGA, which outputs RGB using 5-bit DACs (currently considering R2R) with maximal resolution of 640*480, at 50 or 60 Hz.
The easiest and proven solution is attaching AD725 to the FPGA, and be happy with composite and S-video outputs.
However there's another possible way to consider - instead of feeding analog data to AD725 and let it play with this data, use FPGA's internal digital - precise and synced - data, to generate digital composite and S-video signals.
I can not come to conclusion if this is a good idea or not by browsing tons of resources on the internet, and have questions, asking for your experience and appraisal:
- Is it actually beneficial? I suspect NTSC/PAL composite (over standard RCA cable) may not be able to display 640*480 in proper way, even if math is done in digital and then converted to analog with dedicated DACs?
- RGB outputs are 5-bit, yielding 32768 colors. How wide composite DAC should be? Looking into nice pictures about IRE, color levels etc I am unable to even closely have an idea what it would be.
- Did you see related math anywhere to convert RGB to composite (as I understand target is called HCL)? I have seen it is required to convert to XYZ first, and only then to HCL...
- Pictures like this look cool, is there an explanation for dummies? While I can get how sync and luma work, I have difficulties with hue and chroma, and how to make them from RGB data.
I suspect all these may require lots of background, will be very happy for references to the texbooks to get it.