Started by radorn, August 11, 2017, 11:23:38 AM
Quote from: radorn on August 11, 2017, 11:23:38 AMHey, waiter! There's some chroma in my luma!The most annoying outcome of this is that I get this dot-crawl like interference all over the screen instead of just the edges where composite normally fails to separate chroma from luma. But since SVideo is supposed to have them already separate, the luma channel just takes the chroma dots as part of the picture.I use a Bt878 PCI capture card combined with DScaler. Poking arround I found this special input mode that expects a composite signal over the luma pin of the SVideo connector.These pictures were taken from a PAL N64 that was locked up by yanking the cartridge. The point was to be able to take several shot of the exact same image using different settings on the capture card.Here are the results:rom_EUR - hw_NUS-001(EUR) - output_SVIDEO - input_COMPOSITE-OVER-SVIDEO - format_PAL50 - LumaAGC_OFFIt's almost grayscale, but there's a faint hint of color...rom_EUR - hw_NUS-001(EUR) - output_SVIDEO - input_COMPOSITE-OVER-SVIDEO - format_PAL50 - LumaAGC_ONNow with chroma AGC enabled, we get colors, although the picture quality is garbage.I got this kind of shitty picture when I tried to feed S-Video to a PAL TV with a single SCART input. Obviously it didn't support SVIDEO at all. Now I understand why I got that kind of picture. There was a faint chroma shadow in the luma pin and the AGC circuit was amplifying it to normal levels, with results even worse than seen here.Nevertheless, notice how there's no all-over-dotcrawl like in the pictures below. This is because decoding it as composite kicks in the chroma separation circuitry.rom_EUR - hw_NUS-001(EUR) - output_SVIDEO - input_SVIDEO - decoded_PAL50 - ChromaAGC_OFFNow the picture looks normal, albeit with the chroma signal causing dot patterning all over the place.rom_EUR - hw_NUS-001(EUR) - output_SVIDEO - input_SVIDEO - decoded_PAL50 - Chroma_AGC_ONhere I activated chroma AGC, but it seems to blow up the colors a bit too much. I don't have an RGB picture to compare to, but it seems too saturated to me.Anyway. The question is simple: Who's put chroma in my luma? Does it come out like that from the DAC? some other components between the DAC and the AV multiout? Is the cable to blame (bad shielding)? Some other possible culprit?I'm assuming there's also some luma in my chroma, possibly affecting color decoding too, but the chroma-in-luma issue seems way more noticeable.