Converting VGA to component (RGB) video
Jon87
Posts: 14
Hi everyone. I've been having slight problems with dot crawl when displaying PAL video. I'm new to this but i did some research and found that its caused by interference between the chrominance and luminance.
With this in mind, i was wondering would it be possible to modify VGA_text.spin to pass appropriate values to VGA.spin to output component video (RGB) on the VGA port so i could connect to a television using something like this cable, connected to the demo board the demo board.
has this been done before? I haven't found any mention of component video after searching the forum. if it hasn't been tried, is there a reason? (there probably is
)
Cheers, Jon
With this in mind, i was wondering would it be possible to modify VGA_text.spin to pass appropriate values to VGA.spin to output component video (RGB) on the VGA port so i could connect to a television using something like this cable, connected to the demo board the demo board.
has this been done before? I haven't found any mention of component video after searching the forum. if it hasn't been tried, is there a reason? (there probably is
)Cheers, Jon
Comments
The S-video signal style works with PAL right? If so, why not just change VGFG to output chroma on start_pin+3? Most all existing TV graphics projects will work that way, the only real exception being Eric Ball's improved color code, which actually uses that pin as configured in the reference video circuit. The others just need a bit set to move the chroma to that pin. All that is needed is to disconnect pin 4 from the rest of the DAC, keeping the resistor in place. Wire up a cable, and enjoy separate chroma.
That said, I think component is great. The nice thing is that it's simple. One can output TV style frequencies with no worries, or crank the resolution up. If an analog device is used for display, most any resolution / timing combination is going to work. If it's low-def TV, one could choose PAL style 50Hz or NTSC style 60 Hz display output, depending on their need for blanking time. If it's a higher def device, then a progressive scan at TV frequencies would result in a great looking ~600 - 800 pixel x ~400 - 500 pixel display. Said output would work world wide, given a component capable device. The problem there is availability of them. Most HD devices do this, but an awful lot of ordinary definition devices don't, particularly in the States.
S-video, assuming it's available in PAL land (and it's gotta be, I'm sure I read that it is), is much more available, and at lower resolutions (~320 pixels), on par with what component would do anyway. Above that, it's still very good, and I think the PAL numbers are ~150 pixels or so higher, for the same quality statement.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Propeller Wiki: Share the coolness!
8x8 color 80 Column NTSC Text Object
Safety Tip: Life is as good as YOU think it is!
Post Edited (potatohead) : 4/13/2010 2:12:25 PM GMT
However the big question is sync. The first question is whether sync is separate (either H+V or separate H & V like VGA) or combined with one/all of the signals (typically Y or G). Again, the Propeller doesn't care, it just drives the signals. You also need to know whether sync is positive or negative (this goes for the video signals too).
But the real buggaboo is your TV probably expects an interlaced picture while the VGA driver does non-interlaced. So you'll probably need to create your own video driver which does interlaced video, but outputs VGA style.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Composite NTSC sprite driver: Forum
NTSC & PAL driver templates: ObEx Forum
OnePinTVText driver: ObEx Forum