TV safe area

[Chilly Willy]

I used a JROK RGB to Component converter, and is even powered by the 5v the AV connector outputs.

I was about to ask how you got component output on your Genesis.

A scan doubler would be nice - then I could play my SEGA on a regular LCD monitor. Hmm... they make scan doublers for the Amiga. I should see what's still available.

[evildragon]

Noticed something.

When in 320x224, screen is centered perfectly for me. (NTSC system)

When in 256x224, it shifts slightly to the left.

[Eke]

For proper aspect, I'd recommend using a 352x240/288 buffer for H40 modes, and letting the GC scale to 640x480 (you'll see the border, but since the GC does overscan by default that is likely to be hidden). Render your Genesis display to the center 320x224/240 of said buffer (most released games used 224 line mode so that's not likely to be a major problem). Unused pixels in the "border" should be set to the color pointed to by VDP register $07, and this should be done on a line-by-line basis (since changing $07 mid-screen does change the border color too).

I'm not 100% sure of what the equivalent buffer should be for H32 modes - 352/320=1.1*256=281.6 which I'd round to 282, so try 282x240/288.

I made some progress recently (both horizontal & vertical borders are correctly emulated, line by line, and the interlaced 2 mode now looks far better), which was not really difficult but I still have some doubts about the correct aspect ratio to use when scaling the resulting buffer to the TV screen.

What's confusing me is pixel aspect ratio: does the fact that the 320x224 image is designed to fit a full 4:3 TV screen means that 320:224 (10:7) is the original aspect ratio ?

I would rather thought that the correct aspect ratio is 352:240 (or whatever number it is, seems more like 350 or 348) and that the 320x224 active display appears "fullscreen" on TV only because vertical and horizontal overscan amount are not the same. Is that correct ?

[TmEE co.(TM)]

On NTSC, you have non-square pixels... square pixels are only in PAL. And if you want to really emulate things correctly, then when you set 240line res in NTSC, you should make screen scrolling, and VBLs happen at 30Hz.

[evildragon]

That makes no sense, because NTSC can handle 240 lines, i mean it is called 240p... That means the Genesis can't output it correctly.

[Chilly Willy]

That makes no sense, because NTSC can handle 240 lines, i mean it is called 240p... That means the Genesis can't output it correctly.

Yeah, the engineers probably only expect people to set 240 mode for PAL, so they do PAL stuff even though the Genny is still in NTSC mode.

[evildragon]

That makes no sense, because NTSC can handle 240 lines, i mean it is called 240p... That means the Genesis can't output it correctly.

Yeah, the engineers probably only expect people to set 240 mode for PAL, so they do PAL stuff even though the Genny is still in NTSC mode.

I wonder if adjusting vertical hold would actually result in a 240 line picture in 60Hz mode.

[Chilly Willy]

That makes no sense, because NTSC can handle 240 lines, i mean it is called 240p... That means the Genesis can't output it correctly.

Yeah, the engineers probably only expect people to set 240 mode for PAL, so they do PAL stuff even though the Genny is still in NTSC mode.

I wonder if adjusting vertical hold would actually result in a 240 line picture in 60Hz mode.

Or a better TV.

[evildragon]

Yeah, the engineers probably only expect people to set 240 mode for PAL, so they do PAL stuff even though the Genny is still in NTSC mode.

I wonder if adjusting vertical hold would actually result in a 240 line picture in 60Hz mode.

Or a better TV.

Nah, a better Genesis VDP would be great though.

Most TV's have a fixed V-Hold, and better ones have the V-Hold fixed between 50 and 60Hz.

Mine is HDTV CRT, and has a fixed 60Hz V-Hold. Anything 50Hz gets resampled to 60Hz and looks like shit though.

[Chilly Willy]

The 1084 my Genesis is hooked to can take anything from about 45 Hz to 80 Hz. I'd try it but I'd need a CD version as I don't have a flash cart.

[TmEE co.(TM)]

It's MDs VDP that does the rolling and incorrect refresh when in 240 and NTSC.

[evildragon]

It's MDs VDP that does the rolling and incorrect refresh when in 240 and NTSC.

That's why I said: "Nah, a better Genesis VDP would be great though."

[TmEE co.(TM)]

And actually waht use would you have for 320x240 if don't see lots of pixels vertically... 240 just adds more of them (but its not the case on new TVs).

[Eke]

I have no idea about how to simulate a "rolling screen" so I guess I would leave this unemulated for the moment

ANyway, about the aspect raio: I just realized that the right number of "active" lines (including borders) ouputed by the VDP is 243 lines in NTSC, not 240. (288 in PAL)

And that 320:224 is equivalent to 347:243 so maybe this is indeed the correct ratio to use when emulating borders and scaling the rendered display to 640x480.

Btw, has anybody captured the video signal from a PAL genesis as you did here for the NTSC one ? I wonder if the horizontal border widths are the same (i.e the total number of "active" pixels is the same)

[Eke]

full overscan emulation in action

http://www.youtube.com/watch?v=SmNMhd0msF0

what make me smile and reminded me of this topic is the first comment "Those blue bars are super ugly"

accuracy forever