(This thread is somewhat in jest, I needed my own accuracy thread)
After seeing the NTSC borders thread, I thought I'd bring this up: I don't think anybody is using the correct pixel-aspect ratio.
I have determined the square pixel scaling to be 293 x 240. Originally I thought it was 292, which I see has been proposed in another thread, but I came to that conclusion assuming a TV could adaptively vary the speed/horizontal width based on line timing in order to keep active video centered at different line frequencies. After diving deeper into TV circuits I see that they cannot, the angle of integration on the deflection sweep is fixed which means that NES video still sweeps at the same speed as standard NTSC video.
The justification is that TVs are calibrated for a 4:3 aspect with 52 + 59/90 us of active video by 486 lines which is the most agreed upon historical line count.
486 * (4/3) makes a square pixel resolution of 648 x 486. Since we're dealing with progressive video it's technically 324 x 243. The 3 missing vertical lines are irrelevant since they don't affect the pixel aspect.
The NES' active video period is 47.678306878306878306878306894438 us
(47.678306878306878306878306894438 us) / (52 + 59/90 us) * 324 = 293.37400898320923642721490378595 square pixels to active NES video, which leads to a pixel aspect of ~1.146. The aspect ratio is 293.374:240, or ~1.222.
Despite practically all of the border pixels (and a slight amount of front porch) falling into the active video area, if you emulate the 26 border pixels, do note that they cannot fit into 320, 640 etc. fixed square pixel screens without reducing the vertical resolution. You will have to drop 3.1698 of them. That is, unless you emulate a display calibrated to 480 lines in which case you can scale the 282 border and active pixels directly to your horizontal resolution (in a 4:3 aspect) because it will fall within 1 pixel tolerance, pretty cool. A "480" calibrated display will scale 256 NES pixels to ~290 square pixels. (320 / approx. 282 * 256)
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Don't hold me to this because it's been a long time since I looked at the 2A03 layout, but from memory, something else I haven't seen documented is that the DMC DAC's two least significant bits carry the same weight, which perhaps could explain the mixer "non-linearities".
After seeing the NTSC borders thread, I thought I'd bring this up: I don't think anybody is using the correct pixel-aspect ratio.
I have determined the square pixel scaling to be 293 x 240. Originally I thought it was 292, which I see has been proposed in another thread, but I came to that conclusion assuming a TV could adaptively vary the speed/horizontal width based on line timing in order to keep active video centered at different line frequencies. After diving deeper into TV circuits I see that they cannot, the angle of integration on the deflection sweep is fixed which means that NES video still sweeps at the same speed as standard NTSC video.
The justification is that TVs are calibrated for a 4:3 aspect with 52 + 59/90 us of active video by 486 lines which is the most agreed upon historical line count.
486 * (4/3) makes a square pixel resolution of 648 x 486. Since we're dealing with progressive video it's technically 324 x 243. The 3 missing vertical lines are irrelevant since they don't affect the pixel aspect.
The NES' active video period is 47.678306878306878306878306894438 us
(47.678306878306878306878306894438 us) / (52 + 59/90 us) * 324 = 293.37400898320923642721490378595 square pixels to active NES video, which leads to a pixel aspect of ~1.146. The aspect ratio is 293.374:240, or ~1.222.
Despite practically all of the border pixels (and a slight amount of front porch) falling into the active video area, if you emulate the 26 border pixels, do note that they cannot fit into 320, 640 etc. fixed square pixel screens without reducing the vertical resolution. You will have to drop 3.1698 of them. That is, unless you emulate a display calibrated to 480 lines in which case you can scale the 282 border and active pixels directly to your horizontal resolution (in a 4:3 aspect) because it will fall within 1 pixel tolerance, pretty cool. A "480" calibrated display will scale 256 NES pixels to ~290 square pixels. (320 / approx. 282 * 256)
-----
Don't hold me to this because it's been a long time since I looked at the 2A03 layout, but from memory, something else I haven't seen documented is that the DMC DAC's two least significant bits carry the same weight, which perhaps could explain the mixer "non-linearities".