Creating pixel art

the brightest colors of the brown ramps look like the yellow group
the second color is orange group vs red group

the two yellows are very little different
subtle slides within a group are possible and then there are dead zones between the groups
the category I mean is the nanometers

I’ve been wondering what the exact MSX pixel aspect ratios (PAR) are. This is relevant when drawing graphics on PC since they have square (1:1) pixels while the MSX doesn’t.

The V9938 vertical display area at 60 Hz is 243 lines, at 50 Hz it is 294 lines. The horizontal display area including borders is 1139 cycles, or 284,75 pixels (/4) in screen modes other than 3, 6 and 7.

As far as I know the display aspect ratio (DAR) of a TV is calculated based on the full frame output including overscan (borders), so we can derive the pixel aspect ratios from these numbers.

The pixel aspect ratios on a 4:3 display are (4y / 3x):

60 Hz: 1296 / 1139 = 1,138 = ~9:8
50 Hz: 1568 / 1139 = 1,377 = ~7:5

The pixel aspect ratios on a 16:9 display are (16y / 9x):

60 Hz: 1728 / 1139 = 1,517 = ~3:2
50 Hz: 6272 / 3417 = 1,836 = ~11:6

In openMSX these would correspond to horizontal_stretch values of 281 (60 Hz 4:3), 232 (50 Hz 4:3), 211 (60 Hz 16:9) and 174 (50 Hz 16:9). Unfortunately only one of these can actually be entered because the values can not be <256. The default is 280 though, so quite correct for a 60 Hz MSX.

None of the MSX video chips were ever targeted for 16:9 displays. Why even take it into account?

Get with the times, Manuel! Bigger screen. No letterbox. Most people’s TVs are widescreen. I’m entertaining the thought, might be nice for something. For 3D it’d be an easy projection matrix change. If someone makes a widescreen game, I will be the last to protest. I think it’d be fun.

(Not saying that I’m going to make 16:9 content, but to say “why even take it into account”… it’s not a ridiculous idea. Either way if I’m going to list aspect ratios, I think it makes sense to also list them for the most ubiquitous display aspect ratio out there nowadays.)

the aspect ratio is an ungoogleable topic. in a old book about analog TV I found:
585 of 625 lines
52 us of 64 us
that is the maximum display area, the rest of the time is sync

calculating the MSX pixels:
the MSX has 342 pixels per line.
52/64 * 342 pixels = 277,8 pixels in TV display area
585 lines / 2 = 292,5 lines in a 20ms frame
277,8 * w / 292,5 = 4 : 3
w = 4 / 3 / 277,8 * 292,5 = 1,403 PAL MSX aspect ratio

a sighting: the 75P manual of CIRCLE too says 1.4

if one would take 64us, 625 lines to calculate it then one would end up with a different ratio!
the total timings have a different ratio than the display area
because horizontal blank is more problematic and so snips more percent off the usable display