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4:3 aspect ratio and pixel aspect ratio
Why does a raw Super Nintendo capture look squeezed? Because CRT console pixels were not square. Enter the stored resolution and the system's pixel aspect ratio, and the calculator returns the corrected display, the one the 4:3 TV actually showed.
Historical PARs by system
| System | Stored | PAR | Corrected display | Final aspect ratio |
|---|---|---|---|---|
| NES / Famicom (NTSC) | 256×240 | 8:7 | 293×240 | 1.22 |
| Super Nintendo (NTSC) | 256×224 | 8:7 | 293×224 | 1.31 |
| Mega Drive H32 | 256×224 | 8:7 | 293×224 | 1.31 |
| Mega Drive H40 | 320×224 | 32:35 | 293×224 | 1.31 |
| Arcade Capcom CPS | 384×224 | 7:9 | 299×224 | 1.33 |
| Neo Geo | 320×224 | 14:15 | 299×224 | 1.33 |
| Game Boy Advance (LCD) | 240×160 | 1:1 | 240×160 | 1.5 |
Pixel aspect ratio is not display aspect ratio
The SNES generated 256×224 frames, and 256 divided by 224 is 8:7. But nobody played Super Mario World in 8:7: the tube TV stretched that signal until it filled the 4:3 screen. The math works once you separate two concepts. Display aspect ratio (DAR) is the shape of the final rectangle on screen. Pixel aspect ratio (PAR) is the shape of each individual pixel, and on classic consoles it was almost never square.
On the NES and SNES in NTSC, the 5.37 MHz pixel clock produces 8:7 pixels, wider than tall: the 256 stored pixels occupy the screen space of about 293 square ones. The Mega Drive lives in both worlds: in H32 mode (256 wide) it uses the same clock and the same 8:7; in H40 mode (320 wide) the clock rises to 6.71 MHz and pixels become narrow, 32:35. Look at the table: corrected 256×224 and corrected 320×224 produce the same ~293×224 image. That was the trick: different widths in memory, the same rectangle on the TV.
On Capcom arcades the effect is more dramatic: the CPS draws 384×224 and the 4:3 monitor squeezes it all, giving 7:9 pixels, much taller than wide. That is why a raw Street Fighter II capture looks too fat: the correction is missing. LCD handhelds such as the Game Boy Advance have physically square pixels (1:1), which is why on them what you see is exactly what sits in memory.
Emulating with correct PAR or with square pixels is the community holy war: sharp memory faithful 8:7, or TV faithful 4:3. There is no wrong answer, only a documented choice.
Sources: the NESdev wiki and forums (nesdev.org) for the NES and SNES 8:7; Sega technical communities (Sega-16, SegaXtreme) and PAR correcting emulation projects for the H40 32:35; shmups.system11.org forums and the discussions around Capcom's official collections for CPS at 4:3.
More CRT era tools: integer scaling calculator, ms to frames lag converter, cartridge megabit converter and console resolution archive. And if nostalgia strikes on another frequency, every pixel on these consoles was addressed in binary.
Last updated: · Methodology and sources