Gamecube 480p 2x mode aspect ratio not 4:3. Any ideas?
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Sorry to unearth this but wanted to add some points, since resolutions on this generation seems to always be an issue.
First, the behavior of displays at this time was different. So, both EDTV CRTs and later SD/HD/EDTV compatible LCDs that had multiple digital and analog inputs understood mostly what was going on with the signal.
People get very confused with Dreamcast’s VGA output, thinking it is VESA, it is not. It is an EDTV resolution carrying 480p TV signal over VGA to TVs, not monitors. This is why the picture has an active area of 720 vertical “pixels”, minus overscan to 704 that is also mentioned many times. These are 10:11 skinny pixels that must be scaled by that factor to match the square pixels on LCDs – this will equal 4:3 640×480 resolution.
Now, I won’t go into the PS2 but Xbox and Gamecube have the same output but on the more modern component cables. Xbox is interesting because with softmods one can test the output res:
- 480i -> 640×480
- 576i -> 640×576
- 480p -> 720×480 (3:2)
- 720p is HDTV, so nothing wierd there.
Now, if you notice 480p is not what most people would expect for 4:3 resolutions, as it is 3:2 instead. This is the same as Dreamcast, as it is EDTV. AFAIK there is no “HDTV” 480p mode at this time, just EDTV. On EDTV, digital signals are encoded over analog and use the signal’s 704 skinny “pixels” that must then be scaled to match 640×480 output.
So, one can display this EDTV 480p on CRTs, they will usually auto scan and fit the image. No problema, Dreamcast is the same, even though the monitor is expecting VESA, it can adjust on the fly.
TVs knew to scale horizontally and others have an option you can set. On my old LG LCD, with this Xbox 480p it will not allow the option “just scan”, even though it works fine on 480i. It needs you tell if it is a 4:3 or 16:9, which will display everything correctly. (component or converted to HDMI works).
If you plug into an LCD monitor, most often they will have “aspect ratio scale” or “fill”. Some have 16:9 or 4:3 options. You can come across monitors that will interpret aspect ratio as with square pixels! So a 720×480 image will display in 3:2 and be in between 16:9 and 4:3, so not good.
On the Xbox the issue is mostly that if you don’t want to use anamorphic widescreen for clarity, this way you can’t display proper 4:3 without some kind of OSSC device.
Output vs Render Resolution
So: Gamecubes that have 3 modes? Well, this 448 vertical or even 512×448 modes are render resolutions and unrelated to A.R. or output. This is probably related to extra performance and overscan on the vertical axis, which is not something in the spec. This is what I say these are “render” resolutions.
Those are supposed to be scaled before output, except for the vertical axis on 480i sources – 512 horizontal has to be scaled. What you want on your display is always 4:3! This is 640×480 display resolution, which on an analog encoded, digital signal will be 704×480 with the 8px horizontal margins discarded.
If you skip the internal scaler, you will need to do scaling somewhere, like the 3 modes mentioned above. It is scaling once, then another downscale at the display but it is need. Usually flicker and softning filters do worse things to picture quality on interlaced signals.
I you look through Dolphin emulator code, you will notice there are codepaths to scale the image to the correct aspect ratio. Fortunately, one can scale the render res before this step, so the loss of detail from scaling 10:11 pixels is smaller. PS2 is the same and many games render at 512×448.
This is why this also happens on Xbox and Dreamcast. PS2 has less support for EDTV, so I’m not sure about the details.
Interlaced signals
On full analog sources, there is no wierd pixel issues. Resolution is 640×480, as expected and TVs know (or can be adjusted) to fit the horizontal area on the screen. I find that Xbox component at 480i, with filters disabled, seems to have quite good quality, despite vertical resolution loss.
This may be due to the TV conversion being quite good and it was with a still image though.
But there are the usual caveats with this:
- Lag or interlacing flicker, other interlacing artifacts need to be addressed.
- Xbox Conexant encoder seems to add noise at 480i
- Wii has bugs in earlier years related to the encoder messing the output. This can be fixed on software now.
- Need to disable flicker and soften filters in software, where supported.
As has become norm, getting the signal before the scaler and then doing the 4:3 or 16:9 anamorphic conversion where needed, would be the best display quality. This will skip DAC and ADC that push video into and out of 704×480 signal resolutions.
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