Basically to whichever games use VGA's Mode 13h (320×200 in 256 colors). It stretches the graphics to conform to the standard aspect ratio (4:3) at that time for monitors. On modern graphic modes if you run DosBox windowed you might noticed that some games look a bit "flat", that's because Mode 13h didn't use square pixels like the rest of the VGA modes (ex. 640×480 in 16 colors) or the later SVGA.

Ex:
vs

The first one uses aspect ratio correction, the other doesn't.

Using DOSBox with a real CRT and fullresolution=original.

One situation is tweaked mode 13h at 320x240 resolution, which has a 1:1 aspect. DOSBox slightly miscalculates its pixel aspect ratio as 0.99 instead of 1.00, which typically causes a slightly blurred appearance with aspect=true that you can avoid with aspect=false, and correction isn't needed with a 1:1 aspect, anyway.

ripsaw8080 wrote:

One situation is tweaked mode 13h at 320x240 resolution, which has a 1:1 aspect. DOSBox slightly miscalculates its pixel aspect ratio as 0.99 instead of 1.00, which typically causes a slightly blurred appearance with aspect=true that you can avoid with aspect=false, and correction isn't needed with a 1:1 aspect, anyway.

Any other way to fix this mode's wide appearance? The blurriness also bothers me.

marooned_on_mars wrote:

Any other way to fix this mode's wide appearance? The blurriness also bothers me.

I think you're referring to normal (not tweaked) mode 13h at 320x200, which does need correction if you want proper aspect. You can try output=openglnb which uses irregular sized pixel blocks instead of blurring, but FYI both the blurring and irregular blocks are less noticeable when there are more pixels to work with, such as in fullscreen mode (or windowed mode with "scaler=normal3x")

Ugh, irregular pixel blocks. I could try a large scaler but my monitor is crap and I can't even use x3 scaler X.X

Well, you can try setting the highest fullresolution= and windowresolution= you can manage coupled with output=openglnb, scaler=none, aspect=true. I think that gives pretty good results with windowresolution=1280x960. The more vertical pixels you give it to work with, the less noticeable the aspect correction artifacts will be.

The best way is to display the output using the normal2x filter on a CRT display and use your vertical and horizontal size and position adjustments to make your output indistinguishable from a real vintage PC.

Well in that case I'd just switch to full screen, since I have a CRT and my graphics card is able to use the native VGA modes it displays properly. The only problem is that I can't use the fullscreen mode since most of the time I need to see the console window. 😒

ripsaw8080 wrote:

One situation is tweaked mode 13h at 320x240 resolution, which has a 1:1 aspect. DOSBox slightly miscalculates its pixel aspect ratio as 0.99 instead of 1.00, which typically causes a slightly blurred appearance with aspect=true that you can avoid with aspect=false, and correction isn't needed with a 1:1 aspect, anyway.

We do ? Sounds like worth fixing.

@Qbix: Another one: Aspect correction error?.

Qbix wrote:

ripsaw8080 wrote:

One situation is tweaked mode 13h at 320x240 resolution, which has a 1:1 aspect. DOSBox slightly miscalculates its pixel aspect ratio as 0.99 instead of 1.00, which typically causes a slightly blurred appearance with aspect=true that you can avoid with aspect=false, and correction isn't needed with a 1:1 aspect, anyway.

We do ? Sounds like worth fixing.

See here for my report of the issue. Hal suggested rounding off. ;)

leileilol wrote:

Using DOSBox with a real CRT and fullresolution=original.

The best way is to display the output using the normal2x filter on a CRT display and use your vertical and horizontal size and position adjustments to make your output indistinguishable from a real vintage PC.

This would be ideal, but my CRT is in storage and I don't have room to play with it on my desk anyway... for now I can only dream. But someday!

Basically to whichever games use VGA's Mode 13h (320×200 in 256 colors). It stretches the graphics to conform to the standard aspect ratio (4:3) at that time for monitors. On modern graphic modes if you run DosBox windowed you might noticed that some games look a bit "flat", that's because Mode 13h didn't use square pixels like the rest of the VGA modes (ex. 640×480 in 16 colors) or the later SVGA.

But is this an unbending rule? I seem to recall discussions that there are 320x200 games which nevertheless are meant to be displayed as if they had square pixels. For example Sierra games are 320x200 but look best with aspect=true, right? What I have been doing is playing in a 1280x960 fullscreen with aspect=true.