Blurry image with aspect ratio correction

Pogo{ · Post by **Pogo{** » Thu Jul 09, 2009 2:16 am

I noticed that using aspect ratio correction gave my games a slight blurred appearance. I didn't use scummvm for a while, but i couldn't recall this happening the last time i used it so i took a look at the source. With my extremely limited programming knowledge i managed to fix it by changing #define ASPECT_MODE kSlowAndPerfectAspectMode to kVeryFastAndUglyAspectMode in aspect.cpp

As this fix solved the issue for me this isn't really a problem, i'm just curious as to why the default behavior is to blur the image with what resembles a bilinear filter without any option to disable it. I'm pretty sure more people than me still got love for the raw pixels

. Hate to see them being stuck with the blur.

bobdevis · Post by **bobdevis** » Thu Jul 09, 2009 2:41 am

I have no info on this this problem/solution but this did make me curious.

Following common scene I would conclude that compensation for slightly non-square pixels in the original image would ALWAYS cause blur, unless you use a very specific large upscaler.

The compensation is smaller then one pixel, thus blurring HAS to occur.
If, of cause, the upscaler of the final image is a round multiple of one AND a round multiple of the aspect ration correction, THEN and only THEN can you compensate without any blurring.

fingolfin · Post by **fingolfin** » Thu Jul 09, 2009 7:30 am

Bobdevis has it spot on. In the end, kVeryFastAndUglyAspectMode does what it says: a fast and very ugly job. It duplicates some lines, which is very visible. So if you want a really "authentic" feeling, do not use aspect ratio correction, but rather play on a CRT, use fullscreen mode and adjust your CRT to the right ASR. Not possible with LCDs, of course, because they also would have to interpolate pixels.

Pogo{ · Post by **Pogo{** » Thu Jul 09, 2009 9:20 am

Ah, i just did quick comparisons and looked for blur so i didn't notice the line problems. I actually think i prefer them to the blur though

I do have a CRT, but it can't go above 75hz in non-4:3 resolutions which is too low for my poor eyes. Guess i'll have to hope for a revival of the opengl backend

Thanks alot for answering so quickly!

ps. I just noticed that i was mistaken about the default, it was actually kFastAndNiceAspectMode and not kSlowAndPerfectAspectMode. Now i sadly managed to break something in my compiler so i can't try, but would the "perfect" mode look slightly better?

fingolfin · Post by **fingolfin** » Thu Jul 09, 2009 4:37 pm

The perfect mode looks slightly better, yeah. But it still has to interpolate.

Just as OpenGL would have, hence you don't have to wait for a "revived" OpenGL port -- it wouldn't look different.