Anti-Aliasing on LCD

[userofcomputer]

As far as I understand, Anti-Aliasing smooth out the jaggies by increasing the resolution in that particular spot?

But if this is correct, how can AA work on LCDs which have a native res?

(Maybe should've been posted in Technical?)

 

[xtknight]

Anti-aliasing doesn't actually modify the viewport's size or density at all. The matrix of the screen remains the same. Supersampling renders the object at a double (2xAA) resolution, and then it takes the average of a block of four pixels to form one at the lower res that it's running at. This results in the illusion of a higher resolution at a lower actual size. And also lines appear smoother because of this. Pixels adjacent to the object have been "gradually" blended in and the effect of sudden sharpness is reduced resulting in a smoother image.

Supersampling does this to the whole screen (geometry+textures), and multisampling does this for geometry.

There's also font antialiasing. Subpixel font rendering like ClearType takes advantage of the sharpness of LCDs and uses the subpixels to blend the font better in with the background resulting in smoother fonts. CRTs basically already do this just due to the way they work and generally it's best you keep ClearType off for them, unless you have an unusually sharp CRT. Likewise LCDs may look unusually sharp unless you use anti-aliasing. That goes for both images and fonts.

 

[darkswordsman17]

I'm sure someone who knows it better can explain it better, but I'll give it a try.

Anti-Aliasing does one of two things. I will focus on FSAA (Full Screen AA) as its a little easier for me to explain. Say you're running at 1600x1200 and you're using 2xAA in a game. What the video card does is take the full resolution and then doubles it, effectively rendering a 3200x2400 pixel image, and then downconverts it back to the original resolution, 1600x1200 in this case.

So, the reason why AA works is that its not changing the resolution the game is running at, it just renders the image at the resolution dictated by what level of AA you choose, and then downsamples it back to the original resolution, the key being that last part (downsampling).

 

[Cobolman]

Naw, Anti-Aliasing has nothing to do with resolution.

It's a bit difficult to explain without pictures, but I'll give it a shot.

Say you have a picture, which is half blue and half red, and the separation is a diagonal line. Pixels are a grid, so instead of a smooth line, you end up with jaggies.

Like so:

bbbrrr
bbbrrr
bbrrrr
bbrrrr

With anti-aliasing, you change the color of pixels near the jaggy spot, by mixing the two colors. With red and blue, this would be purple. This fools your eye into thinking it's a smooth line.

bbbrrr
bbPrrr
bbrrrr
bbrrrr

Think of it as smudging, but only in jaggy spots.

 

[userofcomputer]

So eg if there's a black wire going through the air and I apply AA, it makes so that the pixels around the wire that before was part of the sky, now slowly changes color from blue to black so that there isn't any sharp edge?

Edit: Cobolman said exactly this, had to edit so I wouldn't look like a fool... Well thanks for clearing this out.

 

[Cobolman]

Exactly.

 

[userofcomputer]

While we're at it, maybe someone could quickly explain Anisotropic Filtering too?

 

[Markbnj]

http://en.wikipedia.org/wiki/Anisotropic_filtering