Anisotropic Filtering Quality

Now it’s time to compare in-game screenshots, and I’ve chosen Doom 3 because it’s an excellent test-bed due to its widespread shader, specular and texture aliasing. All of these screenshots are taken at 2560×1600, 16xAF and 8xMSAA. Note however the MSAA level won’t make any difference to the areas we’re looking at because they’re texture and/or shader aliasing.

Of interest here are the edges of the three vertical stripes inside the door because they’re affected by texture filtering. They sit to the left of the green monitor and are marked with white arrows

4850

285

5770

The 4850 clearly has the most jagged and wobbly edges of the three cards, especially the left-most line. The 5770 is basically equal to the GTX285, and this is a definite improvement that will be noticeable in-game during movement.

Now here’s another example that contains text:

4850

285

5770

The GTX285 has the sharpest text of the three, while the 4850 looks a tad blurrier, especially with the word “operations”. This is probably the angle of the text causing the difference with respect to ATi’s box filtering angles. The 5770 in contrast has much blurrier text than either card. This isn’t caused by the angle since we know the card’s AF is angle invariant, so my theory about the earlier “dead-zone” transfers into gaming to some degree.

My hypothesis is that in order to match nVidia’s lower levels of texture aliasing, ATi does it at the expense of texture clarity. This is similar to what we saw in the theoretical render, where the gray “dead-zone” didn’t have the same detail level on the 5770 as it did on the 4850/285.

So subjectively the 5770 will look better than the 4850 because it’ll have less aliasing, but some parts will be blurrier too. Overall nVidia’s filtering is still superior because it offers the sharpest text while being tied for the smoothest door at the same time. Remember, the goal of anisotropic filtering is to sharpen textures without introducing additional texture aliasing.