16-bit vs. 32-bit rendering

The big issue here is 32 bits per pixel color. Why is it such a big deal? In a word, dithering. 16 bits per pixel is only enough to represent about 65,000 colors. While that's a lot, it's not enough to show seamless color gradients. Imagine a sample image which goes from blue at the top to green at the bottom. With 16bpp color, you will see a "stairstep" effect showing where each color stops and the next one begins. There simply are not enough color variations available to make each color blend into the next seamlessly. In order to lessen this effect, video cards use dithering to simulate more colors. They place small patterns of alternating color, typically in a checkerboard, to trick the eye into seeing an intermediate color.

Dithering tends to be more successful at higher resolutions. The pixels become small enough that they can't be readily distinguished, and the eye is more likely to be fooled into seeing that strip of alternating colors as an intermediate color instead of the mush of pixels that it really is. Different cards have different approaches to dithering, and some are more successful than others. One thing's certain, though: with 32 bits per pixel, you don't need to dither at all. You have so many colors-16.7 million, in fact-that the eye can no longer see the difference between one color and the next.

That's why the noticeable lack of dropoff in 16 and 32 bit resolution scores for the Rage 128 is exciting news. Normally, the additional bandwidth required for 32-bit is prohibitive. After all, 32 bits is double the information for every single pixel, for every single frame! The Rage 128 pulls off 32-bit color with only a minor performance penalty in Q2 and DethKarz, whereas the TNT suffers a noticeable dropoff at 800x600 and higher when switching to 32bpp. This indicates a superior memory architecture for the Rage128, and finally provides us with the ability to run at high color depths without loss of framerate.

Unfortunately, the excellent 32-bit performance comes at a price-our beta drivers have the worst 16-bit rendering I've seen since the bad old days of the Riva 128! According to ATI, this is primarily due to the beta drivers for the Rage128, but it's quite a disconcerting sight. The dithering method used leaves visible artifacts with heavy graininess and posterization. More on that later.