A person on the Beyond3D forums tested various games, and found that some 360 games don't even run at 720p, and are instead upscaled to it. Halo 3 and Perfect Dark Zero, for example, run at 640p, while PGR3 and Tomb Raider run at a measly 600p.

It has also been noted that it runs at 1138x640 with only Bilinear filtering, no Anti Aliasing, and gets roughly 30 frames per second average.

To quote gamerwar who explains the math behind the calculations:

quote

Each “step” in a jaggy alias line equals one vertical pixel at the images native resolution (for angles beneath 45 degrees). In this example there are 16 steps in the jagged line. This means in the native rendering, there in a 16 pixel height difference between step 1, and step 16. This picture was taken on a 720p native LCD, running Halo 3 at “720p.” So when you have an alias line with 16 steps, there should be a physical height difference of 16 pixels. But instead here, there is an 18 pixel height difference!

What this means is the native image is only 16/18, or 88.88% (repeating), of the 720p outputted image. That means Halo 3 is only internally rendered at 640p, and the image is upscaled by the 360 to 1280×720.

Running at only 1138×640, that means there are 728,320 pixels. That’s a full 193,280 pixels LESS than 720p. In fact, it is even less pixels than your very average 1024×768! Hardly what anyone would consider “high-def.”

I tested approximately sixty X360 games (and lot of PS3 games too ), all are 720p except two 1080p (VT3 and NBA street), two 600p (PGR3 and Tomb Raider) and Two 640p (Perfect Dark and Halo3).

Guticb via forum.beyond3d.com »