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NVIDIA GeForce 7800 GTX (G70)

By Vijay Anand - 22 Jun 2005

NVIDIA Intellisample 4.0 Engine

Intellisample Basics

The Intellisample engine is also upgraded to the fourth iteration and it builds upon the third generation found in the GeForce 6 series. We strongly suggest reading up our NV40 Preview article to get yourself acquainted if you haven't a clue on it. For summary's sake, the Intellisample engine is all about NVIDIA's full scene antialiasing (FSAA), anisotropic filtering (AF) and high-resolution compression technology that condenses color, texture and z-data.


Intellisample 3.0 (NV40)

Intellisample 3.0 in the GeForce 6 series furthered the basic Intellisample engine by implementing the rotated grid antialiasing, 16x AF and 64-bit texture filtering and blending. The last feature enables photorealistic lighting and shadow effects by means of representing data in 64-bit floating-point format. This means 16-bits are allocated for each of the primary color channels (R, G, B) and an alpha channel. Just to stray off here for a bit, the alpha channel, like in Photoshop, is used to create transparency effects (fog, glass, mist, etc.) with the primary channels when blended together. Where once upon a time the industry represented the entire color spectrum in just 16-bits, the 64-bit floating-point format allows 16-bits allocated to each color channel, greatly increasing the color spectrum for accurate reproduction. This is what High Dynamic Range (HDR) image reproduction is all about as it's able to replicate the extreme dark and extreme bright values accurately, which might have otherwise been compressed when using the current standard 32-bit RGB pixel color format (8-bit integer for each component).


Intellisample 4.0 (G70)

Intellisample version 4.0 in the G70 architecture builds upon Intellisample 3.0 by improving rotated grid antialiasing performance, supports normal map compression and a new antialiasing mode - Transparency adaptive supersampling and Transparency adaptive multisampling. Let's tackle all these features one at a time.


Intellisample 4.0 - Normal Map Compression

Improved rotated grid antialiasing performance is purely internal tweaking by NVIDIA for better high-resolution antialiasing throughput. Normal map compression is however a new feature to the G70 architecture. First initiated by ATI via its 3Dc feature (which is normal map compression using a FOURCC texture compression format), we've discussed why it came about and how it aids games in this article here . It was available on all of ATI's RADEON X850/800/700 series, but wasn't available on the competing GeForce 6 series in any equivalent form. Looks like developers did like ATI's 3Dc (including the folks at NVIDIA) that the new G70 was designed to incorporate an equivalently competent normal map compression technique.

NVIDIA uses a different texture compression format, choosing to go with the V8U8 algorithm, but they've revealed to us that there's no cause of compatibility if a game should use ATI's 3Dc. NVIDIA's driver transparently converts ATI's 3Dc maps, if encountered, into the V8U8 format for it's hardware's use. So although there's an extra step involved in the process, the compatibility is kept intact and neither developers nor the consumers should have concerns with regards to game quality being compromised. What we do wonder is if ATI's hardware can do likewise to accept the format used by NVIDIA should games choose to use that. We'll find that out in due time and update you in a future article. For those techies interested in the pros and cons of each texture storage format, you can easily find discussions and tech articles concerning them online.

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