Linked by Thom Holwerda on Thu 7th Jul 2011 20:41 UTC, submitted by sawboss
3D News, GL, DirectX More patent news? Sorry, but for some reason, there's a spike in patent, trademark, and related news this week - not entirely unsurprising considering it's earnings season. HTC, currently under attack from Apple and a recent signer of Microsoft patent agreement regarding Android, has bought S3 Graphics... For the patents. Patents Apple has already been found infringing upon.
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RE: S3 patents
by ba1l on Fri 8th Jul 2011 16:37 UTC in reply to "S3 patents"
ba1l
Member since:
2007-09-08

I don't read these patents, but how Apple can infringe something if:
1) GPU core is from Imagination
2) It doesn't support S3TC AFAIK
PVRTC is based on different scheme.


I just read (well, skimmed) the patents in question. They pretty much describe S3TC, in unnecessarily complicated language, and in general terms rather than specifics.

Essentially, the patents cover texture compression by:

* Breaking an image into blocks
* Quantizing the block so it only has four colours (or three colours + transparent)
* Picking two of those colours as reference colours, such that the others can be interpolated using (unspecified) math
* Encoding each pixel as either a literal colour index, an interpolated colour index, or transparent.
* Storing each block with a header, containing the two reference colours
* Decoding by reversing the process

That's essentially S3TC.

The PVRTC I'm more familiar with (used by the Dreamcast, among other things) is a VQ-based thing, which works by breaking the image up into 2x2 blocks, screwing around with the image until only 256 unique blocks remain, putting those blocks in a dictionary, and writing out dictionary indexes instead of pixels. That one is nothing like S3TC.

However, the PVRTC that the iPhone uses doesn't seem to use this format. The dictionary increases the size of the texture data by a predictable amount, but files compressed with the iPhone texturetool don't seem to have a dictionary. So, it's not the same format.

It looks to be something along the same lines as S3TC (or ETC, or FXTC), but I have no idea how it actually works, and it doesn't appear to be documented anywhere. It could well be covered by S3's patents.

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