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[Public WebGL] Re: ETC compression method.

Hi Steve,

The only public description I know of is in the OES_compressed_ETC1_RGB8_texture extension spec. There are presentations that Jacob made to the Khronos Group which would give you the information you are looking for but I cannot turn them lose. Jacob is on vacation until the near the end of this month. Once he returns I'll ask him if he can release one of his presentations.

Note that ETC1 is for RGB. For alpha you'll have to wait for ETC2.

ETC is certainly an unfortunate name from the point of view of web searches.



On 2010/08/09 12:39, steve@sjbaker.org wrote:
It's great to hear that we'll have a compressed texture format available. 
The weakest link in doing web-based 3D graphics is the time the textures
take to load - so this is a critical issue.

Sadly, I have never worked with ETC images (although I know a lot about DXT).

Does anyone know of a readable online description of how ETC compresses
data?  I hate to have to figure it out from the 'etcpack' stuff.  I
presume it's a lossy scheme - and I need to understand how it loses so
that I can advise my artists on when they can usefully use compression and
when they cannot.  eg: Can I compress normal maps without getting horrible
artifacting?  Is it better to store RGB and A in separate maps rather than
trying to compress them together?  What is the trade-off between using
lower resolution uncompressed maps versus higher resolution compressed

A Google search doesn't turn up anything interesting (because 'ETC'
matches 'etcetera') and the Wikipedia article on ETC is about one line
long!  (cf gallons of available documentation on DXTn compression).

  -- Steve


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