RE: [Openexr-devel] packing rgba into 32 bit int.

[Eric Soulvie]

 I'll give that a shot.   

No, nothing special a about the 128 meg size.   Just what my 3k image
came out to.

     Eric
     Blizzard Cinematics


-----Original Message-----
From: Florian Kainz [mailto:address@hidden 
Sent: Thursday, July 07, 2005 11:04 AM
To: Eric Soulvie
Cc: address@hidden
Subject: Re: [Openexr-devel] packing rgba into 32 bit int.

Eric Soulvie wrote:
> We're mainly using the tiled format to dynamically load chunks of 
> large images at render time.  With RIP maps, these files can easily 
> exceed 128 megs using the HALF type.  For many of these image the
range is not
> important.   I was wondering if anyone has anyone tried packing RGBA 
> into an int  and using a single channel?
>  
>     Eric
>     Blizzard Cinematics
> 
> 
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Instead of packing RGBA data into an int, I would recommend quantizing
the 16-bit data so that only 256 out of the 65,536 are used.  You can do
this by converting your image to 8 bits per pixel and then back to
16 bits.  The quantizing operation can be implemented efficiently using
class halfFunction.  The resulting OpenEXR file should compress to
approximately the same size as if you stored actual 8-bit data. (At ILM,
we tested this a while ago.)

If you pack RGBA data into an int, tools that filter and resize images,
for example, exrmaketiled, will not work very well because they won't
recognize the integer data as packed 8-bit samples.

Is there something special about the 128 meg size?

Florian