Re: [Openexr-devel] OpenEXR vs Raw images

[Rod Bogart]

On Mon, 22 Dec 2003, nkb wrote:

> I did a simple comparision. In terms of file size, for the same image, 
> canon crw file size (in my example) is 4.7MB while openexr format with 
> piz compression yields a result of 12.8MB. 

The 3x size difference is because the CRW has only one channel, and the
OpenEXR has three.  CRW uses a single value per pixel, with an assumed
layout (something like RGRGRGRGRG for even scanlines and GBGBGBGBGB for
odd scanlines).  It is a mosaic sensor, stored in the CRW file.  To make 
an RGB for each pixel, there is a filtering step which blends neighboring 
pixels together.  After this step, you have three times as much data to 
store in the output file.

RGB