Re: [Openexr-devel] Forgot the questions

[Rod Bogart]

On Wed, 05 Mar 2003, Drew Hess wrote:

> Hi Klas,
> 
> OpenEXR doesn't do any explicit log-encoding of data when it reads and
> writes files.  At ILM we use 16-bit FP ("half") and 32-bit FP images and
> have been moving away from log-encoded formats.

Depending on how you look at it, the "half" values are log encoded.  A
log encoding takes a equal number of steps for some multiplicitave
increase.  Since it is a 16bit value representing a mantissa and
exponent, the log is specifically log2.  We have 1024 steps for every
multiply by 2.  This works out pretty well for images that represent
light in a scene, since a "stop brighter" corresponds to doubling the
light values, which is simply incrementing the exponent.

RGB