[Bf-committers] Scene Linear Middle Grey Assumptions

[Matt Ebb]

On Sun, Jul 17, 2011 at 3:00 AM, Troy Sobotka <troy.sobotka at gmail.com>wrote:

> Can anyone cite where Blender's internal representation of middle grey
> is? Has one been defined?
>
> It would seem that for ingestion and output, the reference model would
> be wise to locate one. For example, within Open Color IO, the
> reference compositing space appears to select a value that aligns with
> the optical middle grey value of 0.18[1]
>

'middle grey' is not a photometric quantity and can't really be defined
precisely. It's also important to note that it's not an absolute value
either, it's more of a proportion defined as being between black and a
'properly exposed white diffuse reflector'

The definition they're using in OCIO seems fine, and it's perfectly easy to
just say we can adopt that definition for blender.

That doesn't mean though that anything that's a value of 0.18 must look
'middle grey' on your screen - what you actually see on your screen is
entirely dependent on whatever profile/gamma function is being used to
convert that from linear to display. 0.18 after converting from linear to
sRGB gamma is roughly 0.5, which in an ideal world should give you a
halfway-grey appearance, but that can differ with different profiles,
monitor calibrations, etc of course.


Matt