[Sidefx-houdini-list] Linear Workflow

Rangi Sutton rangi.sutton at gmail.com
Thu Aug 26 05:53:15 EDT 2010

On 26 August 2010 18:13, Rangi Sutton <rangi.sutton at gmail.com> wrote:

> On 26 August 2010 17:45, Andy Nicholas <andy at andynicholas.com> wrote:
>> Hi Craig, thanks, yep, that's what I'm doing already.
>> You know, I thought I understood all this linear colour workflow business.
>> What endlessly confuses me is when people talk about gamma and gamma
>> correction, as I'm sure these terms are often used interchangeably in
>> articles when they shouldn't. One puts the colour to the power of the value,
>> while the other puts it to the power of the reciprocal of the value, and I
>> can never remember which. (Jordi did send me a pretty good link to a GPU
>> Gems article that seems to explain it, so I guess I need to commit that to
>> memory)
>> What also didn't help my understanding was by putting Houdini's colour
>> correction gamma setting to 1/2.2 it made a pure linear ramp (defined by a
>> shader) in Houdini look correct in the render (i.e. an even distribution of
>> black through white), but using a value of 2.2 made it look anything but
>> linear and over exposed the dark areas. I still haven't honestly figured out
>> why 2.2 is the correct value to be using, except that it matches our
>> existing workflow in XSI which we've been using for ages. If anyone has a
>> good explanation of that, then I'm all ears.
> Most computer monitors correct to 2.2, while most images are stored
> compressed at the recipricol gamma of ~0.45. Most images we deal with these
> days are sRGB, which is gosh darn close to 2.2. I don't know if much
> software actually expands out the real sRGB curve.. I think mostly stuff
> gets displayed "close enough" with a monitor correcting to 2.2.
> http://en.wikipedia.org/wiki/Gamma_correction
> You can take the gamma correction 2.2 off your monitor, (man xgamma on
> linux, clicky clicky montior setting on them other OSs..) but pretty much
> everything else will look like puke except for your linear renders! Favoured
> approach is to leave your monitor at 2.2, and gamma correct in mantra so you
> have a linear looking result, as you've got!

Whoops.. I meant "and gamma correct in mplay"..

> Well, real favoured approach is to use colour management software, so you
> have a 3D LUT for your particular montitor. But that's for someone who
> actually knows their colour to rant about..
> HTH,
> r.

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