[Sidefx-houdini-list] Linear Workflow

Daniel Jenkins thedj28 at googlemail.com
Thu Aug 26 06:06:01 EDT 2010


I don't suppose anyone has come across some good reading material for
this topic? I know some of the fundamentals of linear workflow but not
my knowledge is a bit patchy in some places. If anyone can point me in
the direction of a good website / paper I'd really appreciate it!

Cheers,

Dan

On 26 August 2010 10:53, Rangi Sutton <rangi.sutton at gmail.com> wrote:
> 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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