[Sidefx-houdini-list] Linear Workflow

Gene Crucean emailgeneonthelist at gmail.com
Tue Oct 5 12:42:08 EDT 2010


As of Snow Leopard, Apple is now using 2.2. *Huzzaah*



On Tue, Oct 5, 2010 at 3:19 AM, Peter Bowmar <pbowmar at gmail.com> wrote:

> Hi David,
>
> This workflow assumes a monitor of 2.2 gamma which is typical of all
> monitors except possibly Apple computers/monitor combos. Those can be
> 1.8 or something like that, though I've heard they're moving to 2.2 as
> well.
>
> So, when you have a linear render you need to apply 2.2. gamma (or a
> LUT) to your Mplay/IPR viewer.
>
> Cheers
>
> Peter B
>
> On 4 October 2010 20:13, David Burton <daland at withatwiststudio.com> wrote:
> > Does this workflow assume the monitor gamma (IE: what I would adjust in
> the graphic card settings)
> > is set to 1?
> >
> > thanks,
> >
> > david
> >
> >
> > On Aug 27, 2010, at 5:10 AM, Magnus Pettersson wrote:
> >
> >> Just to summarize for some people who might still be confused by all
> this
> >> (most likely :P) what to actually do. This is "the ballpark" linear
> workflow
> >> without LUTs and so on. I assume all textures and colors is already sRGB
> >> (2.2) space (if stuff looks good on your monitor, it is most likely in
> sRGB
> >> and need conversion to linear):
> >>
> >> 1. ALL shaders should have their input colors/textures converted to
> linear
> >> -> apply 1/2.2 to all textures and color parameters (including point
> >> colors). In houdini right now it could equal to add a multconstant node
> >> after a color parameter before its piped into something (like a mult
> etc).
> >>
> >> 2. Ok now all your inputs should be correct, time to Render. Now to view
> >> this "in the ballpark sRGB" put the mPlay gamma to 2.2 and this should
> give
> >> you a good appreciation of how your render looks (if your monitor colors
> >> isnt totally wacky then you should go buy/borrow a monitor calibrator!).
> And
> >> this ofcourse means if you watch the picture in mPlay gamma 1.0 it will
> look
> >> dark (because of your monitors gamma correction making it darker).
> >>
> >> 3. When happy with the render looking at it with this mPlay gamma 2.2
> you
> >> can send it off to comp. Like people said Nuke comp artists just take in
> all
> >> your renders with linear space and everyone should be happy :)
> >>
> >> The reason we have this very confusing gamma 2.2 here and 0.454545 there
> and
> >> some makes stuff darker (monitors) and other brighter (like mPlay gamma)
> etc
> >> is because of the EVIL old CRT screens had a negative gamma (technically
> >> limitation) and to correct for this every picture produced, every GUI
> >> produced and most likely every photo taken and every webpage have been
> >> having a 2.2 positive gamma applied (mostly in background without user
> >> knowledge) to correct for the CRTs shortcomings. BUT now a days with our
> new
> >> technology our LCD screens have no problem showing right colors in
> linear
> >> (which would be the best for us in this business so we wouldnt need to
> >> care).
> >> But if LCD screen manifacturers from the beginning would give you a
> screen
> >> in linear space as default noone would buy them because people would go
> "omg
> >> this new technology is crap, everything is ugly!" so they have applied
> this
> >> negative gamma curve to display the content of all programs and all
> internet
> >> "correct".
> >>
> >> Myself would like to see linear becoming the new standard, but that
> would
> >> require all digital content that is shown on a monitor to be chaged. So
> most
> >> webpages on the internet would have to change its colors, all pictures
> >> produced until now need to be converted to linear and so on, which you
> can
> >> understand is a massive undertaking. Not to mention all new content made
> >> needs to be made in linear (photos, programs gui, webpages etc)
> >>
> >> Because of a very small procentage of the people who owns a monitor or
> >> creates the GUI/webpages/images found in this digital age is actually
> aware
> >> of this linear space mumbo jumbo, so seeing a change in this in the
> >> near/distant future is very unlikely so we will have to continue our
> sRGB to
> >> linear (to sRGB) pipeline.. i blame CRT!
> >>
> >> Magnus Pettersson | Effects TD
> >> Storm Studios AS
> >> www.stormstudios.no
> >>
> >>
> >> On Thu, Aug 26, 2010 at 9:23 PM, Andy Nicholas <andy at andynicholas.com
> >wrote:
> >>
> >>> Thanks Edward, yep, I think this is the piece of the jigsaw I'm
> missing.
> >>>
> >>> I need to go away and do some research around all this, particularly
> the
> >>> perceptual bit. Once I set it straight in my head, I'll write a summary
> on
> >>> my website.
> >>>
> >>> Thanks again,
> >>>
> >>> A
> >>>
> >>>
> >>>
> >>> On 26 Aug 2010, at 19:39, Edward Lam <edward at sidefx.com> wrote:
> >>>
> >>>> On 8/26/2010 3:45 AM, Andy Nicholas wrote:
> >>>>>
> >>>>> 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.
> >>>>
> >>>> You're missing the fact that the eye itself also has a nonlinear
> >>>> response. When you put in a 2.2 value into mplay, you're now undoing
> the
> >>>> power curve that the monitor applied, giving you linear _luminance_.
> Do
> >>>> not confuse this with _perceptual_ lightness.
> >>>>
> >>>> If you want *perceptual* (lightness) linearity, then you need to
> >>>> generate an approx. 0.4 power luminance curve [1], explaining why
> >>>> putting an mplay gamma value of around 0.4 "works".
> >>>>
> >>>> Lastly, this issue has nothing to do with Houdini in particular. Take
> a
> >>>> linear gradient in another package (say Photoshop) and you will see
> the
> >>>> same thing.
> >>>>
> >>>> Regards,
> >>>> -Edward
> >>>>
> >>>> 1.
> http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html#lightness
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-- 
[Gene Crucean] - [VFX & CG Supervisor/Generalist]
** Freelance for hire **



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