[Sidefx-houdini-list] Linear Workflow

Erkan Özgür Yılmaz eoyilmaz at gmail.com
Mon Aug 30 10:39:09 EDT 2010


> 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).
>

a multconstant node is not the node you need but a colorCorrection node with
the gamma is set to 0.4545. just put it in front of any colour input...

E.Ozgur Yilmaz
Lead Technical Director
eoyilmaz.blogspot.com
www.ozgurfx.com


On Sat, Aug 28, 2010 at 1:58 AM, Robert Kelly <isstuff at gmail.com> wrote:

> Magnus you explained that clearly!
>
>
> > 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).
> >
>
> this sounds like a texture input vop that has a sRGB  to linear
> convert toggle like Peter Bomar described is a really good idea. Or
> maybe you just have every image viewer / editor working in linear
>
> On 27 August 2010 05:10, Magnus Pettersson <magnus at stormstudios.no> 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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