[Sidefx-houdini-list] Linear Workflow
emailgeneonthelist at gmail.com
Thu Aug 26 12:08:15 EDT 2010
These threads are always so interesting :)
All you should have to do in Houdini is use a LUT for test renders, and
apply a gamma correction to input texture maps that aren't linear. Then
render to a linear format like exr.
On Thu, Aug 26, 2010 at 8:49 AM, Francois Duchesneau <sidefx at trinix.ca>wrote:
> Great clarification. I'll keep that as a reference because when I will
> think I've figureg it out I'll realize there's still something wrong :)
> > On Thursday 26 August 2010 08:27:06 am François Duchesneau wrote:
> >> This subject confuses me.
> >> I thought Houdini already worked in linear space?
> > It does, inasmuch as it doesn't assume anything other than linear.
> > won't
> > *add* to any existing LUT/sRGB issues, unless you ask it to.
> >> I thought Photoshop only generated sRGB texture so we have to apply a
> >> lut (or a gamma correction to approximate it) when we read those
> >> textures in our shaders?
> > Well, you should, assuming you want to work in linear. When you
> look at
> > your
> > PS image on your computer, it looks "right", that's precisely what
> > Microsoft
> > invented sRGB for, so that would happen. Pop it over to mplay, by
> > default(gamma 1), it looks the same. Thing is, that's incorrect, it's
> > linear. It *should* look "dark" at gamma 1 in order to be linear. The
> > confusion comes about because you're looking at the image through the
> > filter
> > of a monitor that isn't linear, you want to pull that out of the
> > If
> > you set mplay gamma to 2.2, that's a decent approximation of what a
> > image looks like, and by default your PS export will look washed out.
> > want to convert it to linear first(as Gene correctly points out, running
> > it
> > through Nuke and using a Colourspace node to do it is more accurate than
> > simply inverse 2.2, but it's close).
> >> When I read a Houdini image in Nuke. I set the read to linear and my
> >> viewer color space to "none" and my image is exactly how I see it in
> >> Mantra. Nuke works in linear so the gamma correction should be at the
> >> end of it?
> > To clarify, Nuke makes assumptions about the colourspace of your
> > based
> > purely on the file format(this can be tweaked in prefs). By default, a
> > tiff
> > image is assumed to be sRGB and an exr is linear. If you rendered a
> > constant
> > shader of that tiff image in mantra and rendered out an exr, then read
> > both in
> > Nuke, they will look different(assuming default prefs). You should be
> > looking
> > at *everything* in houdini with gamma 2.2, the viewport, mplay, IPR(which
> > you
> > can do now in H11!). You convert your incoming sRGB images to linear
> > first,
> > they will look correct in all those contexts.
> > The above example, you want your Nuke viewer(as a rule, mind you)
> to be
> > sRGB,
> > not none, because just like with mplay set to 2.2 gamma, you want to
> > out
> > all srGB references, then at the tail end you pop your 2.2 gamma or
> > similar
> > LUT in there have it look 'correct'.
> > All of this assumes you want to be working linear, of course.
> > lots
> > of people out there that never do film that live in an sRGB world and
> > can
> > happily go about working as if sRGB is an invisible filter laid over top
> > of
> > every last thing they're working on, since in the end it gets displays on
> > an
> > sRGB buffer(or close). The one downside I would point out, though, is
> > that
> > light behaviour with PBR won't be the same, really I would argue this is
> > good reason to consider linear workflow even outside of film.
> >> Why do we have to set the gamma correction to "Gamma 2.2" to match XSI
> >> linear space????
> > If you're referring to the setting in the ROP that Mario suggested,
> > that
> > does is pour more sampling into the dark areas, it doesn't change
> > colourspace
> > per se. It's a handy trick especially if your final product ends up on
> > TV. I
> > suspect even in film it's handy for certain shots.
> > Nuke's assumption about colourspace based on format drove me mad
> when I
> > first
> > encountered it. Now the Foundry has added the ability to tweak those
> > assumptions and I understand the pipeline, it's actually rather handy for
> > detecting things you're missed. I went through plenty of hair pulling on
> > this
> > topic, believe me. I understand your pain. ;)
> > Cheers,
> > J.C.
> > ---
> > John Coldrick
> > 416-504-0425
> > jc at axyzfx.com
> > -----------------------------------------------------------------------
> > Life does not cease to be funny when people die any more than it ceases
> > to be serious when people laugh.
> > - George Bernard Shaw
> > _______________________________________________
> > Sidefx-houdini-list mailing list
> > Sidefx-houdini-list at sidefx.com
> > https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
> Sidefx-houdini-list mailing list
> Sidefx-houdini-list at sidefx.com
[Gene Crucean] - [VFX & CG Supervisor/Generalist]
** Freelance for hire **
More information about the Sidefx-houdini-list