Rendering linear/srgb confusions

[fxnurbs]

Hiya, I am not a novice and totally understand the formats in compositing but i don't get them in maya.
i am trying to render exr as float linear to work them in nuke. but what i render is still the same colorspace than a jpeg
loading my exr in nuke wil give me flat colors and forcing them to be interpreted as srgb give me back what i should see.

i have no fancy shaders or exposure materials, i just try to output my exr linear.
I have try to find any gamma correction in maya all seems to be on 1 in mentaray framebuffer, as if even my jpg would be linear if i trust that.

can anyone who actualy know what's wrong give me little help ?

thanks

[joojaa]

How do you KNOW your jpeg is srgb? You using maya 2011?

See the error of thinking can happen at many levels. It can happen in your texturing stage, it can happen in your render tuning stage, or it can happen in your compositing stage. Just because you tell the computer data to be something doesnt mean it IS in that space, it just means the computer will think it is. Its your job to make sure it really is.

forcing them to be interpreted as srgb give me back what i should see.

Well that can just indicate thet you havent configured nuke to show you the colorspace properly. Likewise it can indicate that you have by mistake made your scenes or anywhaere down the line on the presumption that what you see is correct, even if it was not.

totally understand the formats in compositing but i don't get them in maya.

Err either you dont get them at all or you get them both. However you might get them in way thats technically worng but happens to work out for you while your in the comp end, because the material youve used has allways ben flagged correct.

srgb give me back what i should see.

Err.. is that should see or what you expected to see. Heres the thing, if you TOUGHT wrong going in maya your thinking wrong here too.

See exr is not necceserily linear, its literery whats put into it, see nothing says I cant flag data as linear and still pour nonlinear stuff into it. Also a jpeg can be linear no problems, it can eb lienar even if its tagged srgb. User error happens all the time, the only way you can be sure that a picture is what it says it is if it comes forma source that actually is calibrated/profiled to be what it says it is.

still the same colorspace than a jpeg .
as if even my jpg would be linear if i trust that.

Well yes it would probably be, maya does in no way try to convert the colorspaces unless you tell it to. Maya doesnt care about file  specifications. No computer does you must make sure you adhere to it.

PS: its easy for you to test and measure. Just make a bw linear ramp background and measure points on it. If its linear your file is in the space you assume it to be.

[fxnurbs]

well, your pointing on the jpeg was fair enough. The answer is so simple that i don't anderstand therer is no more info about that or linear workwlow in maya :

everything out of maya is indeed linear, jpeg, exr, whatever.
we have inheritate of the time where everything was done a bit the easy way.
 to have a truly a linear workflow in maya all the inputs files tex... must be converted in lin (that's where most of thing come in srgb usually)
obviousely you will need a lut on your screen or a gamma on a lens shader in maya to see the rgb colorspace with your screen.

my mistake was to assume that the way i was working in maya was right.

by doing that, when importing in nuke all the workflow will be linear all the interpretations will be correct.

in the meantime for those who don't want to convert all the textures in linear and work with lut. it is also correct to apply a colorspace node set to srgb to lin in nuke after all your exr, to apply a compensation gamma on them (don't use the read interpretation as due to a limitation, it will clamp the high values to 1)
i may be wrong, but with few tests with ramps and color corrections, i didn't notice any breaking of the ramp regularity that would have indicated a wrong interpretation.

[joojaa]

everything out of maya is indeed linear, jpeg, exr, whatever.

no, everything out of maya is what you instructed it to compute. the computation of renderers assumes that simple arithmetic of 1+1 = 2 but that doenst mean thet the textures or lightening models you supplied are linear.

we have inheritate of the time where everything was done a bit the easy way.

Yes. But thenagain no. For the artist it may be making things harder after all he SEES something akin to srgb all day and may react to it. If he does its SRGB

to have a truly a linear workflow in maya all the inputs files tex... must be converted in lin
  (that's where most of thing come in srgb usually)

Well, if your data sources are cameras and scanners. Oetherwise no not really depends on what the artist was thinking.

Since not all rendering needs physical accuracy and the user may rely on HORROR looking at the result when tweaking values. then it may be that what comes in goes out fo maya IS SRGB

all the inputs files tex

well not ALL this may or may not apply to bump/spec/normal etc maps. But might. Certainly does not apply to stuff thet come out of say mudbox, however input to theese maya need to be linearized.

my mistake was to assume that the way i was working in maya was right.

indeed. In fact the hardest thing about profiles is NOT waht they do but what people were thinking when they used them. Even people in a purely fixed managed color system like photoshop -> indesign users FREQUENTLY screw up. even tough it should be automatically handled. So the hard way doesn't help becasue the last step computer to human eye, eye to brain doesnt carry profiles.

So its about what you thinking not about what is. Thats why its, very very hard to get right. all it takes is for one person to think different and it all collpses*. THINK ABOUT THAT.

*pun intended