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View Full Version : MentalRay, lens shader, PrimaryBuffer, RenderPass, Epic Fail


bigbossfr
06-11-2009, 09:48 PM
Hello all,
With my friend Kel Solaar, we discovery an epic fail of MentalRay (or MentalRay for Maya ?).
I'll try to explain.

What do i want ?
I want work in linear workflow and have renderPass, i want my beautyPass is like the masterPass.

First : just a blinn, with a texture and a directional Light. PrimaryBuffer to 32 bits float.
Render in tiff 32bits float.
MasterPass :
http://img200.imageshack.us/img200/2005/baseh.jpg (http://img200.imageshack.us/i/baseh.jpg/)

BeautyPass :
http://img200.imageshack.us/img200/6605/basebeauty.jpg (http://img200.imageshack.us/i/basebeauty.jpg/)

Difference :
http://img200.imageshack.us/img200/4397/basediffrence.jpg (http://img200.imageshack.us/i/basediffrence.jpg/)

Done, all is good, no difference.

So, now, i want a linear workflow.
I put a "mia_exposure_simple" node on the lens of my camera.
Setting :
Pedestal : 0
Gain : 1
Knee : 0.5
Compression : 0
Gamma : 2.2

I put a gamma correct on my texture, i set the gamma to 0.45454.

Master :
http://img196.imageshack.us/img196/4951/lensetnodegammamaster.jpg (http://img196.imageshack.us/i/lensetnodegammamaster.jpg/)

Beauty :
http://img196.imageshack.us/img196/84/lensetnodegammabeauty.jpg (http://img196.imageshack.us/i/lensetnodegammabeauty.jpg/)

I put a gamma correct on my beautyPass in compositing with Nuke. I set the gamma correct to 2.2.
http://img37.imageshack.us/img37/8104/lensetnodegammabeauty2.jpg (http://img37.imageshack.us/i/lensetnodegammabeauty2.jpg/)

Difference with the master :
http://img196.imageshack.us/img196/8052/lensetnodegammadif.jpg (http://img196.imageshack.us/i/lensetnodegammadif.jpg/)

Epic fail.

bigbossfr
06-11-2009, 09:49 PM
So, it is my mia_exposure_simple ?
Ok, i disconnect my mia_exposure_simple, and i connect directely a mip_gamma_gain on the lens of my camera. I set the gamma of my mip_gamma_gain to 2.2.
So, normally, my lens just set my image to gamma 2.2. Normally, the lens will does nothing else because on my mip_gamma_gain, there is just 3 options (input, gain, gamma).
Render.
Master :
http://img196.imageshack.us/img196/4951/lensetnodegammamaster.jpg (http://img196.imageshack.us/i/lensetnodegammamaster.jpg/)

Beauty :
http://img196.imageshack.us/img196/84/lensetnodegammabeauty.jpg (http://img196.imageshack.us/i/lensetnodegammabeauty.jpg/)

I put a gamma correct on my beautyPass in compositing. I set the gamma correct to 2.2.
http://img37.imageshack.us/img37/8104/lensetnodegammabeauty2.jpg (http://img37.imageshack.us/i/lensetnodegammabeauty2.jpg/)

Difference with the master :
http://img196.imageshack.us/img196/8052/lensetnodegammadif.jpg (http://img196.imageshack.us/i/lensetnodegammadif.jpg/)

Wooo, there is the same difference like a mia_exposure_simple.
I can connect what i want to my lens of my camera, it isn't work !
So, the lens shader of MentalRay (or Maya) isn't work. This slot is bugged.

Ok, next workflow.
I connect nothing lens on my camera. I let my gamma correct on my texture (0.45454). I set my primary buffer to 2.2.
Render :
http://img10.imageshack.us/img10/4676/primaruetnodemaster.jpg (http://img10.imageshack.us/i/primaruetnodemaster.jpg/)

Wooo, nothing has changed. It is like my first render with nothing. Ok.

Ok, i disconnect my gamma correct on my texture. Primary buffer correct automatically my texture.
I do nothing, just the primary buffer to 2.2.
Master :
http://img14.imageshack.us/img14/1228/primary22.jpg (http://img14.imageshack.us/i/primary22.jpg/)

Beauty :
http://img14.imageshack.us/img14/7020/prymary22beauty.jpg (http://img14.imageshack.us/i/prymary22beauty.jpg/)

Difference :
http://img200.imageshack.us/img200/4397/basediffrence.jpg (http://img200.imageshack.us/i/basediffrence.jpg/)

Nothing diffirence, but just the texture is in 2.2. It is not a linear workflow. Fail.

Conclusion : it is impossible to work in linear workflow with Maya.

My temporary solution is : set a gamma correct (0.4545) all on my textures, set the primary buffer to 1, and render.
In compositing, i put a gamma node to 2.2.

achoury
06-11-2009, 10:38 PM
hi damien
This subject was discussed here several time, and there is a lot of confusion about working in linear workflow. you may take a look at this thread (http://forums.cgsociety.org/showthread.php?f=87&t=764761&page=1&pp=15).
But If you get exactly the same images between the master (A) and the beauty (B) it's normal that you have nothing when you do difference operation!
because the 02 images are identical ( A = B ) and (A - B = 0)
/Rachid

bigbossfr
06-12-2009, 05:03 PM
Hi Rachid,
I don't know if is the same problem like your thread, but here the probleme is the lens camera slot.
You connect just a mip_gamma_gain to 2.2 on your lens of your camera, without FinalGather, just a little scene, render, and the lens doesn't set your image gamma to 2.2.

achoury
06-13-2009, 12:25 AM
Hi Rachid,
I don't know if is the same problem like your thread, but here the probleme is the lens camera slot.
You connect just a mip_gamma_gain to 2.2 on your lens of your camera, without FinalGather, just a little scene, render, and the lens doesn't set your image gamma to 2.2.
Hi
here is a test without gamma: mip_gamma_gain set to 1

http://www.postmyimage.com/images/images0gV49094.jpg

and here is another one with mip_gamma_gain set to 2.2

http://www.postmyimage.com/images/imagesHIn48939.jpg

/rachid

bigbossfr
06-13-2009, 04:21 PM
Yes and ?

Set a gamma to 2.2 on your first image in compositing, you will haven't the same result like set a mip_gamma_gain to 2.2 on your camera.

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