Help Needed understanding Gamma/LUT Correction

[Crazy Homeless Guy]

Originally Posted by shaneis

Ahh, I see. You have to email the guy who built it and he will send it to you.

Here's his email address: t.hartmann@infinity-vision.de

Shane,

Can you tell me if this moves the exposure tool to the camera level, or is it still globally applied to the scene?

Regards,
Travis.

[shaneis]

I'm assuming it works at the camera level - quoting from the German MR forums,

"you can save the exposure as a materiallibrary on your hard disk.

Later put a exposure from the Mat-Library in the Camera-Lens Slot under the Rendersettings.

Later put a Mat exposure from the library in the Camera Lens slot under the Rendersettings"

There is also a script http://phpfi.com/312863 that "saves your exposure settings to a library with material naming scheme of the exposure".

Hope this helps,

S.

[dean@pikcells]

Originally Posted by RyanSpaulding

Ah, now I get it! Thanks a ton for that. Would any settings in the VRay Color Mapping need to be changed then? I have all set to default.

yes change the gamma to 1.8 / 2.2 depending on what your using. are u using the vray frame buffer too?

[RyanSpaulding]

Ok, now I'm confused again...

I did a series of tests...

-------------------------------------
Scene 01
Settings from CGA (AJLynn)

Scene 02
Changed ColorMapping Gamma to 1.8 (Dean)

Scene 03
Changed Ouput Gamma to 1.0

Scene 4
Turned off 'Gamma/LUT Correction' and set ColorMapping Gamma to 1.0
--------------------------------------

I never was able to get any of the 32-bit images to match the VRay Frame Buffer's output...and only when I turned off Gamma/LUT Correction did I get the output to match the VFB.

Furthermore, the EXR and HDR saved different outputs with the EXR being even brighter than the HDR and also had AA issues around the objects. Settings to save both the EXR and HDR were left on default ('Use Standard RGB Channel' for HDR and 'No Compression, Float 32-Bits Per Channel, Saved R,G,B,A' for the EXR).

SO below is the output of the study, along with the desired output. I've also supplied a link to download the Max Files, Textures, Output, and Settings. I dont get why NONE match the VFB. Anyone have any ideas?

http://www.graphicacrobatics.com/gamma.zip

[RyanSpaulding]

And now the settings...

P.S. You can see the camera settings in these images...Sun/Sky is left to default.

[AJLynn]

My head hurts. Try the option 1 settings but with the output gamma set to 1 for EXR output (you don't need to output gamma an EXR).

[dean@pikcells]

ok ive just done a test my self, and it seems spot on my end using gamma 2.2.

see attatched images.

the first image shows my max settings, the vray frame buffer, and the max frame buffer. the vray frame buffer ignores max's gamma, and applies the colour mapping gamma. when testing renders, always use the frame buffer as this shows the output. you have to turn if off when net rendering though as you elements dont render with VFB.

the second image shows 4 renders of each file type (jpg, png, exr and hdr) as you can see they are identical. all i have done to the exr and hdr is to adjust the gamma setting in photoshop (image 3)

hope this helps!

[Crazy Homeless Guy]

The problem is what you are seeing in the Vray frame buffer is a gamma of 1.0, with no correction applied to it. Since you are using a gamma of 1.8, you need to apply a correct color curve for the frame buffer so that it displays it correct. Click the first button on the bottom left of the frame buffer. It will bring up a color corrections dialog. You need to adjust this curve so that your Vray frame buffer will display with a correct gamma adjustment.

I opened your first image in PhotoShop. I selected the top left square, and corrected the gamma to 1.8. I then selected the bottom right square, and corrected to a gamma of 0.555 (the inverse gamma of 1.8.) Now all of the square match. What is happening is the the top left square has no gamma correction applied to it, and the bottom left square has a double gamma applied to it.

The Vray frame buffer is slightly more geared to using a gamma of 2.2, than a gamma of 1.8. I say this because they have now included a button at the frame buffer that quickly applies a gamma correction curve of 2.2 to the image in the frame buffer. This is the sRGB button. This did not exist a couple of versions ago, and you had to manually a curve to correctly display the image in the frame buffer. Maybein the future, Chaos will add a 1.8 button, but as of right now, you will need to do this manually.

I don't know exactly what your curve would look like, but when manually applying a inverse 2.2 curve, it looked something like the image attached.



I probably just added another entire layer of confusion to this.



I think you only have to apply the correction curve if you are using a output gamma of 1.0 in your preferences.

[RyanSpaulding]

Originally Posted by AJLynn

My head hurts.

Mine does too.

This gamma stuff is retarded.

[Crazy Homeless Guy]

Originally Posted by RyanSpaulding

This gamma stuff is retarded.

Bingo. In the end all that matters is if the image looks good.

I started using the LWF because I was creating a lot of interiors, and I needed paint colors and lighting to really behave in a way that I had a great deal of control over.