Help Needed understanding Gamma/LUT Correction

[Crazy Homeless Guy]

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]

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]

My head hurts.

 

Mine does too.

 

This gamma stuff is retarded.

Edited May 21, 2008 by RyanSpaulding

[Crazy Homeless Guy]

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.

[RyanSpaulding]

Excellent. It works now. Thanks a ton.

 

I'm going to create a captivate video of this now so we dont have to go through this all the time.

 

What's happening with the EXR that objects that have an edge that meets the VRay sky are jagged?

[RyanSpaulding]

http://www.graphicacrobatics.com/vray_gamma

 

Also in downloadable format (14mb):

http://www.graphicacrobatics.com/vray_gamma/vray_gamma_setup.zip

 

Let me know if you have issues. There's no audio btw.

[Crazy Homeless Guy]

http://www.graphicacrobatics.com/vray_gamma

 

Also in downloadable format (14mb):

http://www.graphicacrobatics.com/vray_gamma/vray_gamma_setup.zip

 

Let me know if you have issues. There's no audio btw.

 

I think that is a very nice video, and illustrates everything covered.

 

Did you get your issue straitened out with the sky and the edge of the alpha channel? I can't remember the exact settings, but I beleive it has something to do with pre-multiplying.

 

Also, if you upgrade to CS3, make sure you hang onto your EXR PhotoShop importer from CS2. Adobe messed with it, and it always makes the alpha transparent in the image. Kind of like Targa images.

[RyanSpaulding]

Yep, exactly it. You need to check 'Pre-Multiply Alpha' for this issue to go away.

 

I'm still going to create a better video...I think it'd help to have audio to explain things. Plus, I can give credit to those intended.

[Tim Saunders]

I thought I was done with this topic, but it opened up a new problem that I just can't seem to figure out.

 

I set up this test scene for experimenting with exterior architectural glass.

 

Everything works fine and dandy when I use a Vray sky for the environment map, but once I replace it, the sky is hardly reflected in the glass. What's up?

 

Yeah I know the glass is WAY too reflective, I was exagerating the reflectin because I couldn't see the hdri reflecting. I have tried Jpegs and I get the same problem. Notice the Vray sky reflects fine.

 

Any thoughts?

[Crazy Homeless Guy]

Why not use a Vray HDRI shader instead of the HDRI in a bitmap slot?

 

...but anyway, you need to use a multiplier with the HDRI. I think it is typically around 20, but I can't remember exactly. You would think that if a HDRI represents real world lighting, then a multiplier of 1 would be what is required. ....but that would make sense, and we will have none of that in this thread.

[Mike.]

hi, just in case you were wondering,

it seems that in case of making strip network rendering on multiple machines, the gamma settings don't need to be configured in each one of the machines;

it seems quite logic, as the input files were pre converted to 2.2, the display of the materials was 2.2 while setting up the materials in max, and the output file gamma was specified during specifying.

confirmation or negation welcome.

 

Cheers

[markf]

I have read and re-read this thread and watched the cool captivate video. I did some limited testing on my own. I'd like to know that I have my system configured "right" and just go on with my work. As has been said by others in this thread, "this stuff makes my head hurt."

 

I don't know if my post will offer any help or whatever but here goes.

 

I have a dual monitor setup, two Dell 2007FP bought at the same time. Using Win XP Pro, NVidia GeForce 8800, Max 2008, Vray. (Have Max 2009 installed but not using yet.)

 

I have a Monaco Optix hardware calibration device and have calibrated my monitors to Gamma 2.2, which I understand to be the Windows standard. This process has it's own set of idiosyncrasies and gottcha's, but I seem to have the monitors matched pretty well and my prints look pretty close to the images on the monitors.

 

I have some links to my test images below. these are screen captures comparing the Frame Buffer in Max to the same image open in Photoshop. And comparing the Max Frame Buffer to the Vray Frame Buffer.

 

http://www.openrangeimaging.com/test-posts/Max_Frame_Buffer-Photoshop01.jpg

http://www.openrangeimaging.com/test-posts/Max_Frame_Buffer-Photoshop_Gamma_Correcirton_Enabled01.jpg

http://www.openrangeimaging.com/test-posts/Max_Frame_Buffer-Vray_frame_Buffer01.jpg

 

I am unclear why, if my system is calibrated to gamma 2.2, I should be using gamma 1.8 in Max. Regardless, of whether I have the gamma correction enabled or disabled the images look very similar to me in Max and Photoshop. The minor differences are most apparent to me in the shake shingles, red brick at the right and the green grass in the foreground. In general the images appear, to me, slightly more saturated in Photoshop, but still pretty close to how they look in Max.

 

I also find that maps in viewed in Photoshop can look different when applied to a model and rendered in Max, some maps more than others. I assume this to be a function of lighting conditions and maybe some GI bleeding.

 

In summary, it seems that having the enable gamma unchecked gives me as good or better match between Max Frame Buffer, Vray Frame Buffer (using Reinhard color mapping and no gamma correction) and Photoshop vs. using Enable Gamma with gamma at 1.8 and bitmaps input and output bitmaps 1.8.

 

Also I 'm just rendering to jpg, tif or tga and haven't messed with exr or hdr.

 

I hope this doesn't add to the confusion and if anyone cares to comment on if I have this "right" or not or any other advice it will be much appreciated. Thanks!