Clipping Issues With Fusionviewlut And Log-lin Viewlut
Posted 15 August 2012 - 01:55 PM
Basically LUT nodes and the 'Display View LUT' are producing different results with the same LUT files
The Display LUT seems to be clipping highlights (bad), while the various LUT nodes do not (good)
I use nvidea geForce gtx 285 as my graphics card. I'm not sure if this is the issue.
It is particularly bad using ARRI LogC. If you look at the A/B image bellow you can see that the sky in the A side is clipped while the B side is not.
The view of the first CineonLog1 node is clipped buy the Display view LUT. Even though the color Inspector still shows the colors to be super white (i.e. R,G, and B all have values above 1.0)
This is an issue because I have LUT files generated by the Quantel artist. He has designed a 'look' for the show and sent me LUT files to take me from Alexa DXP 'ARRI LogC' files to 'Rec709 with the Look'
For me to use a Linear workflow I need to find a way to go from 'Linear to 'ARRI LogC' and then 'ARRI LogC' to 'Rec709 with the Look' using a 'Display View LUT'
Fusion makes it simple to add two display LUTs but the clipping is a big problem for my workflow.
You can see in the image below that the 'Display View LUT' on the left is producing a clipped image compared to the right image using the LUT from the Quantel artist.
I've tried making my own LUT to using the LUT cube nodes. The clipping is still present.
Are other people having clipping issues with the view LUT ? Do I need to replace my graphics card, or is it a problem with the FUSE ?
- KenDadeCind likes this
Posted 16 August 2012 - 12:15 AM
I can't help with the real issue, this looks like the graphics card just doesn't support values > 1 in its shaders. Maybe the viewer's are set to 8bit? maybe a driver issue, maybe just an old graphics card? Maybe somebody else knows (tech @ eyeonline.com for sure)
Posted 16 August 2012 - 04:13 AM
I'm thinking about a graphics card upgrade. Do you see this kind of problem on your system? What card are you using?
I'll ping eyeon a mail and see what they say..
Many thanks for your help.
Posted 16 August 2012 - 08:34 AM
Check your preferences, too. Global->Tweaks->OpenGL. Try Disabling the view LUT Shaders, or making sure you use float16 textures?
If you DO get a new video card, I might suggest a low-cost Quadro so you can use the 10-10-10-2 framebuffer. 30-bit monitors are cheap nowadays, and having a trillion colors may appeal to the types of folk like us who notice clipping and quantization.
Posted 16 August 2012 - 10:09 AM
So I guess the settings macro suggested by Tilt stills seems the most versatile fix. Until I upgrade.
My old nvidea geForce gtx 285 still works well for most things. When i upgrade I was going to focus on CUDA cores and a big frame buffer for my 3dsMAX work.
On paper I'll get significantly more bang for buck from a new geForce gtx 680 than from a Quadro 4000. Now I'm scratching my head...
Posted 24 September 2012 - 11:00 AM
I've had a chance to test a Quadro 4000. It has the same issue as my geForce gtx 285. Honestly I think the 'Lin To Log' Operation in fusion's 'Log-Lin view LUT' is broken. I'm going to post a test .comp file. When I do I'd love some feedback.
For now I've found this FUSE http://vfxpedia.com/...aV3LogC_VS.fuse which works perfectly without clipping.
Posted 29 September 2012 - 06:58 AM
Posted 29 September 2012 - 12:03 PM
Posted 29 September 2012 - 12:28 PM
My AlexaLogC fuse doesn't clip and it's a straightforward implementation of the formula and the Viewshader API.
Posted 02 October 2012 - 06:51 AM
As an aside I note that if you save the script with the stacked luts then read it back in only the bottom lut is restored. No big deal, just thought I'd mention it.
Can't seem to attach the jpeg - "attach files" in normal editor doesn't work and "attach files" in the "advanced uploader" returns an "error500". In any case the results match up to Kenzor's first post.
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