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View Full Version : How to deal with cineon log in Blender?

orozimbo
12-02-2008, 10:03 AM
Hi guys, I finished my animation in SD, made and aprooved the first cut. Now I have to render in HD to make the print to film. The finish house adiviced me to deliver the images in cineon 10bit log.

The problem is I donīt have experiency in film and a very few in log images. So I need to understand how to evaluate the results. I try to use de "cineon converter" plugin in after effects and it turns out a odd surprise:
- A image render in linear luminance in Blender converted with "linear to log" looks different than the very same image render in log in Blender.

Is it corrected? Shouldnīt it be the same? Any one has some idea?
Guilherme Lopes
theotheo
12-02-2008, 12:59 PM
If your render from blender is gamma corrected (what most people think is linear) sRGB you need to convert it to linear. either by doing a gamut convert or a simple de-gamma by 0.4545.

Then you can convert from lin to log , make sure you're doing all the converts in float (16 or 32 would do) as that helps keeping the quality of the colours all the way.

Save as 10bit dpx in log format and you should be fine.

-theo
orozimbo
12-02-2008, 03:22 PM
Theo, Iīve beem studying the gamma issue and you helped a lot. Although the results now are more similar, they arenīt the same.

I apply a level effect with gamma 1,4545 and a linear to log converter. Yet, the blender log file have a more washed look. The blender internal render are diferent than aftereffects effect?

Well, I attached 2 small render images of my project in Blender, just to check if Iīm not doing any thing stupid.

Guilherme Lopes
theotheo
12-02-2008, 07:35 PM
Well, if you have rendered out with srgb and want to convert them to 10 bit log you have to go convert you render by doing the de-gamma (0.454545..) and convert that lin to log and save out a 10 bit dpx.

If you want to view that 10bit log dpx you have to convert til from log to lin and re-apply the gamma. Since gamma is "raised to the power of" the inverse of 0.454545 is not 1.454545 its 2.2. Well technically not inverse but you get the idea.

Have a look here :
http://en.wikipedia.org/wiki/Gamma_correction

Hope that helps!

-theo
orozimbo
12-03-2008, 04:02 PM
YYYYYYYYYYES!!! I feel like stupid know, īcause the informations around gamma explain so much what Iīve been through late years (well, later than never!).

Definetly the "linear" images render in Blender follow sRGB specifications, I apply a de-gamma (with level effect) around 2.5 and the lin to log converter - both images match perfectly. As soon as sRGB have a variable gamma I assum that it can provide some visualisation on the 10 bit log cineon render.

Nevertheless, It raised a new question. If Blender is multi-platform, wich compilation has a different gamma encode in render?

Well, anyway! You helped me a lot, Theo.
Thank you!
theotheo
12-03-2008, 11:00 PM
No worries dude :)
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