'Is there a standard equipment path that would allow the DP or DIT to take the Arri LogC signal on set and put it through a standard Arri LogC LUT conversion box to feed a scope in REC 709?'
yep, it's built into the camera as MON output.
C300 has a similar option(menu item) for external 709 monitoring/recording.
All provided details point to not so great exposure/ligthing on set.
BG
From: "bigfish@pacbell.net [Avid-L2]" <Avid-L2@yahoogroups.com>
To: Avid-L2@yahoogroups.com
Sent: Sunday, July 12, 2015 11:52 AM
Subject: [Avid-L2] Re: Avid's Canon LogC LUT seems blown out?
I have tried a few other log choices in Avid like the Arri LogC but things look too saturated. That is interesting that you mention Cannon-Log. In Avid the LUT is labeled "YCbCr Canon C-Log" which led me to believe it's basically a LogC, which I assume is a basic kind of exponential math transform, with some particular elements that tailor it to the Cannon C-300 sensor, or would it be all the Cannon sensors?
I found that the offline editor had also not liked the look of the YCbCr Canon C-Log so he made his own in Resolve. I did this too looking at a cross sections of shots. I took a shot with a bright white cloudy sky along with other shots of interviews and Broll. I had hoped I could find a common ground LUT. I found that the LUTs I made in Resolve translated to Avid well in terms of overall level that I see on my scope. The Resolve SDI output and the Avid SDI output seem to match.
Unfortunately I did not find a universal LUT recipe. The White Sky LUT worked great on the white sky shot in Avid but it was dark for other shots. The other shots worked for the other shots but if I tried the white sky shot it got blown out. In other words I think the exposure is not consistent. I think you are on the right track when you ask about the DP's exposure index. On the Arri site it talks about Arri LogC maps the "scene grey 18% luminance" to a data value of 400. I take that to mean that the log math centers around "scene grey 18% luminance" or a data value of 400. They list how various exposure settings yield stops of latitude above and below the scene grey 18% luminance. I don't really understand what determines "scene grey 18% luminance" is it an absolute value of light like a NIT reading is on a monitor probe.
I am very rusty on film indexes and exposure. Am I correct to think that the index number is similar to film speed/sensitivity to light? And that exposure is the F-stop setting? I've read where F-stops have been replace with more universal numbers that I think are the indexes you mention. Obviously this is not my area of expertise and I spent most of my time with video cameras looking at a waveform to judge exposure.
I'm beginning to feel that the issues I'm seeing, which appear to be similar to others on the list, has a lot to do with improper exposure in the field. Yes the YCbCr Canon C-Log signal does not appear to be clipped but when it's under or over exposed things seem to get harry and preclude the use of a standard one size fits all LUT to bring things back to REC 709. Does this make sense? Would the use of a good ole light meter calibrated to the proper index for YCbCr Canon C-Log to set the exposure result in a proper workflow?
My understanding from DP friends is that the Arri Alexa doesn't really have a lot of tweaks to the sensor and that it's very much like shooting film. That to me implies they are able to use a light meter to set exposure and not judge exposure based on that they see in the viewfinder. That seems like a more consistent workflow than relying on "ON Set LUT boxes that feed a monitor in video village." Is there a standard equipment path that would allow the DP or DIT to take the Arri LogC signal on set and put it through a standard Arri LogC LUT conversion box to feed a scope in REC 709? I realize that footage isn't always destined for a REC 709 world but in my world it is and this would seem to make sense to me.
I found that the offline editor had also not liked the look of the YCbCr Canon C-Log so he made his own in Resolve. I did this too looking at a cross sections of shots. I took a shot with a bright white cloudy sky along with other shots of interviews and Broll. I had hoped I could find a common ground LUT. I found that the LUTs I made in Resolve translated to Avid well in terms of overall level that I see on my scope. The Resolve SDI output and the Avid SDI output seem to match.
Unfortunately I did not find a universal LUT recipe. The White Sky LUT worked great on the white sky shot in Avid but it was dark for other shots. The other shots worked for the other shots but if I tried the white sky shot it got blown out. In other words I think the exposure is not consistent. I think you are on the right track when you ask about the DP's exposure index. On the Arri site it talks about Arri LogC maps the "scene grey 18% luminance" to a data value of 400. I take that to mean that the log math centers around "scene grey 18% luminance" or a data value of 400. They list how various exposure settings yield stops of latitude above and below the scene grey 18% luminance. I don't really understand what determines "scene grey 18% luminance" is it an absolute value of light like a NIT reading is on a monitor probe.
I am very rusty on film indexes and exposure. Am I correct to think that the index number is similar to film speed/sensitivity to light? And that exposure is the F-stop setting? I've read where F-stops have been replace with more universal numbers that I think are the indexes you mention. Obviously this is not my area of expertise and I spent most of my time with video cameras looking at a waveform to judge exposure.
I'm beginning to feel that the issues I'm seeing, which appear to be similar to others on the list, has a lot to do with improper exposure in the field. Yes the YCbCr Canon C-Log signal does not appear to be clipped but when it's under or over exposed things seem to get harry and preclude the use of a standard one size fits all LUT to bring things back to REC 709. Does this make sense? Would the use of a good ole light meter calibrated to the proper index for YCbCr Canon C-Log to set the exposure result in a proper workflow?
My understanding from DP friends is that the Arri Alexa doesn't really have a lot of tweaks to the sensor and that it's very much like shooting film. That to me implies they are able to use a light meter to set exposure and not judge exposure based on that they see in the viewfinder. That seems like a more consistent workflow than relying on "ON Set LUT boxes that feed a monitor in video village." Is there a standard equipment path that would allow the DP or DIT to take the Arri LogC signal on set and put it through a standard Arri LogC LUT conversion box to feed a scope in REC 709? I realize that footage isn't always destined for a REC 709 world but in my world it is and this would seem to make sense to me.
---In Avid-L2@yahoogroups.com, <oliverpeters@...> wrote :
First of all, Log-C and Canon-Log are two different gamma curves. Log-C is only ARRI and is derived from film scan profiles. Canon-Log isn't quite as flat-looking as Log-C. The second issue is what was the DP's exposure index? If the image was exposed at the settings that are optimal for Canon Log, then you should be closer than what you describe. Have you tried other LUTs to see if this is an Avid issue or camera issue? For example, applying a Canon-Log LUT in Resolve or FCP X and see if the image reacts that same way as in Media Composer.
- Oliver
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Posted by: Bogdan Grigorescu <bogdan_grigorescu@yahoo.com>
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this is the Avid-L2
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