Shooting 4K Log, guidance please
 

I have some basic questions for shooting 4K Log with the LS300...

1) First, run time for a 64GB UHS-II card... at 150mb... I'm looking at around 50 minutes, is that correct?

2) Are you getting good results using just SLR lenses or are the Cine Primes a must for 4K?

I have a Panasonic LH-900 monitor that I trust. I'd need to supply it with HD at, say, 1080P from the SDI output. I assume I can do this when shooting 4K, correct?

The 900 has a very accurate "old school" waveform monitor function.

3) If I expose using this (1080P) waveform (shooting log) to get the proper levels for 70% flesh tone, 90% peak whites am I OK or will this not be proper for in-camera 4K log? This point is a bit confusing for me to understand?

Thanks for the help.

Re: Shooting 4K Log, guidance please
 

Hey George,

1) I think I get more like 55 minutes, but that's from memory. Either way, your estimation isn't far off.

2) I only use Canon DSLR lenses and have never had any quality issues. If you'd like to see some screen grabs/sample clips, please let me know and I can send you a raw file, straight out the camera.

3) I don't use a monitor so can't help you with those questions, but I've not heard of anyone else having issues using a 1080p monitor while recording 4K. - Although I don't think the waveform would accurately represent your image since it's not seeing the same information.

I hope that helps, and I'm more than happy to be corrected if some info isn't quite right.

Re: Shooting 4K Log, guidance please
 

Nick:

Many thanks with the first two questions. Hope I can get some insight into the last one.
Getting the proper levels... this is where I'm really confused.

Re: Shooting 4K Log, guidance please
 

No worries. Getting the right levels isn't too hard. I use the built in monitor and as long as your aware of it's limitations, the thing works fine. With the zebras and histogram on, I basically expose so the histogram reads to the right, so everything a little bright, but also below the zebras, so they're not showing (apart from on something that is going to be blown out anyway, like a lampshade etc.)

Do you have the camera already? I'd suggest doing lots of tests using only the built in LCD.

Re: Shooting 4K Log, guidance please
 

I do not. Belongs to a friend who knows less than I about log. I had it for a week but did not expect to need to use it so soon. I can get it back and I still have time before the shoot.

Here is my take, and I may be way off.

If the camera can shoot 4K log internally and still output "recordable" 1080 (as log) via the SDI it would seem to make sense that external output would be conforming to HD standard in terms of levels. Otherwise it would be a useless video feed. If that IS the case, and I may be way off, then if I set the levels per the scope on that signal, the internal recording should be correct.

Hope someone can chime in on all this.

Re: Shooting 4K Log, guidance please
 

In J-Log1 mode, the LS300 provides an optional 1D LUT that converts the log tone curve to a Rec 709 curve for display on either the LCD or external video outputs. This allows you to get an idea of what the post-processed video will look like on a Rec 709 monitor, but I wouldn't rely on it for setting exposure. The camera's built-in histogram and zebra provide the most accurate indication of exposure levels. The only thing I'd want an external monitor for is manual focusing.

Re: Shooting 4K Log, guidance please
 

Seems when I had the camera last week I tried selecting the LUT and it only shows up on the camera LCD. It does not show up on the SDI. Would that not make sense since, if you were recording that SDI signal, you would not want it to be altered.

Unless there is a "switch" in the menu I did not see. Either way, I get your point.

I need to get the camera back and compare what I see on the internal histogram vs the external waveform. Maybe there is some correlation I can make for my own use. I much prefer using the waveform if at all possible.

Re: Shooting 4K Log, guidance please
 

You're right, thanks for the correction. The 1D LUT option only affects the LCD and viewfinder displays, not the HDMI and SDI video outputs. Here's a link to the patch 2.0 update manual:

http://pro.jvc.com/pro/attributes/4k...LS300_v2.0.pdf

Re: Shooting 4K Log, guidance please
 

So I have gotten the LS300 from my friend for some more "learning" about jlog.

First off, I have a sheet that lists the waveform IRE for some of the other camera models that shoot log from Arri to Canon to Panasonic... but nothing listed for JVC. I know they are new to this.

They put an 18% gray card from 32% to 42% and they put white (matte white card) from 61% to 63%.

Does anyone have the specs for the LS300? I assume it is somewhere within these but would be nice to know the true values.

My method, for the moment, is to use the gray card to set exposure for sit down interviews where there is the opportunity to do that. As I stated in the beginning of this thread, I'm using my Panasonic LH900 monitor with the on-screen waveform. I'm taking this from the SDI out as 1080P and the camera is set to 4K mode with jlog gamma on.

In my testing, setting middle gray to around 38% gives me white around 70% or so with the LS300. That puts the fleshtones (using a magazine image) at around 55 to 60%.

Comments?

Re: Shooting 4K Log, guidance please
 

I've been shooting Log on a building site for the last two days. Run and gun. I just eyeball the image as I go along, watching the histogram sometimes, other times using spot meter. basically pushing the image as bright as possible without it appearing to become too crushed at the high end. It looks like total shite on the camera monitor (as usual), but looks fine when I'm archiving the footage.

Re: Shooting 4K Log, guidance please
 

I cannot take that chance.

I need the subject to be lit correctly. I need to do this by something more than my eye until I have a feel for jlog. I do not have an NLE (that supports LUTs) that I can drop the clip on to and add a look so I am at a bit of a disadvantage at the moment.

Re: Shooting 4K Log, guidance please
 

Well, if you are in control of the lighting you could just shoot in cinema log and then your look is baked into the recording.

Otherwise you could try something like a Ninja Inferno that will process the LUT for you.

J-Log is a really mild Log compared to Sony and Canon. You can very easily setup your monitor to give a good indication of where your image could end up once a LUT is applied.

I've found it to be very forgiving in post, but you really need to see the results for yourself.

Re: Shooting 4K Log, guidance please
 

While that would be appropriate for Panasonic's V-log L, it's underexposed for the LS300 in J-Log1 mode. The GH4-5 highlight clipping point is at around 80% in V-log L mode.The LS300 clips at 109% in J-Log1 mode, after a short knee starting at 98%. If you want to avoid the knee, set Zebra Top to 98% and Zebra Bottom to 90%. There's no advantage to underexposing more than that.

Re: Shooting 4K Log, guidance please
 

So two simple questions.

Where is middle (18%) gray in jlog?

Where do you have your flesh tones set in jlog?

Re: Shooting 4K Log, guidance please
 

Here is a link to JVC's documentation of J-Log1:

http://pro.jvc.com/pro/attributes/4k...l_of_D-LUT.pdf

On page 3 is a tone curve chart and a table of "Reflection" values for J-Log1 which lists "18%" as "35.9% IRE". In my experience, these percentages make no sense for two reasons. In J-Log1 mode, the maximum reported value of "800% Reflection" bears no consistent relationship to zebra, histogram, or actual peak exposure levels observed in internal LS300 video recordings. Whatever "800% Reflection" is intended to refer to is unclear, since the physical property of reflectance cannot exceed 100%:

https://en.wikipedia.org/wiki/Reflectance

As for flesh tones, I try to keep them above 50 IRE, while using ETTR principles to protect the highlights. In J-log1 mode, I have Zebra Bottom set to 98% and Zebra Top set to OVER, and rely on it as a guide to the onset of highlight compression.

BTW: I found JVC's J-Log1 LUT's crude and over-saturated. I recommend the Leeming LUT or FilmConvert's generic Rec 709 LUT's instead.

Re: Shooting 4K Log, guidance please
 

I think JVC is referring to image brightness that is 800% higher than the nominal level coming off of a 90% white source(test chart), which is about 3 stops of exposure headroom. This makes sense as with Rec709, there is about 2.5 stops from middle gray(18%) to peak white(90%), so adding 3 stops(800%) gives a total of about 5.5 stops above middle gray when shooting with J-log. The graph shows about 6.5 stops under 18% and 5.5 over...so 12 stops in total.

When shooting in J-log, I set my zebras to 70-75ire for anything in the scene that is "white" and have had good results.

Re: Shooting 4K Log, guidance please
 

What does "nominal level" of 90% white refer to? It appears to be an arbitrary spot on the tone curve referenced to the arbitrarily-positioned "Stop-0" mark. How can there be 3-stops of DR above 90% white when, by definition, luminance can only be increased by an additional 10%?

Re: Shooting 4K Log, guidance please
 

A 90% reflectance White, like that found on a DSC lab chart, would be exposed to 100ire using Rec709. Using J-log, 90% white is exposed at approx 65ire, and thus allows for approx. 3 stops(800%) of over exposure. 800% would be recorded at 109ire(level 255 in 8bit). Stop 0 refers to 18% middle gray...that's why there is about 5.5 stops above 18%, and about 6.5 stops under.

Re: Shooting 4K Log, guidance please
 

So it appears JVC is following basically the same scheme as the other camera manufacturers as to where white is at around 65 IRE and 18% middle gray at around 36 IRE.

Is this what were are saying?

Re: Shooting 4K Log, guidance please
 

"90% White" seems like a completely arbitrary point approximately 2.5 stops above "18% Gray", which is likewise defined as an arbitrary point somewhere near the middle of the gamma curve. With that scaling, 109 IRE becomes "800% Reflection", which is physically impossible (without amplification). The cherry on top is the erratic behavior of the on-screen "peak" light meter, which in J-Log1 mode can fluctuate between 350-800% while the zebra and histogram are clearly indicating levels over 95 IRE. (I suspect it's actually an area meter that averages luminance levels within its green rectangle.) As we already have an industry standard 0-109 IRE scale, what is the point of these inflated percentages?

http://pro.jvc.com/pro/attributes/4k...l_of_D-LUT.pdf

Re: Shooting 4K Log, guidance please
 

J-log seems to be very similar to the original Sony S-log, which was designed for 8 bit recording.

90% white is not arbitrary, it's a standard for setting exposure and testing the sensitivity of cameras. 800% is used to describe an object luminance that is 3 stops above normal peak white.

http://www.dvinfo.net/forum/attachme...ings-s-log.jpg

Re: Shooting 4K Log, guidance please
 

Yes, 90% White is standardized with respect to Rec 709, but here we're dealing with J-Log1 footage, which has a much broader dynamic range. As a consequence, the 18% Gray standard, which is based on a DR of 5.5 stops, no longer fits. That archaic assumption is what I was refering to as "arbitrary" above.

If not 18% Gray, what should you use as a standardized exposure reference point? Most often, I use ETTR to religiously protect the highlights, particularly when shooting stand-alone events that will not require intercutting with footage from other cameras. As the clips pile up, however, maintaining consistent skin tone exposure becomes a bigger issue than highlight protection. For that I use a conservative version of the Wolfcrow system described below for Sony S-Log2 footage, which is similar to J-Log1. Wolfcrow recommends pushing skin tones up 3-stops to around 60-70 IRE. I think 2-stops is more prudent, with skin tones at around 50-60 IRE. The LS300's Zebra can be set to highlight this or any other IRE range you prefer.

Re: Shooting 4K Log, guidance please
 

Setting the zebras at 50ire for skin tone would probably be a safe bet. Like I mentioned in a previous post, I normally set my zebra to 70ire and expose anything that is white to that. If there is nothing white in the scene, I'll use a calibrated white balance card or piece of paper to set exposure. I find this method is great for keeping the exposure consistent, where as ETTR can be very inconsistent.

I shoot with the Sony FS7 frequently, and use the waveform for checking exposure. It will show level with or without the LUT depending on how you setup the viewfinder...very helpful, especially if there is white in the scene.