J-Log samples on Vimeo

[Dave Bittner]

Dan Chung has posted some interesting tests using the J-Log settings in the GY-LS300 -

JVC GY-LS300 4K ITU709 and J-Log1 ISO Tests on Vimeo

JVC GY-LS300 4K J-Log Film Grade Examples on Vimeo

JVC GY-LS300 J-Log1, ITU709 and Cinema Gamma Skin Tone Tests on Vimeo

I'm interested to know what the workflow is for J-Log footage is.

[Dave Bittner]

Here's the article supporting the videos -

News Shooter | IBC 2015: Meet J-Log- JVC’s new log format

[Marcello Mazzilli]

Does somebody have the ORIGINAL FOOTAGE (not VIMEO compressed upload) coming from the LS300 ?

Ideally I am interested in the same footage with J-LOG1, one version coming from internal 8bit recording and the second one recorded from the HDMI 2.0 10bit RAW output.... but anything will do as a start.

Thanks to any who can help

[Lee Powell]

What are we looking at here? In the top video Dan Chung shows J-Log1 footage labeled as ISO 200 and 300. Unless there was a secret menu option included in his pre-release firmware, there is no way to select anything below ISO 400 in J-Log1 mode. This video was uploaded to Vimeo a year ago and there has been no explanation or comments added.

In the linked article from Sep 2015, Matt Allard makes the following claim about J-Log1 dynamic range:

"...a traditional REC709 gamma, without using a knee or slope, should hit its limit at 100% reflectance of light. This means in theory that J-Log should allow you to capture a brightness value that is 8 times greater than that of a REC709 gamma."

Even without delving into the math, simply switching the LS300 into REC709 mode will show that its maximum reflectance level is 400% in that mode rather than 100%. But as far as I can tell, what these lofty percentages actually refer to is anyone's guess. When you switch into J-Log1 mode from REC709 mode, the camera's firmware automatically doubles the REC709 ISO setting you were shooting at. This numerical math fudging alone could account for the displayed max reflectance value doubling from 400% to 800% as well. This firmware quirk makes no sense and to the casual user, makes it appear that J-Log1's minimum ISO is 800. The camera's actual minimum is ISO 400 in both REC709 and J-Log1 modes.

Taking it down another level, what reference point does "ISO 400" actually refer to? In the case of the LS300, it corresponds to 0db gain, the base level sensitivity of the camera. But that's not an external standard, it's an arbitrary analog gain level determined by JVC's video signal processing circuitry. They could've just as consistently labeled it ISO 200 or 800 instead of ISO 400, and scaled their "maximum reflectance" percentage accordingly. In the real world of light transmission and reflective surfaces, light reflectance cannot exceed 100%!

The bottom line however, is that in practice, the LS300's percentage reflectance indicator is unreliable and misleading when used to set exposure. It produces drastically different readings in direct sunlight versus subdued indoor lighting. In numerous trials, I attempted to find some consistent level (far less than 800% in J-Log1 mode), below which highlight clipping was guaranteed not to occur. I finally gave up and turned the useless thing off, the inflated numbers it reports are meaningless and do not reliably correspond to the exposure levels indicated in the LS300's zebra and histogram displays. My conclusion is that it is yet another example of inflated marketing hype, not specific to JVC but rampant throughout the industry.

[Marcello Mazzilli]

VIMEO compresses video. I am asking of the file directly out of the camera.. No grading.. but also NO RECOMPRESSION

[Duncan Craig]

By the way the LS300 HDMI output is not 10 bit and I don't think RAW is the right way to describe it either.
I'd happily send you some Log footage but I don't own an external recorder, so you wouldn't have any externally recorded material to compare it to.

[Marcello Mazzilli]

On the web there seems to be some confusing info on the 10 bit. This is sad news from you.
Is the HDMI output any better than the recorded version (a part from not being compressed)? Is sampling higher (4:4:4 ?)

Still... Yes thank you. It would be nice to view JLOG1 files out from the camera, maybe in different situations. Day, low-light, high motion (example: rain to view how the 150mbit in 4K handle it). I don't expect you having everything.. just asking :)

Thanks, Marcello

[William Hohauser]

I would suspect that the color encoding is 4:2:2 which is the standard for the HD-SDI output on the camera.

[Phil Goetz]

There is some original media linked out on this thread that I shot J-log.

http://www.dvinfo.net/forum/jvc-4k-p...-week-two.html