I have absolutely no idea what any of this means but if someone figures out a good way to interpret the footage in Premiere i'll be grateful.

Big thanks to @mash and @Mckinise, who provided me with a bunch of V-Log L footage.

GH4 V-Log L Measurements

• V-Log L maps middle grey 2/3 of a stop lower than Standard does at the same ISO setting. To be consistent with Standard, ISO 400 in V-Log L should have been called ISO 250. (I measured 0.64 stops difference)

• In V-Log L, the camera's built-in exposure meter reads 2/3 of a stop higher than it does for Standard if you want middle grey mapped the same way. When the meter reads +0.0, it should say -0.7. (confirmed in firmware v2.3)

• V-Log L has 1 and 1/3 stops more highlight range than Standard photo style at the same ISO setting. (measured 1.30 stops)

GH4 V-Log L Exposure Guide

• Set the photo stye to Standard. Using an ISO setting of 250 or higher, adjust the ISO and the exposure until the image looks well exposed. Then increase the ISO by 2/3 of a stop and switch to V-Log L, keeping the same exposure. This will roughly match the middle grey levels between V-Log L and Standard. V-Log L will have 2/3 of a stop more highlight range.

• If you use the camera's built-in exposure meter in V-Log L, aim for an exposure reading of +0.7.

• At low and medium ISO settings, shot noise dominates over read noise. Therefore the exposure is the most important factor in determining the overall noise level (much more important than the ISO setting). To minimize noise, strive to maximize the exposure, reducing the ISO setting and/or overexposing as necessary while still trying to maintain any highlights that you don't want clipped.

• If your post workflow supports exposure compensation, you can overexpose the shot and compensate in post to further reduce noise. Expose 1 stop higher than you would in Standard to match its noise performance. Expose 1 and 1/3 stops higher than you would in Standard to match its highlight range.

• These guidelines apply whether you are referring to the Varicam V-Log/V-gamut manual, or using the Panasonic V-Log ACES IDT, or using the V-Log-to-709 LUT. They all map middle grey in approximately the same way.

GH4 V-Log L Assessment

• The gamut matches V-Gamut quite well. Color accuracy looks good (precision issues aside), and is much better than Standard. Standard is a lot less standard than I thought, doing some unexpected things to color saturation.

• The optoelectronic transfer function matches V-Log somewhat well. There are noticeable deviations: blacks are too low; other points on the curve are too high. In practice it won't be a big problem.

• V-Log L in 8-bits lacks precision, which is particularly evident in the color difference channels. Expect to see pink, green, purple, and yellow splotches and banding in low saturation parts of your images. 10-bit recording should fix that.

• Panasonic made the base exposure index 400, which is a bizarre choice. It effectively pushes all levels down, leaving one third of the V-Log curve unused and exacerbating the color precision problem over a larger range of shadow values. There's absolutely no reason Panasonic couldn't have set the base exposure index higher and utilized a greater portion of the V-Log curve, at least at ISO settings above the minimum. It shows that the Panasonic engineers don't really understand log color spaces.

• Recorded videos have the video_full_range_flag set, just like a standard photo style recording made with a luma setting of 0-255. That's not how V-Log is specified in the Varicam V-Log/V-Gamut manual. V-Log specifies Rec.709 ranges, with 0% RGB using a code value of 64 and 100% RGB using a code value of 940. The difference is largely academic, especially in V-Log, which doesn't saturate the color difference channels. But it's another example of Panasonic engineers failing to understand what they were doing.

• The Panasonic V-Log-to-709 LUT maps from V-Gamut correctly and maps middle grey correctly, but renders images with low contrast compared to a straight Rec.709 rendering. It is suggested only for previewing or as a starting point for grading.

Personally, I think Panasonic really screwed up in making V-Log L. They missed an opportunity to make a log camera space that would work well for the majority of its users. As it stands, the quality of 8-bit recording is severely compromised.

V-Log L ACES exposure test video:

V-Log L ACES exposure test video:

V-Log L ACES ISO test video:

V-Log L vs Standard ACES test video:

I have posted my Sony Vegas Pro OpenColorIO configuration with the V-Log color space used in all of these tests: http://www.jbalazer.com/aces-in-sony-vegas

Trees and leaves yet again. GH4 VLOG-L 8-bit internal shot with Voigtlander 42.5 f0.95 @ 2.5 and Olympus 75mm f1.8 @ 3.5. Graded with Avid Media Composer with no Luts.

Thanks for the helpful discussion folks..

I am confused too..

Why would Panasonic not understand that mapping data across a narrow range is going to have a heavy impact on the 8bit image? Maybe they do know but don't care? That would seem odd because most of their users record internally to 8bit. Maybe it is capped for a reason (encoder limitations etc)?

There are some reports that the DVX200 got an update to their v log version (that effectively increased saturation).

Maybe it would be a good idea to indicate to Panasonic what updates to v log (or alternative log versions for testing) would be helpful for GH4 users?

Do I have to create (how?) a LUT for Natural that mimics V-Log colors?

That's actually possible. How easy or hard it is depends on weird or standard Natural's color encoding is. I tried the same thing for Standard, and it turned out to not be easy because of the weird things Standard is doing. Maybe I should try again with Natural.

So is V-Log as big a let-down as VW's diesel engine management system? Surely it wouldn't have caused them too big a problem to use the whole 8-bits for data? (Yes, I'm getting a bit fed up with posterisation effects in the sky...)

Ok - so got my official V-Log upgrade from panasonic. No more 'custom' for me. Histogram now seems to work as before at the highlights, but blacks seem to still clip somewhere before the left edge of the box. mmm odd..

Also - Zebras - shall I set this to 100% ? It seems that 80% is still 'overexposed' for V-Log with my quick tests.

skies are a mess, but I'm assuming they'll always be

I've been testing and doing some math and V-log doesn't record even close to 8-bits of data which would explain the banding and macroblocking. Every profile on the GH4 records 256 luminance values which equals out to 8-bits(Since 32 values in a bit and 8-bits*32 Luminance values per bit=256 Luminance values total) but V-log L records blacks at a value of 30 and whites at 190. Now to change that to bits: 190(Highest value)-30(Lowest value)= 160 Total values in the V-log image. 160 Total luminance values/32 Luma values per bit=5-Bits. So when you record in V-log you're actually only capturing 5-bits of data. For color you're capturing 256 different color values per channel (256 Red, 256 Green, and 256 Blue values) but in V-log with 5-bits of data you're only getting 2(Black and white)^5-Bits=32 different colors per channel. The only reason Panasonic is doing this is because they want V-log in the GH4 to match the same bright and low values of 30(black) and 190(white) as the 12-bit Varicam 35. Why didn't Panasonic just optimize V-log for the 8-bit GH4? It would've be EPIC!

@tedbrah Keep in mind that V-log is very similar to the Alexa log curves. Panasonic have not done anything unusual in the bits used for log capture. It is unusual to shoot 8bit log in the pro industry. I would think that Panasonic are expecting most users of V-log to be shooting 10bit on an external recorder.

I have done some more testing in bright sunlight with blue skies. The result is great! The overcast days did not look very nice but I think if you expose to the right and take some care in grading the results are spectacular.

One thing that is very different from standard profiles:The log curve means available light variation on 'run & gun' footage means the LUT will some times require a pre-lut adjustment to put the exposed range in the correct part of the log curve.

Overall I'm more impressed than I was with earlier tests.

I hope Panasonic actually takes the time and optimizes v-log for the GH4 specifically in future updates....otherwise this is just unfortunate.