@alcomposer

Panasonic soon will be business of selling bare cameras for $100 and later rent you packages of functions for $20 per month.

@Vitaliy_Kiselev

As conversion function exist (LUT is just another form of function) and it will work with ANY (underexposed or overexposed) source data the same. As I said - if you underexposed footage you will get underexposed result, it is all same.

The knee in the LUT gives it a kink that makes it a non-linear curve. For that reason, it will mathematically match the footage precisely at only one specific exposure level. Of course, you could correct an exposure mismatch by adjusting the gain of the footage before feeding it into the LUT, but that would require manual calibration of your post production levels. The LOG-LUT procedure is intended to be a turnkey workflow that requires no technical knowledge on the part of the user.

@Brumbazz I think there needs to be a dedicated LOG thread- this has become epic. In a good way-September 2015 will always be known as the great LOG debate.

You guys need to say which kind of LUT you are talking about.

A camera-to-display LUT is designed for footage shot with a certain exposure level. There are push and pull LUTs designed to properly transform footage shot with a lower or higher exposure level compared to normal.

A camera-to-linear (or camera to true log) LUT doesn't care how the footage was exposed. There's just one LUT for all exposure levels. Exposure compensation is easily applied in a linear or log color space.

@alcomposer

http://www.personal-view.com/talks/discussion/13641/wheres-a-good-explanation-of-v-log#Item_38

Really i dont know how work the LUT.

Hear an interesting use of Lumetri, not is with V-LOG, but can be interesting for general use in post.

@lpowell @Vitaliy_kiselev is not disputing that there is a complex transformation. He stated there is a known transform f(x) and hence there is an inverse transform g(x)

Sensor->f(x)->mp4

We take this mp4 file and

Mp4->g(x)->prores, CineForm...

So what do we gain from log d,c,v whatever... Mp4 is 8bit so we are simply destroying shadow data and giving more bits to mids and highlights.

There is no gain!!

10bit may be a different story. The 99$ is best saved and invested in an external recorder

I might just stick to Natural or Portrait. I won't be able to afford a 10-bit Pro Res/ DNxHR Shogun or Ninja assassin to use a LUT to monitor exposure with. Also, I'm not hearing a lot of good conjecture about V-Log L on the 8-bit internal 4:2:0 codec.

@zcream

So what do we gain from log d,c,v whatever... Mp4 is 8bit so we are simply destroying shadow data and giving more bits to mids and highlights.

Yep, in the V-Log-L thread I pointed out that when converted into 8-bit H.264 format, the bottom four stops of log profile dynamic range are encoded with just 4 bits to cover all four stops. Such a crude level of digitization makes the effort to capture 12 stops of dynamic range futile.

@Vitaliy_Kiselev

Yes, that's exactly what I mean, you can pack a wider dynamic range into an 8-bit data space, but only by sacrificing the tonal range of some segment of that dynamic range. In the case of V-Log-L, it is the tonal range (i.e. image quality) of the bottom 4 stops of shadow dynamic range that is sacrificed.

@lpowell, you've got it backwards. V-Log doesn't capture an extended shadow range. It captures an extended highlight range. Preserving shadows is not futile. It's doing exactly what it should be doing, devoting a small number of bits in the deep shadow part of the V-Log curve for what will be a small number of bits in the corresponding range of the display-referenced final product. The deep shadows are noisy, not because of limited precision, but because of shot noise and sensor noise. You don't want to devote a lot of bits to encoding noise, and can't put your midtones there. That part of the range must be reserved for the deep shadows, and you must expose with that in mind. The bottom two stops will be mapped very close to 0% in the Rec.709 output. Remember that Rec.709 goes right to black, to linear 0.

In practice the limited precision of the V-Log curve will be a non-issue. You'll be more limited by the camera's noise performance.

It's true that V-Log is not optimized for 8-bit recording. But it's not because of the shadows. Every camera log space does the shadows in a similar manner, being close to a power function. V-Log is not optimized for 8-bit recording because of the large log section. Log encoding is not perceptually uniform, and so it's inefficient. Some other camera log spaces were designed for 8-bit recording from the start, and they do the more efficient thing which is to keep a power function for a greater part of the recorded range before transitioning to something closer to log.

@balazer

So long as you don't overexpose your footage, there's no such thing as an "extended highlight range". All cameras will capture the entire highlight range up to the point of sensor saturation, at the finest digitization quality the camera is capable of. What happens after that is determined by the camera's tone curve. In the case of V-Log-L, the linear response of the image sensor is converted into a logarithmic curve, preserving midrange and highlight details in a manner similar to the response of the human eye. Ideally, this logarithmic response would be maintained throughout the entire 12-stop range, but technical limitations make this impractical. That is why a non-logarithmic rolloff knee is imposed on the bottom 4 stops of the shadow range, and the entire curve is offset with a 12.5% pedestal. This 12-stop DR spec thus defines how deeply the dynamic range extends into the shadows before being clipped off at black.

Your claim that "you don't want to devote a lot of bits to encoding noise" is absolutely the wrong approach to preserving shadow detail. The relative increase in noise at low light levels makes shadow details appear more complex to the encoder, and that inherently requires more bits to perserve with high fidelity. In the case of V-Log-L, an 8-bit H.264 encoder will crush this complexity into 4 bits of crude, blocky patterns that obliterate the bottom 4 stops of the dynamic range. What you want instead is an encoder with 10-bit or better precision, and enough bitrate to preserve as many fine details as practical, including as much of the low-level noise as you can preserve. You may then use sophisticated noise management tools in post to extract the highest quality images your workflow can produce. H.264 encoders generally do a lousy job of this, because they are consumer products tuned to favor highlight details and crush shadows into high-contrast blackness. While that may look sharp to untrained eyes, it falls apart when you attempt to lift those crudely digitized shadows up out of the muck. If you don't take care to preserve the tonal depth of your shadows, that vaunted 12-stop dynamic range will be all for naught.

@balazer

the shadow ranges of Rec.709 and of V-Log go all the way to black. (linear zero) Their shadow ranges are unlimited, effectively. There's nothing to extend.

A totally misleading claim. The dynamic range of V-Log-L extends downward to 12-stops below the highlight clipping point of the image sensor. All DR below 12-stops is crushed to black. That crushed range is not "unlimited", it is obliterated.