GH4 to get Log

[rndmtsk]

According to 4/3 Rumors, a reliable source says "Gamma Log" is coming in a firmware update.

 

http://www.43rumors.com/ft4-gh4-firmware-upgrade-will-add-gamma-log-and-dave-dugdale-leaves-canon-for-the-gh4/#disqus_thread

[AaronChicago]

Nice. Does anyone know what the difference in Gamma Log and CineD flat could be, other than saturation?

[Perplex]

can anyone explain what Log means altogether? and the difference between it and LUT?

[sunyata]

In mathematical terms Logarithmic scale is:

 

"... a scale of measurement that displays the value of a physical quantity using intervals corresponding to orders of magnitude, rather than a standardlinear scale. The function of the curve may include an exponent, which is the source of its curved nature."

 

Translation, it's a curve.

 

In digital camera terms it usually refers to a profile curve that is built into a camera's firmware that is going to select the bits to encode from the scene, to the eventual file, but that file will be recording 256 (or fewer) integers if it is an 8bit format. If you want to retain the typical full range (and have it be usable) of a camera's log profile, you will want to encode to 10bit. Most log profiles consider middle gray as 18%, not 50%, because our eyes see 50% as almost white, and require 10bits to cover the full range. Log profiles often look "flat" and can vary in their "flatness" based on the profile. The original source of the flatness was not desirable as much as necessary to reproduce a print and include more dynamic range, but it also can allow more details to be drawn out, assuming you have the color depth.

 

So basically, a log profile might not be desirable when shooting rec709 8bit, but this is the source of much (much) debate.

 

A LUT is a color lookup table and has more to do with post and changing the way you interpolate a file, although it can be used for lots of other conversion needs. 

 

Gamma log seems redundant to me, I'm confused by that one, that's kinda like "Scientology", i.e. the study of science. 

[tupp]

If you want to retain the typical full dynamic range (often using film print density as a rough target) of a camera's log profile, you will need to record 10bit or higher. Most log profiles consider middle gray as 18%, not 50%, because our eyes see 50% as almost black, and require 10bits to cover the full range.

 

The rest of your post is excellent, but these two lines are not true.

Bit depth and dynamic range are two different and independent properties.  Bit depth is the number of tonal/amplitude steps in a digital system.  Dynamic range gives the usable amplitude range relative to noise (similar to signal-to-noise ratio), and dynamic range applies to both digital and analog systems.

To illustrate how bit depth and dynamic range are independent, consider that 8 bits of tonal intervals can be mapped to a system with a dynamic range of 25 stops, but, by the same token, 32 bits of tonal intervals can be mapped to a system with a dynamic range of 5 stops.

Furthermore, a film emulsion (or analog magnetic tape) can have a dynamic range of, say, 7 stops, but that emulsion (or tape) will have no bit depth -- it's analog.
 

[GMaximus]

can anyone explain what Log means altogether? and the difference between it and LUT?

standard, cine- and log-gammas

http://www.xdcam-user.com/2012/07/why-nailing-your-mid-range-will-make-post-production-happy-even-with-cingammas-and-log/

[Darktide Media]

Really excited about this and I feel like it will come out right when the Shogun launches. Log is amazing but most people who dont know how to color have no need for it, also like others have said it will be best when doing 10bit. The cool thing is that we have a small camera that can do 10bit and might now have a Log Curve, making it a whole new beast. 

[rndmtsk]

Gamma log seems redundant to me, I'm confused by that one, that's kinda like "Scientology", i.e. the study of science. 

 

Yeah, this confused me a little too. Does sound redundant. I think it's just a matter of the writer not understanding the lingo... Although admittedly I've never fully understood why one log curve is different from another. Like why is log in the blackmagic cameras so much flatter than Log C in Canon cinema cameras? Obviously for practical reasons it's harder to deal with such a flat curve when shooting 8bit, but I've never really gotten it from a mathematical standpoint.

 

Really excited about this and I feel like it will come out right when the Shogun launches. Log is amazing but most people who dont know how to color have no need for it, also like others have said it will be best when doing 10bit. The cool thing is that we have a small camera that can do 10bit and might now have a Log Curve, making it a whole new beast. 

 

My thoughts exactly!

[Michael Ma]

I wish Panasonic did the GH3 users a solid and gave us Log and focus peaking.

 

And also the updated RW2 format with embedded thumbnail like the GH4.  And made lower the input gain for shotgun mic audio by -5dB.

[GMaximus]

Really excited about this and I feel like it will come out right when the Shogun launches.

Aren't those Cinelike- profiles "loggy" already? This roumor sounds to me like they're going to introduce another log profile.

Log is amazing but most people who dont know how to color have no need for it

If you shoot log, you NEED a colourist ) There are plenty of GH4 vids at Vimeo shot Cinelike- and shouting - i don't know what to do with the colours! )

[sunyata]

The rest of your post is excellent, but these two lines are not true.

Bit depth and dynamic range are two different and independent properties.  Bit depth is the number of tonal/amplitude steps in a digital system.  Dynamic range gives the usable amplitude range relative to noise (similar to signal-to-noise ratio), and dynamic range applies to both digital and analog systems.

To illustrate how bit depth and dynamic range are independent, consider that 8 bits of tonal intervals can be mapped to a system with a dynamic range of 25 stops, but, by the same token, 32 bits of tonal intervals can be mapped to a system with a dynamic range of 5 stops.

Furthermore, a film emulsion (or analog magnetic tape) can have a dynamic range of, say, 7 stops, but that emulsion (or tape) will have no bit depth -- it's analog.
 

 

Yes, I didn't mean to imply that bit depth and dynamic range are somehow the same property, or that film actually contains an inherent bit depth, since of course it's an emulsion and not digital. 

 

Yeah, this confused me a little too. Does sound redundant. I think it's just a matter of the writer not understanding the lingo... Although admittedly I've never fully understood why one log curve is different from another. Like why is log in the blackmagic cameras so much flatter than Log C in Canon cinema cameras? Obviously for practical reasons it's harder to deal with such a flat curve when shooting 8bit, but I've never really gotten it from a mathematical standpoint.

 

It's just the profile that the vendor thinks works best with their cameras since it's all somewhat arbitrary. Log C encodes middle gray of 18% to a code value of 400 in a 10bit signal. The total max values can vary though based on exposure settings. 

.

[GMaximus]

Yeah, this confused me a little too. Does sound redundant. I think it's just a matter of the writer not understanding the lingo... Although admittedly I've never fully understood why one log curve is different from another. Like why is log in the blackmagic cameras so much flatter than Log C in Canon cinema cameras? Obviously for practical reasons it's harder to deal with such a flat curve when shooting 8bit, but I've never really gotten it from a mathematical standpoint.

Those gammas are intended to be used in different shooting and production situations:
http://www.johnhoare.tv/f55gammas.htm
http://blog.abelcine.com/2013/01/18/sonys-s-log2-and-dynamic-range-percentages/

[sunyata]

humm, "gamma log!" not to be confused with "Gamera log"..

[jonpais]

I wish Panasonic did the GH3 users a solid and gave us Log and focus peaking.

 

And also the updated RW2 format with embedded thumbnail like the GH4.  And made lower the input gain for shotgun mic audio by -5dB.

Panasonic has given us focus peaking - on the GM1, the G6, the GX7 and the GH4. I think they've already made it quite clear they won't be adding it to the GH3. I agree with you about the input gain though - it's way too high, especially if you record live music.

[jgharding]

I don't think Cinelike D is full log, it is slightly flat though.

 

You don't need a "colourist" to shoot Log Gamma, I'm not sure where that comes from. You just need to learn a few things a colourist would have to know.

 

Log gamma is a bumped logaritmic gamma curve effectively squeezing in more dynamic range. If you start in post with a purpose-made LUT you'll be in normal gamma again and you can grade from there, or you can grade from log if you like. Using it doesn't require that you make your living exclusively colouring commercial footage!

 

It's worth noting that you get more tolerant highlight protection in log, but unfortunately it becomes even harder to nail exposure correctly. 

 

So if you're going to shoot log, spend some days in post correcting different shots so you get a feel for it.

 

You should also ignore talk of "legal" unless you're delivering for TV directly. Lots of people talk about "legal" ranges on shoots to make themselves sound important and experienced. A web only video which is going to be graded does not need legal capture, it needs best exposure for the selected gamma.

[sunyata]

btw, you can calculate the relative exposure range as:

 

relative exposure = log2 ( luminance / reference luminance )

[pietz]

wouldnt there only be an advantage of using log over cinelike-d, if it improved dynamic range? i would question that a simple firmware update would have the power to do so...

[jgharding]

It kind of does improve it using gamma. It doesn't improve the range of the sensor, but squeezes in more highlight range by bending the gamma.

[Darktide Media]

Cine D and V are in fact a Flat Image that most people are finding good to grade, the reason LOG is needed is the fact that Panasonic is making it, so it will be the best way to get the most of of the sensor for sure. Just look at SLog vs going Flat in the camera, if you know what your doing Slog can be amazing compared to flat, and no im not saying flat is bad.

[hankdendrijver]

Cine D and V are in fact a Flat Image that most people are finding good to grade, the reason LOG is needed is the fact that Panasonic is making it, so it will be the best way to get the most of of the sensor for sure. Just look at SLog vs going Flat in the camera, if you know what your doing Slog can be amazing compared to flat, and no im not saying flat is bad.

 

I tested the different Cine profiles on my GH4 and to my surprise both Cinelike curves don't show any more DR than Standard does. It's a sort of reversed S-curve, upping the shadows end and suppressing the highlights, but with black, white and grey at the exact same spot. It's an image that LOOKS flat but hardly contains any additional DR. Oh, and the colours get screwed up in these profiles, don't know why. Curious about this new log, hoping there is highlight lattitude to be found. I'm not betting on the shadows, they're quite noisy already...