GH4 to get Log

[Musty]

Log + Shogun + EF Speedbooster = Canon DSLR death!

[tupp]

btw, you can calculate the relative exposure range (i.e. dynamic range) as:
 
relative exposure = log2 ( luminance - reference luminance )

Not sure on this point. Exposure and "exposure range" are two different things. Also, exposure range and dynamic range are two different things.

 

an 8bit file has a max luma range of 256 steps, the binary log of which is 8 (stops).

There is no universal correlation between bit-depth intervals and stops/luma/EV.

Again, 8 bits worth of tones can be mapped to a system with a dynamic range of 25 stops, while 32 bits worth of tones can be mapped to a system with a dynamic range of only 5 stops. Indeed, cameras currently exist in which the user can select 8-bit, 12-bit, 16-bit and 24-bit depths, while camera's dynamic range remains unchanged.

 

So, the value of each bit interval is determined by the dynamic range (or, usually, the amplitude range) of the digital system, along with the number of bits used.

Of course, this scenario is fairly simple on linear response systems. Systems with adjusted response curves (or with randomly mapped intervals) are much more complex.

[andrgl]

8bit log produces banding. This must be for recorders.

[sunyata]

.. Exposure and "exposure range" are two different things. Also, exposure range and dynamic range are two different things.

 

They are different in some cases, but they also have overlap in the context of light in a scene, transparency of film, or sensitivity of a digital sensor.

 

References:

 

"Dynamic range, abbreviated DR or DNR,[1] is the ratio between the largest and smallest possible values of a changeable quantity, such as in signals like sound and light. It is measured as a ratio, or as a base-10 (decibel) or base-2 (doublings, bits or stops) logarithmic value."

 

http://en.wikipedia.org/wiki/Dynamic_range

 

"In photography, exposure range may refer to any of several types of dynamic range..

 

The Light sensitivity range of photographic film, paper, or digital camera sensors.

The luminosity range of a scene being photographed.

The opacity range of developed film images

The reflectance range of images on photographic papers."

 

http://en.wikipedia.org/wiki/Exposure_range

 

There is no universal correlation between bit-depth intervals and stops/luma/EV.

 

No but, in the real world, you can measure relative exposure of anything that emits or reflects light, like between a sheet of white paper and direct sunlight (with a spectroradiometer), which is actually quite huge. Captured by a digital camera, which has it's own dynamic range, and recorded into 8 bit (which has a max of 256 luma levels), the sheet of paper and sun would likely read the same value of 255. So your usable stops have been clipped by your maximum bit depth. If recorded or filmed with a wide dynamic range and encoded into a 10bit Log format (for example) the paper could read as "white" but below 685 (white) and the sun could read over 685, or "over white". LDR and HDR files / workflows refer to dynamic range in this other context. See Cineon, DPX, OpenEXR or LDR vs HDR rendering pipelines etc.

 

Reference:

 

"Conversion of DPX code values to relative scene luminance

relative luminance = 10 ^ ( (dpx code value – white point) * 0.002 * negative gamma )

Commonly, the negative gamma is assumed to be 0.6 (density) and the white point is set to 685.

The result is relative luminance where the reference white is placed at 1.0. To convert into a format like 16 bit TIFF the luminance values are multiplied by 4095 leaving a headroom of 4 stops for the highlights."

 

http://www.acvl.org/digital_intermediates/dicompanion/ch03.html

 

 

Indeed, cameras currently exist in which the user can select 8-bit, 12-bit, 16-bit and 24-bit depths, while camera's dynamic range remains unchanged.

 

The dynamic range of the camera doesn't change, but the range or color depth of what you've recorded does, which has a direct impact on how much you can push the footage in post and the level of dynamic range you can effectively use. 

 

Anyway, I think the post above sums up what I'm saying about bit depth: "8bit log produces banding. This must be for recorders.".

[GMaximus]

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.

I'm sorry, i've never did it. That's just what i've read about it:

I know the directors want total control over their image and I do respect the colorists suggestion and their hard work. But still with the low budget shoots , where you don't create a LUT for every scene beforehand and can't afford a monitor with custom LUTs, the DPs are losing control shooting on LOG.

Advice to producers - the 30 second version
I don't have time for a grade; I want a finished picture straight out of the camera: Use Standard Gamma 5 (STD5)
I / my editor will be grading it on our in-house edit suite: Use Hypergamma 7 or 4 (HG7 / HG4)
It's being finished in a dedicated grading suite, by a full-time colourist: Use S-log

S-Log:
Exploits the full range of the F55 chip, but must be graded by an experienced colourist. Easy to over-expose; read up before shooting. Sony says S-log has 1300% dynamic range, capturing 14 stops of latitude.

Nate Weaver: It's pretty simple. Hypergammas make an image that is kind of "ready to go" from an editorial standpoint. It's intended for people who like to paint their cameras and create in-camera what gets seen in the final product. Intended for minimal color correction.

S-Log on the other hand is intended for folks who want the cleanest, un-adultrated image going into post. Full sensor dynamic range, no matrix "looks" in the camera, no sharpening, nothing. The philosphy of "raw" but still recorded into a video signal. It also assumes there is somebody in post who has the tools and skills to make a pretty image, most likely a colorist.

In post production as the curve is so close to Cineon you will be able to use almost any Cineon compatible LUT’s or Looks. It’s also very, very close to Arri’s Log-C curve so LUT’s designed for Log-C will work very well with SLog3 and Sgamut3.cine making it much easier for many colourists to transition from cameras like the Alexa or a film based workflow to material from the F5/F55.

---
 

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.

So what's the workflow?
Do you just nail the exposure and then use some standard LUT (or de-log) in post - and voila - the colors are right?
Or do you need to create a LUT for every scene before you shoot?
Do you have to spend days of work on the colors only if you create a unique palette?
For example, if someone shoots with F55, slog3 - and then simply applies Cineon compatible LUTs - will there be a good film-looking result, without extensive color corrections?

[jgharding]

I've worked with Alexa LogC, Canon Clog, Sony sLog in post and on set, the real difficulty is exposing correctly.

 

Because of the way a log gamma bends the response of the camera, it's easy to overexpose, even though exposure looks right on screen, so expose conservatively or you'll put the skin and the like on the severe end of the log curve.

 

In post, it's best to source an LUT for your chosen log as a starting point, and work from there. 

 

For Canon Log, the Abel Cine Clog to Wide DR Full Range is best. For Alexa Clog, Arri's website contains all the LUTs you need. For Slog you can get away with Cineon LUTs as a starting point.

 

To answer the specific situation there, you'd recover the scene as it was shot, with the extended highlight benefits of log. So once you apply your LUT your colour saturation returns, you have full black and white and it'll look more like it would had you shot in Rec709, except you'll have more highlight range to play with.

 

If you overexposed on set, the LUT will clip out the tops. With some LUTs you can just pull back the highlights and recover, be aware that some just slice ff your overs though, so experiment. 

 

In 8-bit, yes it's much harder to use log, because the colour space is very unforgiving. Canon are clever about how they do 8-bit in some way, so it's pretty good. Alexa is better of course. 

[sunyata]

So what's the workflow?
Do you just nail the exposure and then use some standard LUT (or de-log) in post - and voila - the colors are right?
Or do you need to create a LUT for every scene before you shoot?
Do you have to spend days of work on the colors only if you create a unique palette?
For example, if someone shoots with F55, slog3 - and then simply applies Cineon compatible LUTs - will there be a good film-looking result, without extensive color corrections?

 

JG covered it IMO with the LUT's etc.. the only thing I would add is, with respect to getting a "good film-looking result", I personally think the GH4 is going to look more like video, regardless of log or color, when there is rapid motion. The inherent sharpness could be a giveaway too, so you could consider at times adding blur with a motion vector filter like reelsmart, and/or add grain from a common film stock (at the end of your workflow so you have control over density and color) . Just my 2 cents.

[gelaxstudio]

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...

 

Unlike common gamma Log Files ,Cine-D file does not require a native ISO,and there is no official technical info explain how it work to reserve more DR,so thinking of it as a gamma profile is much like a joke <_<  

[jgharding]

That chimes with what I've seen, all the tricks to get more DR don't get much more DR.  The tones get shifted about but the exposure points are the same. Once you unsqueeze the image you're almost back where you started.

 

A log profile with a CUBE LUT to go with it, and some official info on exposure point would be ace.

 

Canon, Arri, Sony, Blackmagic Design, all have log profiles, Panasonic needs one across the board too.

[AaronChicago]

Shooting LOG with the BMCC has been so much easier after I bought a DP7 monitor that supports LUTS. Being able to see scopes and exposure of the frame with a LUT added has been a lifesaver.

[64mulford]

I hope this is true. Cine D is terrible for colours.

[deezid]

I hope this is true. Cine D is terrible for colours.

So true.

Cinelike D is a mess. Orange/Magenta color cast with ugly compressed skintones which make people look like zombies... :(

 

Would like to see something like Slog2 or BMCC Log on this otherwise nice camera. ;)

[gelaxstudio]

SONY a7s s-log2 test HD 1080p：

 

I don't think that it is necessary to compare the cinelike profile with S-log2 now,S-LOG2 is really a tool for work!

While cinelike profiles are NOT ! 

[Ari]

If you say so, gelaxstudio, but I personally have never tried these kinds of curves, and I wouldn't know what you can or cannot do with them. So for me it would be useful to see how much you can do with a cinelike profile. With my still cameras I alway s shoot RAW.

 

BTW, I'll probably end up getting a GH4, but for now at least they are very hard to obtain and out of stock everywhere locally.

[AaronChicago]

So true.

Cinelike D is a mess. Orange/Magenta color cast with ugly compressed skintones which make people look like zombies... :(

 

Would like to see something like Slog2 or BMCC Log on this otherwise nice camera. ;)

 

You guys must be handling the footage improperly. Skintones are outstanding with Cine D if you use the proper white balance and film LUTs. You also have to bring down the midtones a tiny bit.

[johnnymossville]

Personally I haven't had much luck with Cinelike D yet.   Standard, Natural and Cinelike V are nice so I'm sorta hiding there for now.