… why it is a bad idea to use Log for 8-bit Codecs?
The C300 and the less expensive pendant, the C100, booth does have have a really great image sensor with an unrivaled light sensitivity.
But they are outputting only 8-bit shades red, green and blue as do many other cameras like the Sony FS-100, FS-700 and of course DSLRs.
Canon’s C500 has the same “issue” with the internal 8-bit codec, except if you use an external recorder which would then record 10-bit or 12-bit Canon RAW – but that’s a different story.
And why in the hell should you not use the Canon C-Log gamma curve? Actually you can and should use it, but not as intendend!
Like many other Cameras you can adjust the image with Custom Picture styles.
The most popular picture style for Canon DSLRs is Technicolor’s CineStyle which provides a S-type gamma curve for a flatter image to get more details in shadows and highlites and should provide more latitude for later grading. That is theoretically a good thing, but…
The bad thing about it is that this is done within a 8-bit colorspace with 256 shades of grey Canon did it on their Canon S-Log CP as did Technicolor on their CineStyle Picture Style for DSLRs. Read more Detail about Technicolor’s Cinestyle in an earlier article I wrote.
You can download the Custom Picture Styles for the Canon EOS-C100 at the end of the article.
I recently got my Canon C100 and a Ninja2 recorder which records up to 220mbit out of the C100 and has a superiour codec that provides best posible quality for the movies.
With the second most popular picture style, the Canon C-Log, they did nearly the exact same thing like the Technicolor CineStyle for Canon DSLRs, except that the Cinema Series C100/C300 does have a much better sensor to play with.
Dont understand me wrong, the Canon C-Log Custom Picture Style is great and it provides a great latitude, but I think it can be optimized to do a even better job.
But the problem remains. Canon C-Log rises black levels, but you dont get any more details within the dark rised brightness range. So why should we use it, or the better question is why should we use it NOT?
The short answer is: you get more brightness steps and less banding artifacts.
To get more into detail I’ve made a simple test.
I filmed a daylight scene with a nice wide white/blue sky and later watched the Waveformmonitor within Premiere CS6. What I saw prooved my theory again that you loose brightness steps when using the unmodified, original Canon C-Log.
I tweaked the Custom Picture settings in actually 2-ways that made a huge difference!
I turned on the Waveform-Monitor in my C100 and went into Custom Picture settings.
The most important thing is to setup a correct black-level and master-gain. There are two important settings for black-level adjustments:
for the C100 in the CP Menu under Fine Tuning:
Black -> Master Pedestal set to -1
Other Functions -> Setup Level -> Level -3
This basically sets a correct black level and master-gain for the Canon-Log Gamma curve. All other settings are left to default. The lowered gain value also limits the video-voltage to 1 volt – equal to 100% video level. Most important for broadcasting and it’s also a good thing for most nle’s because they dont handle video-levels over 100% very good. Many of them just clip them to 100%. The Level Parameter in the Custum Picture settings instead scales the maximum video-level to 100% and you dont loose details in bright areas!
Then I took the curve-filter in Premiere CS6 and scaled down the shadows until the darkest areas from the sky reaches 0.3 volt – the pure video black – 0/0/0 in RGB.
When I did this with the filmed test material it shows more or less visible steps in the sky. Guess what, most steps I got with the modified Canon C-Log with stretched Gain and Black-Levels!
I got even more brightness steps and nicer colors out of the camera with a even more modified Custom Picture Style for which took the Cine2 Gamma, Norm1 Color Matrix, a Master Pedestal of +14 and Setup Level (Gain) set to -20 and a few other settings. I did a few more changes on that CP-Style which I called NTtc1 which you can download and tewak for yourself if you want or just use it as is.
Not surprisingly, I found out that the worst Gamma setting is the WideDynamicRange (Wide DR) and the EOS-Standard (EOS Std), which should emulate the dynamic range of a Canon DSLR with Standard Picture Profile, which is actually nor really reccomended to use, because it is way too contrasty. So best is to stay with Canon C-Log or Cine Gammas.
The benefit of tweaking the Canon C-Log Custom Picture Style is to get the whole 256 shades of R-G-B and that even helps the later grading, if you want, because you dont need that much of a grading, or just take it as is, because it is not that low-contrast mish-mush like the original Canon C-Log.
When you try to grade certain imagery that is in a way limited in brightness steps (the color-bit-depth) the waveform monitor shows horizontal darker lines. These are brightness gaps which reveals banding much earlier when encoding the movie for heavier compressed material like the MP4/.h264 codec. The bad banding effects are mostly visible in smooth brightness transitions like skies and bigger areas in the image with no structures in it. Structures in the image by the way eliminate banding effects as a workaround.
When the waveform monitor shows smooth transitions between the structures without horizontal darker gap lines, the image quality is fine and not “damaged”. When using material with higher bit-depths, the banding effects are not a problem because unlike 8-bit codecs with 256 brightness steps a 10-bit codec has 1024 brightness steps and a 12-bit codec has unbelivable 4096 brightness steps with which you have nearly endless grading possibilitis.
Try it out, test it and you will see that you can get out even better image quality for your C100/C300 and C500 when recording with the internal 50mbit 8-bit codec from the C300 or even with the 24mbit AVCHD Codec from the C100
The Custom Picture Styles for the C100, if you want to use them on the C300 or C500 just use the text-description below and set the parameters manually or include them into your camera-settings file and import it into the camera.
UPDATE: Read about new versions of my Custom Picture Styles in my new Blog-Post.
Custom Picture NTclog1 : simply the Canon C-Log Gamma Curve and the Canon-Log Color Matrix but with corrected Gain and Black-Level from 0 to 100%
Custom Picture NTtc1 : my former favorite, its a combination of Cine2 Gamma-Curve and Norm1 Color Matrix, again with corrected Gain and Black-Level to 0-100% and pretty vivid colors.
Custom Picture NTtc2a : my favorite at the moment, Cine2 Gamma-Curve and Cine2 Color Matrix, corrected Gain and Black-Levels and some color matrix modifications to create a better cinematic film look.
NEW: Custom Picture NTtc2b : my favorite at the moment, Cine2 Gamma-Curve and Cine2 Color Matrix, corrected Gain and Black-Levels and some color matrix modifications to create a better cinematic film look (improved version of NTtc2a).
WARNING! DO NOT USE WHILE ON CRITICAL PRODUCTION. TRY IT OUT AND TEST FIRST BEFORE USING THE CP-STYLES FOR PRODUCTION!
USAGE: Just copy the files on a SD Card in the directory structure: PRIVATE\C_PICT\ and import them via Custom Picture Menu: Transfer File -> Load from SD -> (A or B) or just set the CP directly from the SD-Card.
The Custom Picture parameters as textual information for manual tuning
Found a typo or mistake, please feel free to inform firstname.lastname@example.org. Thanks for reading.
Article written by Patrick Zadrobilek on 6.Jan.2013 (updated: 12.Apr.2013)