C-Log for XFs?

[Josh Dahlberg]

It's my understanding that the C300 essentially borrows the brains (and codec) from the XF305. Given this, is there any reason Canon couldn't give XF users C-Log via a firmware update?

As someone who grades everything I shoot, a flatter profile with greater dynamic range seems pretty useful to me. I already dial in a relatively flat image - I'm unsure if C-Log can be effectively mimicked by incamera setttings or whether it's doing something "special", beyond the scope on custom presets.

Well, I'm curious, and sure someone in the DV-info community can set me straight on why this can/can't happen for the XF.

Thanks!

[Juan Diaz]

Hi Josh,

I don't work for Canon nor am I an engineer but this is my guess based on experimenting with my XF300:

The C300 does indeed use the same codec and the same custom preset settings (with the exception of the Canon Log option in the gamma settings). But the the sensor on the C300 is completely different and I think that's the key reason why Canon might not choose to offer C-Log for the XF cameras.

Canon has shown that you can create an effective log setting that works in an 8-bit codec, and that got me excited about trying to approximate this on my XF. And what I have found is that it's difficult to create such a setting on an XF without introducing a lot of noise to the image. Also the XF sensors inherently have less latitude than the sensor on the C300 which reduces the usefulness of log encoding. It doesn't matter if you're encoding in log if the sensors aren't capturing the dynamic range that can be recorded!

In any case, I have been able to create some Log-like settings with moderate success. What I would say is that these settings are only useful in certain situations and I wouldn't use them for general purpose recording, because they introduce a bit of noise and compress the critical mid tones.

Those are the two factors I learned you have to manage carefully when trying to approximate a log setting: not introducing *too much* noise and leaving reasonable contrast in the mid tones.

An article that I found useful in creating a log-like setting is this one on Alister Chapman's blog.

Canon C-Log on the C300 compared to S-Log. | XDCAM-USER.COM

In it, he compares C-Log with Sony S-Log (he owns both a C300 and an F3). The bottom line from the article is that Canon's log is more conservative than "true" log in order to work in an 8-bit codec. The highlight handling is similar to the cinegammas and there is a slight boost in the shadows. The raised lower end means that you can underexpose a little more thereby gaining some more highlight detail.

But, underexposing also means that you're recording your mid tones darker, which on an XF means you risk getting noise in the mid tones and exaggerating that noise when you grade the shot. This isn't a problem on the C300 as its sensor is so clean!

Bottom line, approximating a log setting on an XF305/300 seems possible but you have to be conservative in your settings and careful how you shoot.

Here is a test I shot of my D_Log-1 setting before and after doing a quick grade:

Canon XF300 - D_Log-1 Custom Preset Graded & unGraded on Vimeo

This setting does introduce a little noise but it's mostly in the shadows so you will tend to lose the noise when you push the blacks down in grading. The noise is light enough that you can get effective results if you include de-noising in your grade. In this test I used Red Giant's Denoiser plugin for FCP7 which is no longer available. Soon I hope to test this setting with Neat Video's plugin which is highly regarded and available for multiple hosts (FCP, Premiere, AE, Nuke, Mac, Windows, etc):

Neat Video - best noise reduction for digital video

As another note, I'm working on a different log-like setting which might allow me to get a flatter image than my D_Log-1 setting with less noise and less mid tone compression. Not sure yet how well it works; still testing.

Juan

[Chris Hurd]

That's an awesome post, Juan -- thank you so much for making this
reply. I was thinking about how to best answer this question and you've
done a much better job with it than I would have. Much appreciated!

[Josh Dahlberg]

Thanks so much Juan, wonderful reply - everything you said makes perfect sense.

[Juan Diaz]

Wow Chris, thanks! I appreciate that!

Hi Josh, No problem, I hope that helps.

[Josh Dahlberg]

Originally Posted by Juan Diaz

Here is a test I shot of my D_Log-1 setting before and after doing a quick grade:

Canon XF300 - D_Log-1 Custom Preset Graded & unGraded on Vimeo

Juan I like the look of your Vimeo post. Impressive. Care to share your settings - that would be fab!

[Juan Diaz]

Originally Posted by Josh Dahlberg

Juan I like the look of your Vimeo post. Impressive. Care to share your settings - that would be fab!

Hi Josh,

Sure, I'd be happy to. I'm attaching a custom preset (CPF) file for the D-Log_1 preset. You should be able to load it into your camera with an SD card. Never uploaded a CPF file here before so I hope it works!

I guess it goes without saying, but my first post is basically a long list of caveats in the use of this preset! But I've gotten some good results with this preset when I take those into account.

This preset is a derivation of an earlier preset I had made so I've uploaded that one as well (FlmNeg_1). My FlmNeg_1 preset is useable for general purpose shooting. I use it in a wide variety of contexts for cinema style applications. You'd probably still want to grade it as it's a little flat. But it's not nearly as flat as the Log preset so it's useable "out of the box". No caveats!

I made the Neg preset because I wanted to have a cine preset with as accurate a color rendering as possible. So I made it with a DSC Labs cambook, a vectorscope/waveform monitor and some tweaking based on real world shooting.

The Log preset inherits those color settings so I thought you might find this one useful as well.

Happy Shooting!

Juan

[Josh Dahlberg]

That's wonderful Juan,

I look forward to testing these out. Very much appreciated! You really are a champ.

Josh