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Technical

A dynamic way of working: shooting 4K with Canon Log

A dynamic way of working: shooting 4K with Canon Log

© Canon Europe

November 2016

CPN writer James Morris explores how Canon Log modes work with Cinema EOS 4K footage to provide maximum workflow and grading flexibility...

One of the side effects of the rise of the digital cinema camera is vastly increased light sensitivity compared to film. The huge CMOS sensors in cameras such as Canon’s Cinema EOS models can pick up detail in a much wider range of lighting conditions than film cameras, and also the video cameras that took over the TV industry in the 1990s. When shooting with a regular preset, the dynamic range is limited to provide a typical balance of shadows and highlights, for example to conform to the BT.709 standard.

But so much more is available from the CMOS sensor that you don’t necessarily want to decide so narrowly in advance which part of the range is captured. You can take advantage of a CMOS’s native ability by shooting in a RAW mode, where available, but this produces huge file sizes and has significant processing overheads. A more effective option is a log gamma mode, which preserves much of the dynamic range without the hassle of RAW. Canon now has three options that provide a perfect partnership for the capabilities of the Cinema EOS system, particularly when shooting 4K and high bit depths. In this article, we will look at each of these Log modes and discuss how to fit them into a streamlined workflow.

Canon Log

The original Canon Log arrived alongside the EOS Cinema range, although it’s also available on some Canon DSLRs that have the ability to shoot video, starting with the EOS-1D C. The mode expands dynamic range to 800 percent, providing 12 stops of latitude. For the original EOS C300, this is as compared to 300 percent dynamic range without the Canon Log setting, or six stops when using BT.709. The most obvious use for Log is when shooting in tricky lighting conditions where there are high contrasts between bright and dark areas, because it reduces the chance that important detail is missed out by over- or underexposure.

© David Corfield

Canon has a range of HDR and 4K reference displays which offer true and accurate colour, making them a vital part of the grading workflow when shooting with Canon Log.

Since the introduction of log gamma modes, cinematographers are getting increasingly used to shooting with them in every occasion. But there is a downside, or at least something that must be considered. Because of the way a mode like Canon Log picks up more detail in shadows and highlights but flattens the contrast, it makes the job of grading more involved. Virtually all footage will need to be colour corrected in some way during post-production, but Log footage needs much more sophisticated attention than simple adjustments of low, middle and high levels.

One particular issue is that because shadows are brought up, this can make digital noise more noticeable. This can be fixed during grading, but a better option is 'Exposing to the Right'. This is where footage is overexposed by a stop or two, so that shadows are cleaner. The exposure can then be brought down during grading to produce the required shadow appearance. But greater thought is required with this technique, as you’re imagining the end result rather than seeing a close preview of it, unless a monitor with a representative look-up-table (LUT) is available to keep an eye on things.

The benefits of Log far outweigh this extra labour, however. Whilst relying on “doing it in post” is not a recommended strategy, Log footage provides maximum creative potential at the grading stage. With much more detail available across the dynamic range, grading software such as Da Vinci Resolve or Adobe SpeedGrade can be used to get a wide variety of looks from the same raw footage. From noir-style high contrast to classic 35mm Technicolor, it’s much easier to dial out part of the range for greater contrast than find detail that wasn’t there in the first place. However, there are now two more Log modes available on the latest Canon EOS cameras, so let’s turn to these to see how they differ from the original version, and where they are best used instead.

Canon Log 2

Canon Log 2 is quite different to the original Log. Providing up to 15 stops of dynamic range, Canon Log 2 has a curve that is a lot flatter, and whilst the 18 percent grey values are similar to BT.709, it’s higher than for Canon Log, so that shooting in this mode will require alternative LUTs and suit different lighting situations as well. But the extra three stops over Canon Log means Log 2 can provide even more grading flexibility.

Cinematographer and Canon Explorer Simeon Quarrie had an early experience with Canon Log 2 via the Cinema EOS C300 Mark II, using the camera for an athletics shoot. This was precisely the situation where Canon Log 2 can be particularly beneficial, as he was shooting a dark subject against a very bright background. Quarrie shot using the base ISO 800 for Canon Log 2, but has subsequently found that Log 2 works extremely well with ISO up to 2,500, because the dynamic range is maintained and noise is reduced overall.

Quarrie’s experiences show that 'Exposing to the Right' is a good strategy particularly with Log 2 to avoid the potential noise issues of a log gamma curve, although recent firmware updates for the C300 Mark II has shifted this slightly, so that now it’s optimal to expose more centrally. This is of great benefit, because it’s not recommended to push blacks down too much during post-production, as this can cause colour breakup.

© Blackmagic Design

Professional editing software such as Da Vince Resolve ingests footage shot in Canon Log and displays it before and after grading.

Either way, even with the latest firmware, using Canon Log 2 requires a lot more thought and consideration than Log and it’s necessary to take time getting exposures right. This equates to a more cinematic workflow, with slower-paced shoots rather than 'run and gun'. But the addition of Canon Log 2 can really turn the EOS Cinema C300 Mark II or C700 into cinematic workhorses, with true digital film shooting characteristics and flexibility.

Canon Log 3

Canon Log 2 is an evolution of Canon Log, but the extra shooting considerations mean that it is not the perfect choice in less controlled shooting environments, for example documentary work. This is where Canon Log 3 comes into play. It is intended to provide many of the benefits of Log 2, but with the greater flexibility of Log.

It could be argued that Canon Log 3 sits somewhere between the original Log and Log 2. It offers 14 stops of latitude, so a little less than Log 2 but much more than Log. However, if you look at the graph of its curve, Log 3 follows Log until around 0 stops from 18 percent grey, so will have characteristics that are very similar to Log when handling detail in shadows. This means that, like Log, there will be much less need to “Expose to the Right.”

© Canon Inc.

This graph shows the three Canon Log settings compared to a BT.709 brightness curve, illustrating the relative latitude available from each.

However, Log 3 doesn’t supersede Log 2. It’s likely that it will be preferable over the original Canon Log in most cases, but where workflows are already in place for Log, or grading needs to be matched with footage already shot in this mode, Canon Log is still available. Log 3, like Log, will be a better choice than Log 2 in lower light environments, and both could even be used with relatively little grading now that visual tastes have moved over to a wider dynamic range appearance.

Simeon Quarrie argues that you don’t need to shoot with the blacks as high as possible using Canon Log 3, but can expose with the blacks approximately where you want from the outset. Exposure can be adjusted so that blacks are just a fraction above normal black, so they won’t need to be brought down in post. Canon Log 3 can therefore be used for 'run and gun' shooting where Canon Log was used before, and where you want to do only a small amount of grading but still require flexibility. It’s ideal for when you need to work at speed.

Canon Wide Dynamic Range

There is one more choice, which was introduced to some of the earlier EOS Cinema models with a firmware update but is standard on more recent models. It’s called Wide Dynamic Range, and it still provides a 12-stop dynamic range, like the original Canon Log. But the curve remains closer to a non-log one over a larger portion of the brightness input range, so that footage can be viewed ungraded and won’t exhibit the same flat look that ungraded Log footage usually has.

© Canon Inc.

A typical editing suite consists of several monitors and a mixing desk, allowing the editor and grading technician to monitor colour accuracy.

However, whilst Wide Dynamic Range is ideal when you absolutely don’t want to grade, Canon Log and Log 3 can achieve similar results but provide that extra flexibility should it be needed. So these, particularly Log 3, are increasingly being employed instead, because it’s always safer to have that little bit of extra detail across the range when required.

Bit Depths, 4K and LUTs

Recording a high dynamic range goes hand-in-hand with higher bit depth. If your picture spans a greater difference in brightness levels, a finer gradation of the steps in between is essential. Although you will still get plenty of benefit from shooting a Log mode with 8-bit recording formats, 10-bit is preferable, or even the 12-bit options now available with the EOS Cinema C700. This is particularly true when using Log 2 and 3, with their even greater dynamic range.

The higher bit depth reduces any banding where there are fine gradations of brightness. For example, a sunny sky will contain many different brightness levels. You need a large number of variations to get a nice transition between them. With 8-bit video, 'Exposing to the Right' in these conditions could be a particular problem as the video format might not be able to pick out detail in highlights even if the log gamma mode used can.

For similar reasons, the higher bit rate of the recording format the better, since higher compression will throw away detail, which is counterproductive when the curve being used is trying to preserve it. The 810Mbits/sec available from the Canon EOS Cinema C700 in 4K is optimal. As explained earlier, Canon Log 2 is particularly suited to cinematic shooting, so goes hand-in-hand with 4K footage. In fact, the Canon EOS C700 will actually select Canon Log 2 by default when recording raw to its Capture Drive or via external SDI connections.

In conclusion

As a final word, the explosion in the use of Log modes has led to third parties creating useful sets of LUT presets for popular editing and grading software, including Da Vinci Resolve, Adobe Premiere Pro and Final Cut Pro X. For example, cinematographer James Miller offers a collection of 120 LUTs for a variety of uses here. It has never been easier to take advantage of the huge benefits that Canon Log modes have to offer. They provide much greater shooting flexibility, and the ability to produce just the look you want from your video.