The Log vs the LUT

Last week in our review of the Nikon D850 I said I’d address the topic of Log vs LUT. What is a Log as opposed to a LUT (Look Up Table)?

A simple explanation is that a log is a way to record video in a specific way. Then in post you can apply the corresponding LUT (Look Up Table).

But it’s a bit more complicated than that. A Log is the profile in a DSLR. The profile settings have different values for gamma, black level, color phase and other processing adjustments. In my old Sony EA50 for instance, I can choose a picture profile that renders color tones in standard gamma, cinema negative film, cinema positive film and others. It’s important to see the differences between these profiles before choosing one, but for some cameras this profile is misleading. With the early Black Magic Cinema camera, 50% of the visual would be achieved in camera, but the other 50% would have to be achieved in post. There was no other way to get the widest dynamic range. The footage looks flat until an LUT (Look Up Table) is applied.

The Log

The shot on the right is with the Sony S-Log2 applied. The shot on the left is with no log applied. In the Log shot the shadow detail is retained and can be brought out with a LUT. In the shot with no log, the shadow detail would be lost.

Log is short for Logarithm. Manufacturers have developed logs that are specific to each camera they produce for professional video. These days log footage has also become available in many consumer cameras. Log footage typically looks flat. It only comes to life when a Look Up Table (LUT) is applied in post. The log does record the details, but it spreads them out in a way to ensure the widest shadow detail and dynamic range. At this point the Log footage looks washed out. The human eye cannot yet see that range until a LUT is applied.

A LUT is a mathematical map which guides the video from raw to its final look. It calculates, for instance, how many reds vs greens vs blue will appear in the video footage. A LUT acts like a color grading plugin to achieve a more filmic look. Generally a LUT cannot be customized. The contrast, highlights, or color schemes are locked. The only thing that can be changed in a LUT is the intensity.

The LUT brings out the dynamic range information that was recorded through the log. So the footage that looked flat now looks saturated and detailed when the LUT is applied. Some LUTS have a cooler look, but they all show the human eye the rich dynamic range that was not visible when viewing log footage before the LUT was applied.

Many cameras and external monitors now have the ability to view the footage as it would look when the LUT is applied. But the LUT is still required in post to get that look. This gives the camera operator an idea of how the video could look in post. This should not be confused with the Rec. 709, which is not a log but an industry established format for HDTV broadcast.

Here’s an experiment to try. Download Technicolor’s free Cinestyle package. It includes a profile with a corresponding LUT. Follow the instructions to upload the profile and install the LUT. Then shoot some footage via the Cinestyle setting. This is like recording video through a log. Then shoot footage without the profile.

Bring the footage into your non-linear editor. Look at your raw footage before you apply the LUT. Compare it to the footage with the LUT. See the difference in range and detail.

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