If you’re an avid reader of the Adorama Learning Center or any website or trade that lauds the latest high-end video camera, you’ve probably come across the term “log” a lot. For example, you’re into gear porn and salivate over the latest Atomos converter/monitor and how it contains not one, but two recording logs (such as the Canon C-Log or Sony S-Log), and you think “Great! I want THAT! But what does that mean?” To add further confusion, someone might over simplify what the technology does by responding with “a log is a means to record your footage in a specific way, so that you can apply the corresponding LUT (Look Up Table) in post production.”
Okay?
While there is some truth in that generalization, there is a lot more to it (obviously) as it does not tell the whole story. You don’t believe me? Let me throw the Rec. 709 format into the pot and explain what that represents. And then tell me your head will not reel.
The reality: it is pretty simple. However, therein lies a lot of “depends” in terms of whether you use a log or LUT or in how one might relate to the other or not at all.
First, let’s explain what a “Log” is. Think of it as a profile like the kind made available through an HDSLR. Scrolling through the menu of a Canon 5D, for example, you might encounter various profiles allowing you to shoot in monochrome, a cinema-like style (has more contrast and is more color saturated), a profile that highlights certain details when taking a landscape shot and, finally, something mysteriously titled “neutral.” When shooting under this particular profile, the resulting image looks flat, low on contrast and somewhat washed out. This enables the photographer (or videographer) to enhance the image in post. You see, by achieving that low contrast image, you now have the opportunity to bring out more dynamic range hidden within that image. It has been both an old photographer’s and videographer’s trick to shoot that way for that reason. The only problem is, you will not be able to see the resulting image in-camera until the proper color correction is applied – the very process required to bring out that dynamic range.
For those less informed professionals who acquired the first iterations of the Black Magic Cinema camera, they were confounded by how an odd visual would appear on the built-in monitor. It didn’t look rich with color or detail. And that’s because it would automatically feed the image through its own personal profile or “log.” The result was very similar to what one would achieve while shooting with a neutral profile on any number of DSLRs. They just didn’t realize at the time that the BMC camera was, in reality, a post production cam. Fifty percent of the visual would be achieved in camera whereas the other 50% would have to be achieved in post. This was the only way to ensure the widest dynamic range possible once the project was fully edited and completed.
So, depending on whether you’re shooting with a Canon C300, a Red Scarlett, Sony F7 or Arri Alexa, the manufacturers of each camera have developed logs that are specific to each camera, especially those that are built to shoot professional video for television and film. “But why?” you may ask, “does the image have to look flat in the first place?”
This is where we get to the really complicated part. And I’m terrible with science, so bear with me as I try to explain this as quickly and concisely as possible. But when a digital sensor records an image, traditionally it records light linearly. This would create an access of samples? Lines? Whatever you want to call them, there would be an abundance of those “things” within the highlight detail. So much so that the human eye cannot perceive them. Whereas by using a log, those access samples would be eliminated and spread out evenly along the curve; the “curve” being the full gamut from black to white. The steeper part of the curve contains mid-tones, blacks and shadows while the brightness/luminance values are stored where the curve begins to flatten out.
So a log does record the details, it just spreads them out in way that ensures the widest dynamic range. Unfortunately, the human eye cannot see it, yet. That is until a LUT is applied to that recorded footage.
Before I get into what a LUT is, we should establish just what a LUT is actually used for. The LUT (an acronym for “Look Up Table”) was originally conceived to aid in the color grading of analog film. It would act as a mathematical “map” guiding the film conversion process from raw to its final form (using an RGB scale, for example, a LUT would calculate how many reds vs greens vs blues should appear on film).
Later on, a LUT would match the color calibrations of an image shot on film to that of its digitized form, thus making it ready for theatrical projection (and eventual DVD distribution). Since almost everything is shot electronically these days – and projected as such – the LUT now acts more or less as a color grading plugin helping to achieve a more filmic look. LUTs are generally not customizable. You cannot readjust contrast, highlights, or color schemes once one is applied. The only aspect you can change is the intensity of the look the LUT provides.
The importance of a LUT rests in how it brings out the dynamic range information recorded via a log. Add that LUT in post, suddenly the image transforms from washed out, lacking in saturation to a more detailed and saturated form. There exists many kinds of LUTs that can achieve different looks – some have a more “cooler” feel than others – but they all serve the same purpose. And that is to finally show the human eye the rich dynamic range that was imperceptible when viewing log footage before the LUT was applied.
That’s not to say you absolutely have to use a LUT when color grading footage recorded via a log. In fact, you should still color correct the usual way (so the desired look matches from clip to clip) and then apply the LUT. But there is no hard and fast rule on this.
Today’s cameras, and the external monitors attached to them, are now equipped with the ability to view the footage as it would look once the LUT is applied. This does not automatically eliminate the need for applying the LUT in post, however. It simply exists to give the videographer an approximation of how the video feed 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. Using a combination of the Rec. 709 format with whatever log is being used in camera, you will see more saturation and contrast on a monitor than you would without it. However, this only establishes the broadcast standard and not the aesthetic look you were aiming to achieve. At the end of the day, you might use a corresponding LUT for that as well.
As an experiment, you might want to try this. If you’re a budding filmmaker or a photographer making the transition from still to video, chances are you already own a DSLR. Download Technicolor’s Cinestyle package here. Don’t worry: it’s totally free. It comes with a profile and a corresponding LUT. Once you follow the instructions and properly uploaded the profile while installing the LUT, go out and shoot some footage via the Cinestyle setting. This is tantamount to recording video through a log. Then shoot footage normally without the profile. Go home, upload your footage to your computer and place it within a non-linear editing timeline of your choice.
(If you are working with the latest CC version of Premiere, this will be very easy for you as you can call up the Lumetri plugin and apply the LUT from there. If you’re working with an earlier version or Final Cut Pro, download Red Giant’s LUT Buddy plugin and install. Either way, you should be able to access the Cinestyle LUT once everything is ready for edit)
Now look at your raw footage before you apply the LUT. And see what happens afterward. Then compare that result to the footage you shot normally (without the profile). And see if one version has more detailed range than the other. You’ll notice a difference.
