Mobile Camera video footage converted to Log footage

 Mobile Camera video footage converted to Log footage  

fAs digital filmmaking becomes more and more affordable, technologies become increasingly available to colorists or post-production professionals. In this case, Log footage. The Log (logarithmic) color space has been around for quite a while. Initially, high-end post houses used it with scanned film negatives in a color space called Cineon Log. Now, pretty much all camera manufacturers offer their own Log curve (or multiple). There is S-Log 2&3 (Sony), LogC (Arri), Canon Log, V-Log (Panasonic), Red Logfilm, Blackmagic Log, etc. Each of them is different, usually tailored for the color science of the particular manufacturer’s products.

The biggest reason to use the Log color curve is how it retains the most dynamic range of information from the camera sensor (or film negative). It encodes what the camera sees logarithmically, meaning that the correlation between the exposure of the image (measured in stops) and the recorded image is completely constant over a wider range. It utilizes more of the sensor’s information than a standard video curve because it’s saving as much data as possible rather than capturing specifically for the human eye or a video screen. This gives you much more color data to work within post-production.

A CG Element in Linear color space on a Log background.

So, how does Log fit into a VFX workflow?

If you’re receiving Log footage to composite, more often than not, you’re going to want to leave the entire image of the final composition in a Log color space so that it will get color corrected along with the other footage and maximize its data. This can be a problem because, generally speaking, your CGI or video elements are going to be in a more linear color space, like sRGB, Rec. 709 (video), or linear. So you have to convert your elements to Log. We’re going to use a Rec. 709 color space (a color space created for televisions and computer monitors — usually the alternative to Log in digital cameras). Rec. 709 isn’t a completely linear color space, but it’s much closer to linear than Log.

In the example above, the CGI chess set (a model from the starter pack that comes with Video Copilot Element 3d) starts out much darker with higher contrast than the background plate. This is because the footage plate was shot in Log, and the CGI element is in a more linear color space. How do you change the color space of your CGI element? You use a LUT.

A LUT (look-up-table) is essentially a color preset that you can apply to any video footage or element. LUTs create a stylized look, feel, or tone for an image, but there are also a general utility and conversion LUTs. You can use these to change from one color space to another. IWLTBAP has a great free pack of conversion LUTS — check them out here.