3 Different Ways to Convert LOG Footage - Tutorial
How to Convert LOG Footage to Rec.709
In this tutorial, we take a look at 3 Different Ways To convert LOG Footage to REC. 709.
Log footage can be tricky to deal with if you're unfamiliar with working with it and so here are 3 different ways you can convert it to REC. 709 to make your life easier when it comes to grading.
Let's take a look at three different ways to covert log footage to Rec. 709.
The workflow for each version of log is slightly different, however, these three methods can be transferable to any variation that you are using, whether that be, Arri, Canon, or Sony for example.
Shooting in log is great for maintaining the dynamic range of your camera, but it can be a bit tricky to work with when it comes to colour grading, if you're not familiar with the conversion process.
Converting my footage from log to Rec. 709 is always my first step when it comes to grading.
The first method is only available in DaVinci Resolve as far as I'm aware, however, the second and third method can be used no matter what software you are using.
First, We'll take a look at color space transform. This can be found in the Open FX menu in DaVinci resolve.
As the name suggests, color space transform will convert one color space to another.
Once you drag it onto your footage, it will give you several options.
I'm using S-Log2 and so I will choose the appropriate settings. S-Log can be more difficult to work with than other log formats as it is often exposed to the right.
My Input Color Space will be S-Gamut, my Gamma is Sony S-Log2,
and I want the Output Color Space to be Rec. 709, and the same for my Output Gamma Rec. 709
There are a couple of things to take into consideration here.
If you are going to do further grading, you will want to leave tone mapping and Gamut mapping set to none.
If this is the final step you may want to consider, enabling luminance mapping and saturation mapping as these options will make your levels within legal range and brings colors that fall outside of the working color space back within range.
If you have exposed to the right with S-Log, you can use contrast and pivot to edit your image to within range.
The second method we're going to take a look at is with the help of a color checker, such as this one from X-rite.
This chart has been designed with Rec. 709 in mind and so it can not only help you get your log footage within range, but it can also help with exposure, skin tones and white balance.
I've talked about this chart before and if you'd like to hear more information about it, you can watch that video here:
There is an automatic feature with most NLEs to work with charts like this, however, I prefer to do it manually to get more accurate results.
I'm using power windows in resolve, but this can be done with masks in Premiere or Final Cut.
The first step is to create a power window around the exposure chips and then checking the waveform, you can then manually set your black and white points.
The next step is to then adjust the power window to cover the saturated color chips. Using the hue vs hue and the hue vs sat controls, you can manually adjust them until they appear correct on the Vectorscope.
Your log footage should now be within the Rec. 709 range and you can continue with your grade from here. If you are filming a lot of shots in the same situation, you could export this look as a LUT, which will save you time in the future.
This brings us onto the final method we're going to look at in this video, using technical conversion LUTs.
These LUTs are different from your look or show LUTs that produce a more stylised look.
These LUTs may be the easiest way to convert your log footage to REC. 709, however, this comes with some downsides.
LUTs are destructive, and so any additional grading you do after a transform LUT is applied, will be limited. Any information that is clipped, will no longer be available.
LUTs are also generic, meaning they will not work the same for everyone. You will still need to make adjustments.
The best method when working with LUTs is to always have a pre-LUT layer or node to bring back any clipped information. I also prefer to do my REC. 709 conversion at the start and then do the rest of my grade. This is useful when working with qualifiers for skin tones as you are no longer working with log footage.
This kind of LUT is known as an Input LUT.
While this method may be quicker than the previous methods, it is also the most limiting so that is worth taking into consideration.