The first thing I look for when browsing the raw media coming from a client prior to a color grade is the quality of the skin tones. Skin tones will tell you most of what you need to know when assessing the technical quality of a digital negative. Exposure, white balance, tint, mid-tones, saturation, noise level, black saturation, and even sharpness. I use the same approach whether I’m referencing from a calibrated viewing monitor on set or in the color suite during the finishing process. If I were to break down the amount of time I spend as a colorist working with a particular shot, you would see that I spend a significant amount of time working on skin. For a number of reasons, I’ve decided that good skin tones are my line in the sand.
Skin Tone: A History
The diaspora of humanity out of the African continent over the last 50,000 years has led to some of the most fascinating evolutionary adaptations. In fact, we wear our direct connection to mother Earth on the surface of our skin every day. As people began to fan out across the curvature of the globe further from their origin point of sub-Saharan Africa, they were also decreasing the angle of incidence from the sun’s radiance. In other words, the further they were from the equator, the less direct sunlight they received. Our African ancestors had evolved a natural protection against the sun’s harmful UV radiation by producing a chemical in the skin called melanin. Melanin is mother nature’s sun screen! The disadvantage of melanin for someone who lives further from the equator, is that their bodies no longer receive enough sunlight to produce vitamin D. So, over thousands of generations, Northern peoples began to select for lighter skin in order to maximize efficiency. When we burn in the sun, a tan is our body’s natural way of producing melanin in order to protect itself from UV radiation. These varying shades of skin color are the visual representation of human tenacity and our direct relationship with our planets geography and our nearest star.
Here we are thousands of years later and humanity is represented by a continuum of shades of a similar color spread out across every corner of the globe. Regardless of the specific hue of our skin, we all share the exact same color of blood. Blood and melanin together produce a sort of pink-ish / orange-ish “skin tone” that vacillates moment to moment depending on a number of parameters including but not limited to: incident light, ambient temperature, health, and emotional state. Skin tone is a bit of a broad term, but a helpful start when discussing the topic with a colorist. There’s no such thing as the perfect skin tone. Every lighting situation, camera technology, and LUT is unique and dependent upon the needs of a given scene and the limitations of the capture methodology. However, simply having a good grasp of the concept and knowing the tools and techniques you can use to approximate healthy looking skin is all that anyone can ask of you. Hopefully this article will help you dial in your skin tones with finer detail and more confidence.
Our primary focus when we see a photograph or the moving image for the first time is the human face. We’re programmed that way. Or rather, we’ve evolved a particular fascination with faces as they are our primary interface for multi-modal interpersonal communication. Beyond oral communication, faces morph and contort into various shapes in order to convey more complex emotions and language. However, our faces also transmit more subtle and subconscious information in the form of color that we often use to determine each other’s emotional state as well as physical and mental well-being. Over the millions of years of evolution that it took for us to get to YouTube and HBO, our ancestors and their ability to transmit and receive critical information via the hue and saturation of their epidermis has now become an important part of our experience in viewing the digital image. We have been imbued with the superpower of color sensitivity that falls within the specific range of human skin color and we can use this amazing ability to guide us when having to make arbitrary decisions with color balance and exposure on set and in the color suite.
Your Camera and It’s Color Science
The digital cameras that we use in the film and television industry are designed to capture information using red, green, and blue channels. Digital camera sensors are manufactured using a variety of precious metals and other materials like silicon and each have their own technical limitations. One significant characteristic to a sensor is it’s spectral response. This is essentially a sensor’s specific sensitivity to red, green, and blue and how it represents this color information in the bit stream. In short, different sensors see colors in different ways. Every sensor manufacturer has its own secret recipe to how it captures light and color information based on a cornucopia of patents and workarounds.
I use the term “workarounds” as a more polite way of saying trickery. As I detailed in our recent article Video Noise and the Origins of Our Universe, sleight of hand is the name of the game when it comes to the digital representation of human perception. When a company like Sony is making a sensor, their design specs cannot be drawn outside of the constraints of their patents. Sony has a specific methodology and corresponding intellectual property to its own image capture strategy. Capturing color information with the current technological method (RGB pixels on a silicon sensor) has a lot of technical challenges, namely, spectral response limitations (color interpretation). Sony engineers and imaging technicians in their lab have to tweak a lot of the input values coming off of the sensor before encoding to an RGB data stream for the image to actually look objectively accurate. Even under laboratory conditions, a properly exposed and white balanced camera will display some odd characteristics to common objects like skin and clothing. Our goal as imaging professionals is to understand objective image control and how we can use this to our advantage.
Pro Tips for Better Skin Tones
Before buying or renting a camera to shoot your next film, understand what the limitations and advantages are that will affect skin tones. Arri and Canon have strong reputations with regards to skin color and color science in general, however, they both have a difficult time in low light. Sony cameras are competitively priced, have a gazillion bells and whistles, and have been engineered to practically see in the dark. However, I’ve always had difficulty pulling good skin tones out of their negs. In our previous post, Why You Should Talk With a Colorist Before Shooting Your Documentary, I encourage you and your team to take the time to do some camera tests prior to principle photography. There are also a plethora of videos online that compare camera models and their reproduction of healthy skin tones. Just keep in mind that when it comes to the color grade in post, your colorist will likely bill more hours depending on how good or bad your skin tones are!
Get it Right On Set
I’m going to use a hypothetical situation which involves a documentary filmmaker shooting with an industry standard digital cinema camera in a real-world situation. Let’s say you’re shooting a film in someone’s home and there are different rooms with various lighting qualities. You may also have a few interviews in fixed locations. You might be shooting with a Canon C300 or a Sony FS7. Since you’re shooting a doc, you’re most likely recording to a compressed format like I-frame AVC or HEVC. Hopefully you’re able to choose a 10-bit 4:2:2 recording option for 4k, but there’s a chance that you’re recording within an 8-bit 4:2:0 stream (as of early 2020). I call this a “thin” codec, and it’s particularly frustrating to work with in the color lab later on. If you have to record in this format, you’ll need to be extra vigilant with your color balance and exposure as the margin for error is significantly more narrow compared with higher bit depths. Low bit depth video is like looking at a sharp blade edge-ways. When your color balance is spot on, the image can be beautiful, however, your ability to represent or recover good color accuracy, and thus good skin tones, diminishes rapidly as you deviate from that optimal center line of balance. The majority of cinema cameras that are currently on the market do not offer a 4k recording option that includes 10-bit 4:2:2 color without upgrades or external recording options. Panasonic is one brand in particular that has provided 10-bit color depth in nearly all of its cinema cameras without requiring any pricey upgrades or add-ons.
Get in the habit of always white balancing your camera for the given scene. I also recommend recording a few frames of a white or gray card or even a color chart when doing interviews. This way, your colorist can dial in the white balance in finer detail later in the lab. When you’re shooting in a scene where there is a mixture of lighting sources of various temperatures, try to get an average white balance of the scene. Recording a gray card and panning it across the scene so that your colorist can later pick and choose a white balance is even better. Good white balance practice is the number one habit that you can form that will generate the best quality skin tones for your film.
Make sure that you’re using the LUT provided by the manufacturer of the camera that you’re shooting with. If you’re shooting in a log format like S-Log or Canon Log, chances are that you’re also using a color science like Sony’s S-Gamut or Canon’s Cine Gamut. These large color spaces are helpful for accurate color reproduction but they need to be translated correctly when coming back down to a smaller color space like Rec.709 upon export. Squeezing a large color matrix down to a smaller box can distort and omit important color information that often results in wonky skin tones. The camera engineers and technicians that design and develop the camera that you plan to shoot with will have created a specific 3D LUT that you can download for free. This is a lab developed LUT that offers the correct translation between a larger cinema gamut and the “crushed” Rec.709 that people often start with in the edit room. This will get you most of the way there with your skin tones!
Color Science Workflow
I find that it’s helpful to visualize the color science workflow of your entire process in order to ensure predictable results that are closer to your original vision from conception. I always document the master camera settings like color science and gamma before starting the shoot. I also make sure that all of the software that I use throughout the post production pipeline always compliments the color science of the capture format until you’re ready to export for final delivery. I recommend referencing our previous article Why You Should Talk With a Colorist Before Shooting Your Documentary as a guide to the discussion you should have with your post production team when strategizing about your color science workflow.
Below is a cheat sheet for a standard documentary color science workflow. Your DP and or Colorist can help you fill in the finer details for each of the modules in the diagram.
What’s Your Vector Victor?
You might have noticed that much of the tips and discussion in this article rely on subjective experience and indirect tools to dial in good skin tones, however, there is one scientific instrument that you can usually rely on. The vectorscope! It’s found in just about every NLE on the market and it’s easy to use. The vectorscope is a circular GUI instrument, or graticule, used to measure and display the hue and saturation of a given image. The incoming video signal is translated into an abstract display of hue and chroma (or saturation) called a trace. If a certain hue is dominant in your video frame, you will see the trace bias toward that specific hue’s target point on the graticule. The more saturated a given hue is in your image, the further outward from the center of the graticule it will radiate.
The three primary and three secondary colors represented on a vectorscope are Red, Green, Blue and Magenta, Cyan, Yellow respectively. Below is an example of a standard vectorscope graticule:
One powerful option with modern vectorscopes is the skin tone indicator that can be turned on and off within your NLE or color grading interface. This line lies between the yellow and red target points and conveniently indicates where a real-world representation of healthy skin would land on a vectorscope. As an example, I’ve presented a few screen grabs and their corresponding vectorscopes from a recent color grade that Magic Lantern did for WeTransfer called Row Houses (Dir. Ingela Travers-Hayward – Debreslay Films):
By windowing down the image using a garbage matte or power window in order to elliminate everything else in the frame except the face of the woman on the right, we can get a much more accurate analysis of the hue of her skin:
Now that I’ve created a matte/power window that focuses just on the woman’s skin, I can then reference the vectorscope and see how close the hue comes to the skin tone indicator. This is pretty much spot on, however, I can see that it is leaning a tad bit into the yellow. This is fine, as I know that the film stock emulator that I’m using tends to bias toward warmer tones. One other note that you should keep in mind is that sometimes the environment will cast a certain color onto the skin of people on screen. In this particular case, there are a lot of beautiful green trees with dappled direct summer sunlight. This could have the effect of a slight greenish cast on the woman’s skin which pushes her skin a little toward the yellow.
Below I’ve added the before and after images of a frame from the same documentary which had a white balance issue. These examples are just to give you a sense of how the vectorscope visualizes two different chromatic representations of the same frame.
As you can see in the frame and corresponding vectorscope above, the trace is skewing heavily toward the blue/cyan quadrant within the reticule.
If you would like a more detailed tutorial on how to use the vectorscope, specifically in Premiere Pro, you might want to visit Andrew Devis’ article on Premium Beat. For more information on some of the other scopes you’ll likely have within your NLE, Jarle Leirpoll’s Frame.io article on the four primary video scopes is an easy-to-read breadown with visual aids.
At some point in my career as a documentary DP, I realized that I was moving too fast. The more I slowed down and shot for post, the more rewarding my photography became. Deliberate technical choices will eventually become muscle memory and you will improve over time. Slow is smooth and smooth is fast. Take your time, white balance your camera for each scene, document your settings, and enjoy the pleasure of seeing good skin tones. And remember, we’re all simply different shades of the same hue!