Colour charts are a huge help on any shoot. In a world of ever changing cameras, sensors, colour spaces and gamma curves, the humble colour chart is a talisman of consistency and reliability. It’s whole reason for existing is to stay the same, to never change and, therefore, to always give you a definitive reference for colour. So if you want to quickly get a balanced and accurate look to your shots, across multiple, mixed cameras and picture profiles, a colour chart is a must.
So, you’ve bought your colour chart…now what! There is a tad more to it than simply holding it in frame and then forgetting about it. For starters, they normally come with an 18% grey side that you can white balance your camera with. For most cameras, that is a case of pointing the camera at the grey card and pressing the custom white balance button. However, in most cases, the camera has to be close enough to the grey target for it to fill the frame or at the very least be large enough in the frame for the camera to take a decent sample. What people tend to do, then, is move the chart towards the camera, as that is a hell of a lot easier to do than picking your entire rig up and walking it in. The problem with that, though, is that the light then falling on your chart is probably quite different to the light falling on your subject, therefore completely negating the purpose of what you’re trying to achieve – a balanced subject. For this reason, you want your chart to be where your subject is, often holding it right in front of their face (if it’s an interview, for example). As I show in this tutorial video, using a monitor (that supports RGB parade or RGB overlay waveforms, such as the SmallHD range that I use) your chart can be relatively small in the frame, where your subject is and you can still get an accurate white balance. In the case of the parade, you would simply make sure the traces that represent your chart in the three waveforms are all at exactly the same height. In the case of the overlay, the traces would overlap, causing them to appear white on your scope.
As I discuss in the video, having a balanced image in camera is of paramount importance. Even if you’re thinking you may go for a certain colour look in the grade, give yourself a balanced shot first, and work from there. The vast majority of codecs throw away tonnes of colour information, so making substantial changes in post, just to get a balanced starting point, will unduly stretch your signal and risk creating nasty artefacts in your footage. Get that bit right in camera and then you can make the most of whatever colour information your codec has retained in post.
Next up, get the colour chips of your chart in shot and record a few seconds. Either there and then, on set, or further down the line when your edit is locked, you or you DIT/colourist can very quickly (takes me about 3 minutes per chart) use a vectorscope to line up the chips with their corresponding boxes. Using the curves, (specifically the Hue vs Hue and Hue vs Sat controls) inside DaVinci Resolve, you can quickly line up the primary and secondary colour chips of your chart with the corresponding boxes on the vectorscope. Now, there are all kinds of broadcast based conventions in place that govern what is and isn’t safe to transmit but, as everything I ever produce goes out online, I must admit, I take a lot of those rules with a pinch of salt. I often stick two fingers up to title safe boundaries, wilfully allow the odd highlight to go above 100 IRE and don’t always stick the saturation values of my colour chips dead centre in their boxes on the vectorscope. The truth is that the rules that govern these things for broadcast simply don’t apply to the viewing platforms my clients use, which include tablets, smartphones, laptops and PCs. In particular, I find most phones and tablets are factory tuned to be more saturated than you might expect. Therefore, I tend to allow the saturation of my chips to just fall on the boxes in the vectorscope. The key thing is that they are equal, with no one hue being more saturated than another at this stage. This is, after all, a primary grade (or base grade) and, as such, I am simply looking for consistency and neutrality at this point.
So, that’s why and how I use my Xrite Colorchecker Video. If you want colour accuracy across all your cameras and all your shots, simple tools and procedures like this can make a world of difference.