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Day 24: 25 Insights in 25 Days Holiday Marathon
Why is Camera Matching with Color Charts So Hard?
In Resolve 11, Blackmagic released a heavily hyped new feature: Automatic Color Match. From their website:
Simply use the chip grid to identify the color chip chart and Resolve will automatically balance the images, even if they were shot on different cameras, under different lighting conditions and with different color temperatures!
The promise is simple, shoot a color chart and have your Primary Corrections set with technical precision and all your different cameras matching each other.
Whatโs the problem?
The problem is: Automatic Color Match rarely matches
The intertubes are littered with forum and blog posts of professionals who have been taking the Marketing copy at its wordโฆ and are finding it sorely lacking.
In fact, many pros are finding it so frustrating they no longer trust the tool.
If you donโt trust the tool, you stop using it
In this short series weโre going to first frame the problem: Why is the Automatic Color Match tool not working the way editors, DPs and colorists want it work?
Then weโre going to help you figure out a workflow that is repeatable and workable.
Automatic Color Match works if you use it properlyโฆ
But whatโs the proper use of Automatic Color Match? The manual has a few things to say about it, but nothing that solves the problems that seem to be plaguing people.
What we need to do is more precisely define the problem that Automatic Color Match is trying to solve. Then we need to test to see what the tool is actually doing.
And then, finally, we need to develop a workflow that bridges between our expectations of the tool and the reality of how it works (weโll tackle this in the final part of this series).
Special Thanks to MixingLight Member Greg Greenhaw!
Over in our series on working in LAB Colorspace, Greg offered to shoot me a test scene with a color chart (with a Blackmagic 4K camera).
Since I rarely ever see color charts in my professional work, I jumped on the opportunity to work with his footage. Whatโs even better โ he mistakenly first shot his test scene to Rec. 709, not to BMDFilm (a flat, log-profile image). He then re-shot the scene to BMDFilm and provided me both files. This turned out to be the Perfect Camera Matching Test โข.
We start by matching the same camera to itself
Since Greg provided both the Rec 709 recording and the BMDFilm recording of the exact same scene with the exact same camera using the exact same lensโฆ we can remove those variables from our experiments and figure out how to get Resolveโs Auto Color Match tool to work.
We refine using the DSC Labs SMPTE OneShot
At the time of this writing, DaVinci Resolve supports four different color charts for automated shot matching, Gregโs test image included two of them! He gave us the X-Rite Color Checker and the DSC LABS SMPTE OneShot.
In this series, Iโll be using the OneShot for evaluating this tool. Why?
The OneShot is based off the work and ideas of Cinematographer Art Adams. And Art has a great article on how he designed the OneShot, with a full explanation of exactly the targets he designed the chart for andโmost importantโhow the chart is designed to be used.
Using Artโs explanation of the OneShot, we can deconstruct Resolveโs Auto Color Match feature
While reading how Art uses the OneShot, I had an Ah-HA moment of my own when he said this:
Itโs more important to ensure the colors fall on the correct โvectorsโ, which are lines drawn from the center of the vectorscope through each color box. If the colors fall on the proper vectors they are at least accurate, even if they arenโt fully saturated.
This is the key to understanding how to properly use a color chart โ and what precisely Resolveโs Auto Color Match feature is doing to our images.
What youโll learn in this Insightโฆ
By the end of this Insight, you should be up to speed on how to define the problem weโre all having when camera matching with color charts.
In the next partโฆ Iโll offer up a workflow solution for getting much more consistent camera matching results.
Other Resources
A lot has been written on using color charts. Iโve pulled a few URLs that I thought you might find interesting:
โข Art Adams: Rough Guide to Color Grading with the DSC Labs SMPTE OneShot โ The man who designed this chart takes it out into the field to share his thoughts on how to color grade.
โข Curtis Judd: Resolveโs Auto Color Match โ This YouTube video has some good things to say about different light sources. Plus youโll get a good idea how to use the Color Match feature.
โข Blackmagic Forum: Recommended Color Chart for DaVinci Resolve? โ A forum thread with lots of interesting advice, reflections and thoughts on how and when color charts are useful to a colorist.
โ pat
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