To match the cameras, choose the gamma curve option that matches best. Then adjust black level (aka master pedestal) and black gamma (aka black stretch) to change the lower end of your contrast curve. Adjust knee point and slope to change the upper end of your contrast curve. Matching the gamma curve of two cameras can be difficult to do, and you may choose to use a Hyper or Film-like gamma on your more adjustable camera to better hold highlights. If this is the case, just try to adjust black levels, as they have the most obvious effect on color.
INTO THE MATRIX
Now that we’ve matched exposure and gamma, we can dive right into color matching. It’s very important to have a vectorscope of some kind for this step. A vectorscope visualizes hue and saturation, where the distance from the center of the scope shows saturation and hue is represented by location on the scope. Using this tool, we can quickly adjust the match camera’s saturation to be similar to the hero camera. Hue also can be adjusted, but a little adjustment here goes a long way. Once saturation is generally the same, we can further refine our match by using something called the matrix.Many professional Panasonic, Sony and Canon cameras come with matrix presets and adjustments. Matrix presets are color adjustments predefined in the camera, and flipping through available matrix presets may get you pretty close to a match. Beyond that, many cameras give you six matrix adjustment options: R-G, R-B, B-R, B-G, G-R and G-B. These adjustments adjust how red, green and blue channels from the camera sensor mix together. Color is made in a digital camera using a prism (in the case of a 3CCD or 3CMOS sensor) or a color filter array (in the case of a single-sensor camera). Both technologies produce red, green and blue images in the camera. The matrix adjustments allow us to adjust how these three images mix together. For instance, the R-G adjustment will subtract or add (with a negative value) the green channel from the red. Removing green from the red channel produces more saturated red colors, but green colors will change both in hue and in saturation.
It seems a bit confusing, I know, but here’s a simple rule of thumb. When adjusting any one of these combinations, the first color (R, G or B) will be affected in saturation and the second color (R, G or B) will be affected in both hue and saturation. When matching cameras, these adjustments can really get the look of two cameras very close together. Be sure to pay special attention to skin tone during this procedure, though, as we tend to notice skin tone differences much more than other colors.
Beyond the matrix, some cameras offer something called a Multi-Matrix or Color Corrector. This option allows you to change the hue or saturation of a specific color range. I don’t generally adjust these for a match unless two cameras need a specific color to be exactly the same.
So now we have matched exposure, white balance, gamma and color to get our two cameras lined up. The next step is to change the lighting situation and see how the two cameras perform under different circumstances. You may find that under daylight the cameras respond differently, and the only way to know is to test them. I recommend keeping saturation of color fairly moderate on both the hero and match cameras to help avoid potential problems.
An exact camera match can be difficult or even impossible to achieve, but if this process can speed up the post grading process, then we’ve gained a lot. I was able to make a scene file for my client that matched the F3 to the FS700U pretty closely. However, after discussing it further, they opted for a look that had colors similar to the FS700U, but with a special gamma mode found in the F3 that gives it more dynamic range. They didn’t want to sacrifice the quality of the F3 for a match. Keep this in mind as you make your own scene files. Happy matching!
Andy Shipsides is a N.Y.-based Camera Technology Specialist and Manager of AbelCine’s Training Department. To learn more about AbelCine’s Understanding HD Series, visit training.abelcine.com.