Secondary Color Correction

4 minute read

A very important part of creating the artistic look of your film is drawing the viewer’s eyes to particular aspects of an image (faces, props, logos, and lots of other things). Now, of course, much of this work is achieved by the DP during shooting. Shots are framed in camera so that the most important elements of a scene are prominent, while less important elements fall into place around it. But sometimes you’ll need to alter an image even more precisely than pure cinematographic techniques can achieve. This is where secondary color correction comes into play.

Secondary color correction is the process of manipulating specific parts of an image. Unlike primary color correction where every pixel on screen is affected by the changes, secondary correction only adjusts certain area within a shot.

There is a multitude of tutorials online that use secondary color correction to radically change the color of someone’s clothing, or perhaps completely redo the color of a set/environment. However, in most cases, secondary color correction is used to much subtler effect.

One of the biggest uses of secondary color correction is to adjust skin tones, and other colors that humans have a common familiarity with (like natural colors in foliage and the sky). These colors are often less than perfect after a round of primary color correction. After all, primary tools are most concerned with getting the majority of the image where it needs to be. But that can be to the detriment of specific parts of an image. So, secondary tools help you finesse those colors to look just right.

But other than simply “fixing” what primary correction leaves out, secondary correction enables you to hone a shot for specific purposes of the story. Want to build tension over a particular part of the screen? Darken everything around that area, so that it ominously stands out. Need a character to feel a bit happier? Add a subtle glow around their face. The potential to use secondary tools to craft the look and feel of a scene are almost limitless.

Making Secondary Corrections

To make a secondary correction, you must first isolate the part of the image you want to adjust. There are three ways you can do that.

The first method is to select pixels based on their value. This value is usually a specific Hue, Saturation or Lightness (or combination of all three), a process known as HSL secondaries. To use this tool, you set a range of qualifiers. Qualifiers are usually in the form of slider bars, where you set two points along the line, and the values within those points are the selection. In essence, this selection is a mask defined by HSL color values.

HSL Secondaries are essentially the same as Keyers, which we will cover in more detail in the VFX section.

The second method to isolate part of your image is to select pixels based on their position in the frame. The tool for this is often called a “power window” but you can just think of it as a spatial mask. These selections are drawn on the screen by the colorist around the pixels they want to manipulate. Most often, these are just simple geometric shapes like circles, ovals, or rectangles, but they can also be complex shapes that completely encompass particular set pieces or characters.

The third method is to select pixels based on a combination of their values and position. This is very useful when neither of the above methods is quite precise enough in selecting the exact pixels that need to be adjusted. Heavy color work will chose this method most often.

For instance, it’s common to want to select and change just a character’s skin tones, and an HSL secondary is a great way of doing that. In some cases, however, there may be other objects (perhaps a cream-colored wall) that are almost the same color. An HSL secondary would affect both the skin and the wall. Adding a power window around the character could prevent the correction from touching the wall as well.

Keep in mind that there are tradeoffs to each of these methods. Selecting pixels based on value qualifiers is fast, and doesn’t require any motion tracking to maintain the mask, but is often less precise. Selecting pixels based on their position is more precise, but often requires motion tracking, which can be slow. The third method of combining value and position is the most precise, but takes the longest. You will likely use all three methods when coloring your film. But it will just depend on the shot.

One you have your selection, you can adjust all of the properties of the pixels within it using the tools we learned before, like color wheels and curves. Pretty much anything that you can do to color in primary correction, you can do to just the isolated parts of your image in secondary correction.

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