Editing
Scoping Out Your Video

Morgan Paar
October 2008

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I recently took a documentary I was editing on a 24" iMac and brought it to a Mac Pro tower with dual 17" NEC monitors and - holy hue! - the colors were completely different. The iMac was much more vibrant, but were those the true colors or just a slick Apple monitor? How do we know what true colors really look like?

The videoscopes in higher-end video editing software programs such as Final Cut Pro, Premiere Pro or Avid systems are very similar to their physical hardware cousins in online or color-correction facilities. They provide exact measurements of color, including its hue, saturation and luma levels (explanations below). When we deal with these scopes in post production, we are using them to help us match shots, to correct individual shots, to make our overall videos more consistent or for special effects. We can use scopes on set to adjust the image the camera is capturing, which, of course, would make our job as editors easier, or even while capturing, though this is not always economical in our no-budget world. So most of the time we're forced to "fix it in post."

Today we will be talking about four scopes: the Waveform Monitor, the Vectorscope, the Histogram and the RGB Parade. But first, a quick primer on what exactly we are measuring.

It would be a wonderful world if we measured our colors in video editing only in the RGB mode. In this system, all the colors we perceive are some combination of red, green and blue. In the RGB mode, all three colors contribute to the perception of brightness as well. But this simple mode became a problem in the early 1950s, when engineers were trying to figure out a way to switch from black-and-white televisions to color, while still leaving the b/w sets relevant.

To make a long, technical explanation simple: television engineers developed a way to make a solo luminance channel. This regulated the light intensity as seen by humans, which existing b/w televisions could decode. Color sets received the same luma channel but also received two additional color channels that could be decoded back into RGB color. Humans are more sensitive to luminance than to color fidelity, so the engineers developed a system that reduces color information in the compression of images, limiting the amount of data needed to reconstruct an image.

The first part of our image consists of light or luminance or luma. This is the brightness of the video, from absolute black to the brightest white, including all shades of gray in between. We can measure luma in different ways (8-bit RGB data is typically measured from 0 to 255), but some editing systems measure it with 0 equaling absolute black and 100 being absolute white. Many editing programs and cameras will surpass absolute white into super-white. It is important to know that, even though your camera may record luma levels into super-white and your editing software can deal with that, they are not broadcast-safe.

Chroma is color and consists of two parts: hue and saturation. Hue is the color itself - red, green or blue, for example. Saturation, as its name implies, refers to the intensity of the color, such as dark blue or a faded, light blue.

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