Human eyes are not reliable tools for assessing color. Scopes, on the other hand, give you accurate information every time.
Scopes are easily among the most important tools for anyone working with images or video. Because human eyes are unreliable for accurately assessing color (because the brain adjusts the visual feed based on surroundings — not to mention that no two screens are exactly the same), scopes provide accurate information about color and exposure levels, so you can ensure that your footage looks great on any screen.
In this article, we’ll take a look at the four major scopes, including how they work and when to use each one.
Understanding Your Scopes
First, for our exploration of scopes, we’ll be using Premiere Pro’s built-in Lumetri Scopes. Scopes vary slightly across applications, but the foundations of each will always be the same.
While scopes look intimidating, it’s helpful to remember that they are just complicated, specialized graphs. The four main scopes are simply bar or pie graphs that plot data points in various ways, depending on the intended use of the scope.
One quick note: if your computer is beefy enough, always make sure to turn off “Clamp Signal,” and set the color space to “Float.” These two settings will ensure that all of the information in your shot gets represented accurately in your scopes.
Histogram
The most commonly used scope is the histogram. Any modern prosumer or professional video camera, DSLR, or external recording device likely has a built-in histogram. The histogram’s prevalence makes the ability to read one an essential skill.
In Premiere, the Histogram is rotated 90 degrees from its usual orientation. This helps you more clearly visualize the information — the top of the scope represents the highlights in your image, and the bottom represents your shadows.
Every histogram breaks down into 256 sections, representing each Luminance (Y) value in Rec.709. The histogram analyzes the frame and evaluates the total number of pixels reporting that Y value, and it plots each pixel at the proper point on the scope.
A well-exposed histogram should typically look like a bell curve with the majority of the pixels falling in the comfortable mids, with soft gradation into the shadows and highlights. The “center” of the curve may move up or down depending on the light levels in the shot, but as a rule, keep an eye out for heavy clumping of tones toward your shadows and highlights. (This will save you some headache down the road.)
Color overlays on the histogram aren’t especially useful because you’re only seeing a representation of how bright your colors are. Sure, that can be helpful information, but we’ll get to the best tool for color measurement shortly.
For now, let’s look at another scope for exposure.
Waveform Monitor
The Waveform Monitor is, in many cases, a direct upgrade to the histogram. While it displays similar information, the Waveform graph provides additional information that makes bringing your shot into proper exposure much simpler.
The Waveform Monitor takes each single-pixel horizontal slice of your frame (so 1,920 for HD) and plots each vertical pixel according to its gray level (or luminance value). As a result, the waveform offers significantly more control and versatility over the histogram because you can visually locate bright and dark areas in your shot.
Proper exposure on the waveform should show a large spread between the pixels in your frame, while improper exposure will lead to clustering of the dots. Any information that falls above or below the graph ends up clipped and could result in your video being rejected.
Most waveform monitors also have color overlays that you can enable, but again, there is a better tool for the job. One way the RGB waveform can be extremely useful, however, is when you’re getting unwanted color tinges in any part of your image. When you enable the RGB and Luma overlays, you can see where the undesired color tint is. Simply bring the color down, or the others up — when your colors are in balance, the dots will turn white in the scope.
With the two main scopes for exposure covered, let’s dive into the color scopes.
RGB Parade
The RGB Parade functions similarly to the waveform with corresponding horizontal pixel location and vertical pixel brightness, but instead of overlaying each color channel, they are separated into three distinct waveforms.
You can read the RGB Parade exactly as you would the waveform monitor, with the top and the bottom representing the highlights and shadows, and with the left-to-right axis being the location in the frame.
For color work, the Parade is especially simple and useful. All you need to do is use each color in the parade to evaluate your shot (e.g. Is there too much green in the highlights?). Your scope should confirm your intuition with clusters of green dots peaking at higher levels than red or blue. To balance your highlights, simply navigate to the Curves Panel in Lumetri and adjust the top point of the green curve to bring the peaking greens into balance with the reds and blues.
Quick and easy, the RGB Parade is invaluable for speedy color balancing — especially when you use it with color curves.
Vector Scope
And lastly, the king of color monitors: the Vector Scope.
The vector scope lays out the color information in the shot across a color wheel. The six color families are laid out across their respective sections of the color wheel.
The boxes on the scope represent broadcast-safe color levels on the interior with color-clipping levels on the outside.
The vector scope works by sampling the color info of each pixel in each frame. This data then gets evaluated and plotted on the vector scope based on two data points: the hue and saturation levels of the pixel. Hue is represented around the perimeter of the scope, while saturation is represented by the distance of the point from the center of the scope. Black and white footage pixels will be in the center of the scope.
Perhaps one of the most useful features of the vector scope is the skin tone line. This is represented differently depending on the vector scope being used. In Premiere it is the top left section of the graph line.
Regardless of skin color, this line always lies on proper skin tone because this specific portion of the graph is the color of blood running under the skin. Regardless of your grade, make sure that your skin tones fall on this line.
To check your skin tones, simply zoom the viewer in or mask around the largest part of the frame with skin. The vector scope will update and show you your isolated skin tone values. Adjust with hue controls first and then tweak the color temperature to dial it in.
With these four scopes, you are fully equipped to tackle any color grading or other image mastering projects that might come your way. If you aren’t actively using your scopes on every project, there’s never been a better time to start!
Cover image via Simon Mayer.
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