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Can’t Understand the Oscilloscope?
Yesterday we embarked on a color grading journey, but relying solely on the human eye on potentially inaccurate displays is like driving in a fog. Today, we will equip ourselves with a “radar” and “GPS”—that is the oscilloscope. Don’t be intimidated by these graphs; they are your most loyal and objective partners, revealing the truth about brightness and color.
Core Concepts: The waveform monitor shows brightness exposure, the vector scope shows color balance and saturation, and the histogram shows pixel distribution. They are objective and reliable color grading dashboards that can free you from the misleading displays.
01
Introduction: Why Do We Need an Oscilloscope?
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Your monitor may be color-imbalanced, and ambient light can affect your judgment. But the oscilloscope does not lie; it visually displays the exposure and color information of the image using scientific data. Learning to read the oscilloscope is a necessary step towards professional color grading.
02
Waveform Monitor: Your “Exposure Meter”
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The waveform monitor is the most commonly used and important oscilloscope; it displays the brightness value of every pixel in the image.
Y-axis (Vertical): Brightness.
Top (100% IRE): Pure white. Absolute no-go! If the waveform peaks at the top, it means overexposure, and details are permanently lost.
Middle area: Midtones. Most detail and color information are here.
Bottom (0% IRE): Pure black. If the waveform sinks to the bottom, it means dead black, and details cannot be recovered.
X-axis (Horizontal): Corresponds to the image from left to right.
How to use it to judge exposure?
Goal: Let the waveform distribute across the entire range but not touch the top and bottom.
Underexposure: The waveform is overall squeezed at the bottom.
Solution: Increase gain or offset.
Overexposure: The waveform is overall squeezed at the top, even getting “clipped.”
Solution: Decrease gain or highlights.
Insufficient contrast (image appears gray): The waveform is concentrated in the middle, with both ends empty.
Solution: Increase contrast, pushing the white point up and pulling the black point down.
03
Vector Scope: Your “Color Radar”
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The vector scope is specifically used to analyze the hue and saturation of the image.
Center point: Black/Neutral Gray. The farther from the center, the higher the saturation.
Six color targets: Corresponding to R (Red), G (Green), B (Blue), Y (Yellow), C (Cyan), M (Magenta). The points on the waveform leaning towards which color target indicate the color bias of the image.
How to use it to judge color?
Goal: Achieve balanced and natural colors.
White balance correction:
Find an area in the image that should be white or gray.
Use the eyedropper tool to click on it.
Observe the vector scope; if the waveform overall contracts towards the center point, it indicates that the white balance has been corrected.
Skin tone check: Healthy skin tones of Caucasians, Asians, and Africans will fall on a diagonal line known as the “Skin Tone Indicator Line” (from the center pointing towards the lower left area, between red and yellow). If your actor’s skin tone deviates from this line, adjustments may be needed.
04
Histogram: Your “Pixel Distribution Map”
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You may have seen it in your camera; its function is similar to the waveform monitor but displays differently.
X-axis (Horizontal): Brightness. From left (black) to right (white).
Y-axis (Vertical): The number of pixels at that brightness level.
How to use it to judge exposure?
Goal: The graph should be evenly distributed, not sticking to the left or right wall.
Underexposure: The graph is overall leaning towards the left side.
Overexposure: The graph is overall leaning towards the right side.
High-key image (bright): The graph leans towards the right side, but the far right does not touch the edge.
Low-key image (dark): The graph leans towards the left side, but the far left does not touch the edge.
05
Step-by-Step Practice: Using the Oscilloscope for Primary Color Grading
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Let’s use a standard process to correct a dim and blue-tinted lens.
Open all oscilloscopes and display them next to your monitor.
Correct exposure (look at the waveform monitor/histogram):
Observe the waveform monitor and find it overall low.
In the software, increase gain or offset until the waveform rises to the middle area, with the brightest part close to but not touching the 100% IRE line.
Correct white balance (look at the vector scope):
Observe the vector scope and find the waveform overall leaning towards the blue (B) color target.
In the software, use the color temperature/tint controls to reduce blue (equivalent to increasing yellow) until the vector scope’s graph overall contracts towards the center.
Final check:
Recheck all oscilloscopes to ensure correct exposure and color balance.
