An Abstract of Color
This abstract translates complex color theory into an explorable experience. For video engineers and enthusiasts, it demystifies everything from the physics of light to the technical standards that define modern video, helping you master the art and science of color.
Color Fundamentals
This section explores the bedrock principles of video color. We'll start with the physics of light and human perception, which explain *why* we see color the way we do. Then, we'll dive into colorimetry—the science of measuring color—and see how standards like the CIE 1931 Chromaticity Diagram provide a universal language for defining and comparing the range of colors (gamuts) that different video systems can reproduce.
CIE 1931 Chromaticity Diagram
The CIE 1931 diagram is a map of all colors visible to the average human. The outer horseshoe shape represents pure, monochromatic light. Video color spaces are shown as triangles, defining the gamut (range of colors) they can reproduce. Interact with the checkboxes to compare the gamuts of key video standards.
Human Perception & Color Models
Human color vision is based on three types of cone cells in our eyes, sensitive to short (Blue), medium (Green), and long (Red) wavelengths of light. This is the principle of trichromacy. Video displays leverage this by using an additive RGB color model, mixing red, green, and blue light to create a vast spectrum of colors.
However, for efficient video compression, the YCbCr model is used. It separates brightness (Luma, Y') from color information (Chroma, Cb/Cr). This is crucial because our eyes are more sensitive to detail in brightness than in color, allowing color information to be compressed with minimal visual impact.
Digital Representation
This section focuses on how the continuous world of color is translated into discrete digital data. We will examine bit depth, which determines the number of available colors and the smoothness of gradients, and chroma subsampling, a compression technique fundamental to modern video codecs. Understanding these concepts is essential for appreciating the trade-offs between image quality, file size, and processing requirements.
Color Depth (Bit Depth)
Bit depth defines the number of shades available for each color channel. Higher bit depth means more colors, resulting in smoother gradients and more flexibility for color grading. 8-bit is standard for SDR, but 10-bit or higher is essential for HDR and professional workflows to avoid "color banding."
~16.7 Million Colors
256 shades per channel
Chroma Subsampling
Chroma subsampling is a compression technique that reduces color data by sampling color at a lower resolution than brightness. This works because human vision is less sensitive to color detail than to luminance. The notation J:a:b (e.g., 4:2:2) describes this sampling. Select a scheme to see how it works.
In the Camera
Capturing a great image starts in the camera. This section covers the fundamental controls of exposure—the "exposure triangle" of aperture, shutter speed, and ISO—and how they impact not just brightness but also creative elements like depth of field and motion blur. We will also explore transfer functions (like Log curves), which are crucial for capturing the maximum possible dynamic range from the camera's sensor for post-production flexibility.
The Exposure Triangle
Exposure is controlled by three interdependent settings. Changing one requires adjusting others to maintain the desired brightness. Each setting also has a critical secondary effect on the image's final look.
Aperture (f-stop)
Controls the size of the lens opening. A wider aperture (e.g., f/1.8) lets in more light and creates a shallow depth of field (blurry background).
Shutter Speed
Controls how long the sensor is exposed to light for each frame. A slower speed (e.g., 1/50s) creates more motion blur, often considered cinematic.
ISO/Gain
Amplifies the sensor signal. Higher ISO allows shooting in darker conditions but introduces digital noise and reduces dynamic range.
Transfer Functions (OETF)
An OETF (Opto-Electronic Transfer Function) translates scene light into a video signal. While standard gamma curves (like Rec.709) are for direct viewing, Log curves are used to capture high dynamic range.
Log footage looks flat and desaturated, but it preserves highlight and shadow detail, providing maximum flexibility for color grading.
Post-Production & Display
This final section bridges the gap between capture and viewing. We'll explore color grading, the artistic process of manipulating color and tone to create a specific look. We will also cover High Dynamic Range (HDR), which represents a significant leap forward in display technology, enabling brighter highlights, deeper blacks, and a wider range of colors for a more realistic and immersive viewing experience.
Color Grading & LUTs
Color grading is the process of altering and enhancing the color of a video to set a mood, create a style, or correct issues. This is where "flat" Log footage is transformed into its final look.
Look-Up Tables (LUTs) are a key part of this process. A Technical LUT is used to convert footage from one color space to another (e.g., from camera Log to Rec.709). A Creative LUT applies a specific artistic look or color palette.
High Dynamic Range (HDR)
HDR is a technology that allows displays to show a much greater range of brightness and color than Standard Dynamic Range (SDR). Key HDR formats include:
- HDR10: An open standard using the PQ transfer function and static metadata. It's a common baseline for HDR content.
- Dolby Vision: A proprietary format that uses dynamic metadata, allowing for scene-by-scene or even frame-by-frame optimization of brightness and tone mapping.
- HLG (Hybrid Log-Gamma): A royalty-free standard primarily designed for broadcast. It's backward-compatible, meaning an HLG signal can be viewed on both SDR and HDR displays.
Video Standards Comparison
The world of video is governed by standards that define its color characteristics. Rec.709 has been the workhorse for HDTV, while DCI-P3 is used for cinema, and Rec.2020 is the future-facing standard for UHD and HDR, offering a vastly wider color gamut.
| Feature | Rec. 709 / sRGB | DCI-P3 (Theatrical) | Display P3 | Rec. 2020 |
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