Chroma subsampling

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Chroma subsampling is a technique used in video compression to reduce the amount of data required to represent color information in an image or video. This is achieved by taking advantage of the human visual system's lower sensitivity to color detail compared to luminance detail. Chroma subsampling works by encoding the color information at a lower resolution than the brightness information.

Overview

In digital images and videos, color is typically represented using the Y'CbCr color space, where:

• Y represents the luminance (brightness) component.
• Cb and Cr represent the chrominance (color) components.

Chroma subsampling reduces the resolution of the Cb and Cr components while keeping the Y component at full resolution. This reduction in color resolution can significantly decrease the amount of data needed to store or transmit the image or video, with minimal perceptible loss in quality.

Common Chroma Subsampling Ratios

Chroma subsampling ratios are usually expressed in the form J:a:b, where:

• J is the width of the sample region (typically 4).
• a is the number of chrominance samples in the first row of J pixels.
• b is the number of chrominance samples in the second row of J pixels.

Some common chroma subsampling ratios include:

• 4:4:4 - No subsampling, full resolution for all components.
• 4:2:2 - Horizontal subsampling by a factor of 2.
• 4:2:0 - Horizontal and vertical subsampling by a factor of 2.
• 4:1:1 - Horizontal subsampling by a factor of 4.

Applications

Chroma subsampling is widely used in various applications, including:

• Digital video compression formats such as MPEG, H.264, and HEVC.
• Broadcast television standards like NTSC, PAL, and SECAM.
• DVD and Blu-ray video formats.
• Streaming media services.

Advantages and Disadvantages

Advantages

• Reduces the amount of data required for storage and transmission.
• Maintains high visual quality by preserving luminance detail.

Disadvantages

• Can introduce artifacts, especially in images with high color detail.
• May result in color bleeding or blurring in certain scenarios.

See Also

• Color space
• Video compression
• Luminance
• Chrominance
• Y'CbCr color space
• MPEG
• H.264
• HEVC
• NTSC
• PAL
• SECAM
• DVD
• Blu-ray
• Streaming media