Chroma Resampling

Downsample or upsample chrominance components of images

• 

Libraries:
Computer Vision Toolbox / Conversions

Description

The Chroma Resampling block resamples the chrominance components of an input image. Chroma resampling consists of these operations:

• Downsample — Reduces the bandwidth required for transmission or storage of a signal. You can prevent aliasing by applying a lowpass filter to bandlimit the input signal.

• Upsample — Expands the bandwidth of the signal. This block performs interpolation to approximate the missing chrominance values.

Examples

Perform Chroma Resampling of Image

Downsample and upsample the chrominance components of an image.

• Open Script

Ports

Input

Cb — Blue-difference chrominance component of image

matrix

Blue-difference chrominance component of the image, specified as an M-by-D matrix. D is half the width of the image.

Data Types: single | double | uint8

Cr — Red-difference chrominance component of image

matrix

Red-difference chrominance component of the image, specified as an M-by-D matrix. D is half the width of the image.

Data Types: single | double | uint8

Output

Cb — Blue-difference chrominance component of image

matrix

Blue-difference chrominance component of image, returned as an M-by-P matrix. P is half the width of the resampled image. If you downsample the input image, P is less than D. If you upsample the input image, P is greater than D.

Data Types: single | double | int8 | uint8

Cr — Red-difference chrominance component of image

matrix

Red-difference chrominance component of image, returned as an M-by-P matrix. P is half the width of the resampled image. If you downsample the input image, P is less than D. If you upsample the input image, P is greater than D

Data Types: single | double | int8 | uint8

Parameters

Resampling — Chrominance resampling method

4:4:4 to 4:2:2 (default) | 4:4:4 to 4:2:0 (MPEG1) | 4:4:4 to 4:2:0 (MPEG2) | ...

Specify the resampling method to use to downsample or upsample the chrominance components of the image.

These options specify downsampling operations:

• 4:4:4 to 4:2:2

• 4:4:4 to 4:2:0 (MPEG1)

• 4:4:4 to 4:2:0 (MPEG2)

• 4:4:4 to 4:1:1

• 4:2:2 to 4:2:0 (MPEG1)

• 4:2:2 to 4:2:0 (MPEG2)

These options specify upsampling operations:

• 4:2:2 to 4:4:4

• 4:2:0 (MPEG1) to 4:2:2

• 4:2:0 (MPEG1) to 4:4:4

• 4:2:0 (MPEG2) to 4:2:2

• 4:2:0 (MPEG2) to 4:4:4

• 4:1:1 to 4:4:4

For more information, see Chrominance Resampling Formats.

Antialiasing filter — Chroma downsampling antialiasing filter

Default (default) | User-defined | None

Specify the lowpass filter that the block uses to prevent aliasing.

• Default — The block uses a built-in lowpass filter.

• User-defined — Specify custom filter coefficients for the block. Depending on the value of the Resampling parameter, this option enables the Horizontal filter coefficients parameter, the Vertical filter coefficients parameter, or both.

• None — The block does not filter the input signal.

Dependencies

To enable this parameter, set the Resampling parameter to one of these options:

• 4:4:4 to 4:2:2

• 4:4:4 to 4:2:0 (MPEG1)

• 4:4:4 to 4:2:0 (MPEG2)

• 4:4:4 to 4:1:1

• 4:2:2 to 4:2:0 (MPEG1)

• 4:2:2 to 4:2:0 (MPEG2)

.

Horizontal filter coefficients — Coefficients for horizontal lowpass filter

[0.2 0.6 0.2] (default) | row vector

Specify the horizontal filter coefficients as a vector of even number of elements to apply to your input signal.

Dependencies

To enable this parameter, you must:

• Set the Resampling parameter to one of these options:

  • 4:4:4 to 4:2:2

  • 4:4:4 to 4:2:0 (MPEG1)

  • 4:4:4 to 4:2:0 (MPEG2)

  • 4:4:4 to 4:1:1

• Set the Antialiasing filter parameter to User-defined.

Vertical filter coefficients — Coefficients for vertical lowpass filter

[0.5 0.5] (default) | row vector

Specify the filter coefficients as a vector of odd number of elements to apply to your input signal.

Dependencies

To enable this parameter, you must:

• Set the Resampling parameter to one of these options:

  • 4:4:4 to 4:2:0 (MPEG1)

  • 4:4:4 to 4:2:0 (MPEG2)

  • 4:2:2 to 4:2:0 (MPEG1)

  • 4:2:2 to 4:2:0 (MPEG2)

• Set the Antialiasing filter parameter to User-defined.

Interpolation — Chrominance upsampling interpolation method

linear (default) | pixel replication

Specify whether the block uses linear interpolation or pixel replication interpolation to approximate the missing chrominance values when upsampling an image.

• linear — The block uses linear interpolation to calculate the missing values.

• pixel replication — The block replicates the chrominance values of the neighboring pixels to assign values to the additional pixels in the upsampled image.

Dependencies

To enable this parameter, set the Resampling parameter to one of these options:

• 4:2:2 to 4:4:4

• 4:2:0 (MPEG1) to 4:2:2

• 4:2:0 (MPEG1) to 4:4:4

• 4:2:0 (MPEG2) to 4:2:2

• 4:2:0 (MPEG2) to 4:4:4

• 4:1:1 to 4:4:4

.

Input image is transposed (data order is row major) — Read data row-wise

off (default) | on

Enable this parameter to read data elements row-wise.

Block Characteristics

Data Types	double | integer | single
Multidimensional Signals	no
Variable-Size Signals	yes

Algorithms

Chrominance Resampling Formats

Chrominance resampling format is represented as a three-part ratio J:a:b (for example, 4:2:2). The three-parts are represented as:

• J — Horizontal sampling reference

• a — Number of chrominance samples (Cr, Cb) in the first row of J pixels.

• b — Number of chrominance samples (Cr, Cb) in the second row of J pixels

The Chroma Resampling block supports these formats:

• Chrominance resampling format 4:4:4

  

• Chrominance resampling format 4:2:2

  

• Chrominance resampling format 4:1:1

  

• Chrominance resampling format 4:2:0 (MPEG1)

  

• Chrominance resampling format 4:2:0 (MPEG2)

  

References

[1] Haskell, Barry G., Atul Puri, and Arun N. Netravali. Digital Video: An Introduction to MPEG-2. Digital Multimedia Standards Series. New York: Chapman & Hall : International Thomson Pub, 1997.

[2] Wang, Yao, Jörn Ostermann, and Ya-Qin Zhang. Video Processing and Communications. Prentice-Hall Signal Processing Series. Upper Saddle River, N.J: Prentice Hall, 2002.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a