Color Space Converter

Convert color information between color spaces

Library:
Vision HDL Toolbox / Conversions

Description

The Color Space Converter block converts between R'G'B' and Y'CbCr color spaces, and also converts R'G'B' to intensity.

Note

The Color Space Converter block operates on gamma-corrected color spaces. However, for simplicity, the block and mask labels do not include the prime notation.

Ports

This block uses a streaming pixel interface with a pixelcontrol bus for frame control signals. This interface enables the block to operate independently of image size and format. All Vision HDL Toolbox™ blocks use the same streaming interface. The block accepts and returns a scalar pixel value and a bus that contains five control signals. The control signals indicate the validity of each pixel and its location in the frame. To convert a frame (pixel matrix) into a serial pixel stream and control signals, use the Frame To Pixels block. For a full description of the interface, see Streaming Pixel Interface.

Input

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`pixel` — Single image pixel
vector of three values

Single image pixel in Y'CbCr or R'G'B' color space, specified as a vector of three values. The values can be uint8, uint16, or fixdt(0,N,0), where N is from 8 through 16.

double and single data types are supported for simulation, but not for HDL code generation.

Data Types: single | double | uint8 | uint16 | fixed point

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Specify a pixelcontrol bus that contains five signals. The signals describe the validity of the pixel and its location in the frame. For more information, see Pixel Control Bus.

Data Types: bus

Output

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`pixel` — Single image pixel in new colorspace
scalar | vector of three values

Single image pixel in intensity, Y'CbCr, or R'G'B' color space, returned as a scalar or a vector of three values. The data type of the output pixels is the same as the data type of the input pixels.

double and single data types are supported for simulation, but not for HDL code generation.

Data Types: single | double | uint8 | uint16 | fixed point

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Control signals associated with the pixel stream, returned as a pixelcontrol bus that contains five signals. The signals describe the validity of the pixel and its location in the frame. For more information, see Pixel Control Bus.

Data Types: bus

Parameters

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`Conversion` — Type of color space conversion
`RGB to YCbCr` (default) | `YCbCr to RGB` | `RGB to intensity`

The block accepts input as a vector of three values representing a single pixel. If you choose RGB to intensity, the output is a scalar value. Otherwise, the output is a vector of three values.

`Use conversion specified by` — Conversion equation
`Rec. 601 (SDTV)` (default) | `Rec. 709 (HDTV)`

Conversion equation used between R'G'B' and Y'CbCr color spaces.

Dependencies

This parameter applies only when you set Conversion to RGB to YCbCr or YCbCr to RGB.

`Scanning standard` — HDTV scanning standard
`1250/50/2:1` (default) | `1125/60/2:1`

Scanning standard used to convert between R'G'B' and Y'CbCr color spaces in HDTV format.

Dependencies

This parameter applies when you set Use conversion specified by to Rec. 709 (HDTV).

Model Examples

Convert RGB Image to YCbCr 4:2:2 Color Space

Convert a pixel stream from R'G'B' color space to Y'CbCr 4:2:2 color space.

Algorithms

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Conversion Between R'G'B' and Y'CbCr Color Spaces

The following equations define R'G'B' to Y'CbCr conversion and Y'CbCr to R'G'B' conversion:

$[\begin{matrix} Y^{'} \\ C b \\ C r \end{matrix}] = [\begin{matrix} 16 \\ 128 \\ 128 \end{matrix}] + Α \times [\begin{matrix} R^{'} \\ G^{'} \\ B^{'} \end{matrix}]$

$[\begin{matrix} R^{'} \\ G^{'} \\ B^{'} \end{matrix}] = Β \times ([\begin{matrix} Y^{'} \\ C b \\ C r \end{matrix}] - [\begin{matrix} 16 \\ 128 \\ 128 \end{matrix}])$

The values in matrices A and B are based on your choices for the Use conversion specified by and Scanning standard parameters.

Matrix	Use conversion specified by = Rec. 601 (SDTV)	Use conversion specified by = Rec. 709 (HDTV)
Matrix	Use conversion specified by = Rec. 601 (SDTV)	Scanning standard = 1125/60/2:1	Scanning standard = 1250/50/2:1
A	$[\begin{matrix} 0.25678824 & 0.50412941 & 0.09790588 \\ - 0.1482229 & - 0.29099279 & 0.43921569 \\ 0.43921569 & - 0.36778831 & - 0.07142737 \end{matrix}]$	$[\begin{array}{l} 0 .18258588 0 .61423059 0 .06200706 \\ -0 .10064373 -0 .33857195 0 .43921569 \\ 0 .43921569 -0 .39894216 -0 .04027352 \end{array}]$	$[\begin{matrix} 0.25678824 & 0.50412941 & 0.09790588 \\ - 0.1482229 & - 0.29099279 & 0.43921569 \\ 0.43921569 & - 0.36778831 & - 0.07142737 \end{matrix}]$
B	$[\begin{matrix} 1.1643836 & 0 & 1.5960268 \\ 1.1643836 & - 0.39176229 & - 0.81296765 \\ 1.1643836 & 2.0172321 & 0 \end{matrix}]$	$[\begin{matrix} 1 .16438356 & 0 & 1 .79274107 \\ 1 .16438356 & -0 .21324861 & -0 .53290933 \\ 1 .16438356 & 2 .11240179 & 0 \end{matrix}]$	$[\begin{matrix} 1.1643836 & 0 & 1.5960268 \\ 1.1643836 & - 0.39176229 & - 0.81296765 \\ 1.1643836 & 2.0172321 & 0 \end{matrix}]$

Conversion from R'G'B' to Intensity

The following equation defines conversion from the R'G'B' color space to intensity:

$intensity = [\begin{matrix} 0.299 & 0.587 & 0.114 \end{matrix}] [\begin{matrix} R^{'} \\ G^{'} \\ B^{'} \end{matrix}]$

Data Types

For fixed-point and integer input, the block converts matrix A to fixdt(1,17,16), and matrix B to fixdt(1,17,14).

For double or single input, the block applies the conversion matrices in double type, and scales the Y'CbCr offset vector ([16,128,128]) by 1/255. The block saturates double or single R'G'B' and intensity outputs to the range [0,1].

The Y'CbCr standard includes headroom and footroom. For 8-bit data, luminance values in the range 16–235 and chrominance values in the range 16–240 are valid. The Color Space Converter block pins out-of-range input to these limits before calculating the conversion. The block scales the offset vector and the allowed headroom and footroom depending on the word length of the input signals. For example, when you convert a Y'CbCr input of type fixdt(0,10,0) to R'G'B', the block multiplies the offset vector by 2^{(10 –
8)} = 4. As a result, the valid luminance range becomes 64–940 and the valid chrominance range becomes 64–960.

Latency

Blocks with R'G'B' input have a latency of 9 cycles and blocks with Y'CbCr input have a latency of 10 cycles. The extra cycle is required to check for and correct headroom and footroom violations.

Note

When you use edge padding, use a horizontal blanking interval greater than twice the kernel width. This interval lets the block finish processing one line before it starts processing the next one, including adding padding pixels before and after the active pixels in the line. Standard streaming video formats use a horizontal blanking interval of about 25% of the frame width. This interval is much larger than the filters applied to each frame. When you disable edge padding, the horizontal blanking interval must be at least 12 cycles and is independent of the kernel size. If you are using a custom video format, set the horizontal blanking interval by using the Frame To Pixels block parameters. The horizontal blanking interval is equal to Total pixels per line – Active pixels per line or, equivalently, Front porch + Back porch. For more information, see Configure Blanking Intervals.

Extended Capabilities

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

This block supports C/C++ code generation for Simulink^® accelerator and rapid accelerator modes and for DPI component generation.

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

HDL Architecture

This block has a single, default HDL architecture.

HDL Block Properties

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays within your design. Distributed pipelining does not redistribute these registers. The default is `0`. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is `0`. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is `0`. For more details, see OutputPipeline (HDL Coder).

Documentation

Color Space Converter

Description

Ports

Input

`pixel` — Single image pixel
vector of three values

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Output

`pixel` — Single image pixel in new colorspace
scalar | vector of three values

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Parameters

`Conversion` — Type of color space conversion
`RGB to YCbCr` (default) | `YCbCr to RGB` | `RGB to intensity`

`Use conversion specified by` — Conversion equation
`Rec. 601 (SDTV)` (default) | `Rec. 709 (HDTV)`

Dependencies

`Scanning standard` — HDTV scanning standard
`1250/50/2:1` (default) | `1125/60/2:1`

Dependencies

Model Examples

Convert RGB Image to YCbCr 4:2:2 Color Space

Algorithms

Conversion Between R'G'B' and Y'CbCr Color Spaces

Conversion from R'G'B' to Intensity

Data Types

Latency

Extended Capabilities

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

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

See Also

Vision HDL Toolbox Documentation

Support

Documentation

Color Space Converter

Description

Ports

Input

pixel — Single image pixel vector of three values

ctrl — Control signals associated with pixel stream pixelcontrol bus

Output

pixel — Single image pixel in new colorspace scalar | vector of three values

ctrl — Control signals associated with pixel stream pixelcontrol bus

Parameters

Conversion — Type of color space conversion RGB to YCbCr (default) | YCbCr to RGB | RGB to intensity

Use conversion specified by — Conversion equation Rec. 601 (SDTV) (default) | Rec. 709 (HDTV)

Dependencies

Scanning standard — HDTV scanning standard 1250/50/2:1 (default) | 1125/60/2:1

Dependencies

Model Examples

Convert RGB Image to YCbCr 4:2:2 Color Space

Algorithms

Conversion Between R'G'B' and Y'CbCr Color Spaces

Conversion from R'G'B' to Intensity

Data Types

Latency

Extended Capabilities

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

HDL Code Generation Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

See Also

Vision HDL Toolbox Documentation

Support

`pixel` — Single image pixel
vector of three values

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

`pixel` — Single image pixel in new colorspace
scalar | vector of three values

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

`Conversion` — Type of color space conversion
`RGB to YCbCr` (default) | `YCbCr to RGB` | `RGB to intensity`

`Use conversion specified by` — Conversion equation
`Rec. 601 (SDTV)` (default) | `Rec. 709 (HDTV)`

`Scanning standard` — HDTV scanning standard
`1250/50/2:1` (default) | `1125/60/2:1`

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

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.