Frame To Pixels

Convert frame-based video to pixel stream

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Libraries:
Vision HDL Toolbox / I/O Interfaces

Description

The Frame To Pixels block converts color or grayscale video frames to a pixel stream and control signals. The control signals indicate the validity of each pixel and its location in the frame. The pixel stream format can include padding pixels around the active frame. You can configure the frame and padding dimensions by selecting a common video format or by specifying custom dimensions. The pixel stream can support single pixel streaming or multipixel streaming. Multipixel streaming provides 2, 4, or 8 pixels per clock cycle to support high-rate or high-resolution formats. For details of the pixel stream format, see Streaming Pixel Interface.

This block itself does not support HDL code generation. However, you can use this block to generate input for a separate subsystem targeted for HDL code generation.

If your model converts frames to a pixel stream and later converts the stream back to frames, specify the same video format for the Frame To Pixels block and the Pixels To Frame block.

Examples

Gamma Correction

Model pixel-streaming gamma correction for hardware designs. The model compares the results from the Vision HDL Toolbox™ Gamma Corrector block with the results generated by the full-frame Gamma block from Computer Vision Toolbox™.

• Open Model

Filter Multipixel Video Streams

Design filters that operate on a multipixel input video stream. Use multipixel streaming to process high-resolution or high-frame-rate video with the same synthesized clock frequency as a single-pixel streaming interface. Multipixel streaming also improves simulation speed and throughput because fewer iterations are required to process each frame, while maintaining the hardware benefits of a streaming interface.

• Open Model

Ports

Input

frame — Full image frame

array

Full image frame, specified as an Active pixels per line-by-Active video lines-by-N array. The first two array dimensions are the height and width of the active image specified by the Video format parameter. N is the Number of components used to express a single pixel. Number of components can be one, three, or four.

Data Types: single | double | int | uint | Boolean | fixed point

Output

pixel — Image pixel or pixels

scalar | vector

For single pixel streams, pixel is a single image pixel returned as a scalar or a vector of 1-by-Number of components values. For multipixel streams, pixel is a matrix of Number of pixels-by-Number of components pixel intensity values.

The output data type is the same as the data type of the frame port.

ctrl — Control signals associated with pixel stream

pixelcontrol bus

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

For multipixel streaming, each vector of pixel values has one set of control signals. Because the vector has only one valid signal, the pixels in the vector must be either all valid or all invalid. The hStart and vStart signals apply to the pixel with the lowest index in the vector. The hEnd and vEnd signals apply to the pixel with the highest index in the vector.

Data Types: bus

Parameters

Number of components — Number of values used to represent each pixel

1 (default) | 3 | 4

Number of values used to represent each pixel. Each pixel can have 1, 3, or 4 components.

• For grayscale video, set this parameter to 1.

• For color video, for example, {R,G,B} or {Y,Cb,Cr}, set this parameter to 3.

• For color video with an alpha channel for transparency, set this parameter to 4.

To process multicomponent streams for blocks that do not support multicomponent input, replicate the block for each component. The pixelcontrol bus for all components is identical, so you can connect the ctrl output of the Frame To Pixels block to each replicated block.

Number of pixels — Number of pixels streamed per time step

1 (default) | 2 | 4 | 8

Number of pixels transferred on the streaming interface for each time step, specified as 1, 2, 4, or 8. To enable multipixel streaming and increase throughput for high-resolution or high-frame-rate video, set this parameter to 2, 4 or 8. Multipixel streaming processes more pixels with the same clock frequency as a single-pixel streaming interface.

Video Resolution	Clock Frequency Required for Single-Pixel Streaming at 60 fps	Clock Frequency Required for Multipixel Streaming at 60 fps (4 pixels)
1080p	150 MHz	37.5 MHz
4k UHD	600 MHz	150 MHz
8k UHD	1200 MHz	300 MHz

Video format — Dimensions of active and inactive regions in video frame

1080p (default) | 240p | 480p | 480pH | 576p | 720p | 768p | 1024p | 1200p | 2KCinema | 4KUHDTV | 8KUHDTV | Custom

Dimensions of active and inactive regions in a video frame. To select a predefined format, select from the Video format list. The actual frame dimensions are displayed in the Video Format Parameters section. For a custom format, select Custom, and then specify the dimensions as integers.

The dimensions are defined in the diagram.

Note

The sample time of your video source must match the total number of pixels in the frame of your Frame To Pixels block. The total number of pixels is Total pixels per line × Total video lines, so set the sample time to this value.

If your frame size is large, you may reach the fixed-step solver step size limit for sample times in Simulink^®, and receive an error like this.

The computed fixed step size (1.0) is 1000000.0 times smaller than all
the discrete sample times in the model. 

You can avoid this error by choosing the variable-step solver.

Video Format	Active Pixels Per Line	Active Video Lines	Total Pixels Per Line	Total Video Lines	Starting Active Line	Ending Active Line	Front Porch	Back Porch
240p	320	240	402	324	1	240	44	38
480p	640	480	800	525	36	515	16	144
480pH	720	480	858	525	33	512	16	122
576p	720	576	864	625	47	622	12	132
720p	1280	720	1650	750	25	744	110	260
768p	1024	768	1344	806	10	777	24	296
1024p	1280	1024	1688	1066	42	1065	48	360
1080p (default)	1920	1080	2200	1125	42	1121	88	192
1200p	1600	1200	2160	1250	50	1249	64	496
2KCinema	2048	1080	2750	1125	42	1121	639	63
4KUHDTV	3840	2160	4400	2250	42	2201	88	472
8KUHDTV	7680	4320	8800	4500	42	4361	88	1032
Custom	User- defined	User- defined	User- defined	User- defined	User- defined	User- defined	User- defined	User- defined

When using a custom format, the values you enter for the active and inactive dimensions of the image must add up to the total frame dimensions. If you specify a format that does not conform to these rules, the block reports an error.

• For the horizontal direction, Total pixels per line must be greater than or equal to Front porch + Active pixels per line. The block calculates Back porch = Total pixels per line − Front porch − Active pixels per line.

• For the vertical direction, Total video lines must be greater than or equal to Starting active line + Active video lines − 1. The block calculates Ending active line = Starting active line + Active video lines − 1.

When using the Line Buffer block, or blocks that use an internal line buffer, with a custom video format, further requirements apply:

• The horizontal blanking interval, or Back porch + Front porch, must meet these guidelines:

  • The total of Back porch + Front porch must be at least 2 times the largest kernel size of the algorithm in the blocks following the Frame To Pixel block.

  • If the kernel size is less than 4, and you are using edge padding, the total porch must be at least 8 pixels.

  • If you disable padding, the total porch must be at least 12 pixels.

  • The Back porch must be at least 6 pixels. This parameter is the number of inactive pixels before the first valid pixel in a frame.

  For more information on blanking intervals, see Configure Blanking Intervals.

When using multipixel streaming (Number of pixels > 1), these requirements apply.

• The video format must have horizontal dimensions divisible by the Number of pixels parameter value. The horizontal dimensions are set by these parameters: Active pixels per line, Total pixels per line, Front porch, and Back porch. Standard video protocols 480p, 768p, 1024p, 1080p, 1200p, 4k UHD, and 8k UHD support Number of pixels equal to 4 or 8.

• The minimum input frame size for multipixel streaming is 18 rows by 32 columns.

• Choose your kernel size and Active pixels per line such that (Active pixels per line)/(Number of pixels) is at least the kernel width.

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.

Version History

Introduced in R2015a

R2022a: Two pixels-per-clock streaming

The block can now generate multipixel streams that have 2 pixels per clock cycle.

R2020a: Multipixel-multicomponent streaming

The block can now generate multipixel-multicomponent streams. The MultiPixel-MultiComponent Video Streaming example shows how to use a multipixel and multicomponent pixel stream to process a high-resolution color image.

R2019b: Multipixel streaming

The block can now generate multipixel streams. You can set the Number of pixels parameter to 4 or 8. With this setting, the output of the block is a vector of 4 or 8 pixel values on each time step. For an example of how to use this feature, see Filter Multipixel Video Streams.

Video formats for multipixel streams must have horizontal dimensions divisible by the Number of pixels parameter value. These horizontal dimensions are set by the following parameters: Active pixels per line, Total pixels per line, Front porch, and Back porch. Standard video protocols 480p, 720p, 1080p, and 4k UHD support either 4 or 8 pixels at a time.