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Frame To Pixels

Convert frame-based video to pixel stream

  • Frame To Pixels block

Vision HDL Toolbox / I/O Interfaces


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.



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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


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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.

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


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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 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 ResolutionClock Frequency Required for Single-Pixel Streaming at 60 fpsClock Frequency Required for Multipixel Streaming at 60 fps (4 pixels)
1080p150 MHz37.5 MHz
4k UHD600 MHz150 MHz
8k UHD1200 MHz300 MHz

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.


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 FormatActive Pixels Per LineActive Video LinesTotal Pixels Per LineTotal Video LinesStarting Active LineEnding Active LineFront PorchBack Porch
240p320240 40232412404438
480p6404808005253651516 144
1080p (default)192010802200112542112188192

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 lineFront porchActive 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

Version History

Introduced in R2015a

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