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Video Input

Get video data from system video devices

  • Library:
  • Simulink Desktop Real-Time

  • Video Input block

Description

The Video Input block lets you get video data from system video devices. The camera device support includes support for video input from standard USB video class devices (webcams). The block also can output video frames status as ready or corrupted, and include the frame presentation timestamp. You can select the output format and region-of-interest (ROI).

The block gets the camera resolution from the configuration of the data acquisition board, for example a system camera that you install by using the block option to Install new board > Standard Devices > Camera.

The device configuration interface for the camera consists of camera ID, frame dimensions (width and height), and optional luminance channel toggle.

  • The camera ID is an integer number greater than or equal to one, specifying order of the accessed camera in the system. For example, the first, primary camera listed by the system has ID of 1. The camera ID default value is 1.

  • The frame width and height determine the required resolution of the video input. Maximum allowed resolution is FHD (1920x1080). The default dimensions are VGA (640x480).

  • The luminance channel toggle is a checkbox determining if the camera device should calculate luminance channel of the video, in addition to the RGB channels. Its default value is TRUE (checked).

You can test or accept the configuration by using Test and OK buttons. In case the camera configuration is invalid, the test or setting process fails and shows an error message. The camera configuration can fail for multiple reasons, for example absence of a camera with specified ID in the system, the specified resolution not being supported by the camera, or hardware failure.

Ports

Input

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If you configure the ROI origin source as External, the ROI Input Data port is available on the block. The data input is a vector of ROI origin coordinates. Its elements correspond to X (horizontal) and Y (vertical) coordinates of the top-left corner of the ROI area. If the ROI origin source is Internal, the ROI origin coordinates are set by the ROI origin parameter.

Output

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The Data output provides the video data output. The dimensions and format of the port depend on the configuration of ROI parameters and output format.

If the output format is set to RGB, the video data output is an height x width x 3 matrix of uint8 values. The height and width are height and width of the ROI area. A value of the output matrix on coordinates [y,x,c] corresponds to a value of the image on the coordinates [y,x] of the color channel c.

If the output format is set to Luminance, the video data output is an height x width matrix of UINT8 values. The height and width are height and width of the ROI area. A value of the output matrix on coordinates [y,x] correspond to the luminance of the pixel on coordinates [y,x].

The Frame Ready output is a Boolean output, which value is True (1), if, and only if, the new frame from the camera is ready. If you enable the Show "Frame Ready" port parameter, the Frame Ready port is available on the block.

Data Types: Boolean

The Frame Error output is a Boolean output. The value is True (1) if an error has occurred during frame acquisition, and the value is False (0) if no error occurred. Error conditions include:

  • When the acquired frame might be corrupted

  • When the ROI area exceeds the frame boundary

If you enable the Show "Frame Error" port parameter, the Frame Error port is available on the block.

Data Types: Boolean

The Timestamp output in seconds is a Double output, which value corresponds to the presentation timestamp of the frame on the video data output. The frame timestamp is relative to the simulation start. If you enable the Show frame timestamp port parameter, the Timestamp port is available on the block.

Data Types: double

In Connected IO mode, returns the number of timer ticks that your model lags behind the real-time kernel. When the model lags by more than Maximum missed ticks, the software reports an error and simulation stops.

Dependency

When you select Show “Missed Ticks” port, this port is visible.

Data Types: double

Parameters

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Enter a value, in seconds, that represents how frequently you want the block to execute and interact with the I/O hardware. The block synchronizes your model with the real-time clock at this sample rate.

If you are using a fixed-step solver, enter the value that you entered as the Fixed step size configuration parameter or an integer multiple of that value.

Programmatic Use

Block Parameter: SampleTime

In Connected IO mode, enter the number of timer ticks that your model can lag behind the real-time kernel. When the model lags behind by this number or fewer timer ticks, the software assumes that the lag is temporary. It allows the model to catch up, even if the model misses some ticks. When the model lags by more than this number, the software reports an error and simulation stops.

In Run in Kernel mode, the software ignores this value.

Programmatic Use

Block Parameter: MaxMissedTicks

In Connected IO mode, select this check box to send the number of missed ticks to output port Missed Ticks.

In Run in Kernel mode, the Missed Ticks port is zero.

Programmatic Use

Block Parameter: ShowMissedTicks

In Connected IO mode, select this check box to grant other programs more CPU time while the kernel waits for a response from the hardware.

In Run in Kernel mode, the software ignores this value.

Programmatic Use

Block Parameter: YieldWhenWaiting

Select whether the ROI area origin, the pixel coordinates of its top-left corner, values are controlled by an external source..

  • When Internal is selected, the origin is controlled by the block parameters.

  • When External is selected, the origin is controlled by the block input port.

Programmatic Use

Block Parameter: ROIOriginSource

The ROI origin specifies coordinates of the top-left corner of ROI area; X for horizontal and Y for vertical. If ROI origin source is configured as Internal, the ROI origin 2-element vector values to specify the top-left-corner origin point can be selected in the block parameters dialog box.

Programmatic Use

Block Parameter: RoiOrigin

The ROI Dimensions specify the dimensions of the width-height of the ROI area for the configured device; W for width and H for height.

Programmatic Use

Block Parameter: RoiDimensions

The Frame format determines whether the video data are served in RGB format or are served in luminance format. Changing the output format changes the dimensions of the output video data signal; HxWx3 for RGB and HxW for Luminance.

Programmatic Use

Block Parameter:Channels

When set to on, the block includes a Frame Ready output port.

Programmatic Use

Block Parameter: ShowReady

When set to on, the block includes a Frame Error output port.

Programmatic Use

Block Parameter: ShowError

When set to on, the block includes a Timestamp output port.

Programmatic Use

Block Parameter: ShowTimestamp

Version History

Introduced in R2022a