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visionhdl.MeasureTiming

Measure timing of pixel control structure input

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Description

The visionhdl.MeasureTiming System object™ measures the timing parameters of a video stream. The Vision HDL Toolbox™ streaming pixel protocol implements the timing of a video system, including inactive intervals between frames. These inactive intervals are called blanking intervals. Many Vision HDL Toolbox objects require minimum blanking intervals. You can use the timing parameter measurements from this object to check that your video stream meets these requirements. If you manipulate the control signals of your video stream, you can use this object to verify the resulting control signals. To determine the parameters of each frame, the object measures time steps between the control signals in the input structure.

For details on the pixel control bus and the dimensions of a video frame, see Streaming Pixel Interface. For more information on blanking intervals, see Configure Blanking Intervals.

To measure the timing of the pixel control structure input:

  1. Create the visionhdl.MeasureTiming object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

MT = visionhdl.MeasureTiming

Description

example

MT = visionhdl.MeasureTiming returns a System object that measures the average frame timing of a video stream.

Usage

Syntax

[activePixels,activeLines,totalPixels,totalLines,horizBlank,vertBlank] = MT(ctrlin)

Description

example

[activePixels,activeLines,totalPixels,totalLines,horizBlank,vertBlank] = MT(ctrlin) incorporates the current pixel location into calculations of video frame timing. The control signals, ctrlin, associated with each pixel indicate the location of this pixel relative to the active frame boundaries. The input object measures the time steps between the control signals to determine the parameters of each frame.

For details about the pixel stream format, see Streaming Pixel Interface.

Input Arguments

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Control signals accompanying the input pixel stream, specified as a pixelcontrol structure containing five logical data type signals. The signals describe the validity of the pixel and its location in the frame. For more details, see Pixel Control Structure.

Data Types: struct

Output Arguments

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The diagram shows the output measurements, as determined from the pixel stream control signals.

Logic analyzer waveform that shows six time measurements between control signals

  • 1 — Active pixels per line

  • 2 — Active lines per frame (count hStart pulses)

  • 3 — Total pixels per line

  • 4 — Total lines per frame (cycles divided by total pixels per line)

  • 5 — Horizontal blanking

  • 6 — Vertical blanking (cycles, minus horizontal blanking, divided by total pixels per line)

For details on the pixel control bus and the dimensions of a video frame, see Streaming Pixel Interface.

Note

Measurements from the first simulated frame are incorrect because some parameters require measurements between frames. Before using the results, simulate at least two frames.

This value is measured between hStart and hEnd. See marker 1 in the diagram.

Data Types: double

This value is measured as the number of hStart pulses between vStart and vEnd. See marker 2 in the diagram.

Data Types: double

This value is measured from hStart to the next hStart, including the horizontal blanking interval. See marker 3 in the diagram.

Data Types: double

This value is measured by the interval from vEnd to the next vEnd, divided by totalPixels. It includes the vertical blanking interval. See marker 4 in the diagram.

Data Types: double

The horizontal blanking interval is the number of inactive pixels between lines of a frame. This value is measured between hEnd and the next hStart. See marker 5 in the diagram.

Data Types: double

The vertical blanking interval is the number of inactive lines between frames. This value is measured from vEnd to the next vStart, adjusted to remove horizBlank, then divided by totalPixels. See marker 6 in the diagram.

Data Types: double

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

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stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

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Open Live Script

This example shows how to use the MeasureTiming object to observe the frame parameters in a custom video stream. The example creates customized padding around an image frame and converts the frame to streaming video. It uses the MeasureTiming object to confirm that the streaming video parameters match the custom settings.

Use a FrameToPixels object to specify a small custom-size frame with customized blanking intervals. To obtain a frame of this size, select a small section of the input image.

frm2pix = visionhdl.FrameToPixels( ...
      'VideoFormat','custom', ...
      'ActivePixelsPerLine',32, ...
      'ActiveVideoLines',18, ...
      'TotalPixelsPerLine',42, ...
      'TotalVideoLines',26, ...
      'StartingActiveLine',6, ...     
      'FrontPorch',5);    
[actPixPerLine,actLine,numPixPerFrm] = getparamfromfrm2pix(frm2pix);  

frmFull = imread('rice.png');
frmIn = frmFull(74:73+actLine,104:103+actPixPerLine);
imshow(frmIn)

Create a MeasureTiming object to observe the parameters of the serial pixel output from the FrameToPixels object. 

measure = visionhdl.MeasureTiming;

Serialize the input frame.

[pixInVec,ctrlInVec] = frm2pix(frmIn);

Some parameters require measurements between frames, so you must simulate at least two frames before using the results. Because you serialized only one input frame, process that frame twice to measure all parameters correctly. 

for f = 1:2
      for p = 1:numPixPerFrm
          [activePixels,activeLines,totalPixels,totalLines, ...
              horizBlank,vertBlank] = measure(ctrlInVec(p));
      end
      fprintf('\nFrame %d:\n',f)
      fprintf('activePixels: %f\n',activePixels)
      fprintf('activeLines: %f\n',activeLines)
      fprintf('totalPixels: %f\n',totalPixels)
      fprintf('totalLines: %f\n',totalLines)
      fprintf('horizBlank: %f\n',horizBlank)
      fprintf('vertBlank: %f\n',vertBlank)
end
Frame 1:

activePixels: 32.000000

activeLines: 18.000000

totalPixels: 42.000000

totalLines: 22.880952

horizBlank: 10.000000

vertBlank: 4.880952

Frame 2:

activePixels: 32.000000

activeLines: 18.000000

totalPixels: 42.000000

totalLines: 26.000000

horizBlank: 10.000000

vertBlank: 8.000000

The measurements after the first frame are not accurate. However, after the second frame, the measurements match the parameters chosen in the FrameToPixels object.

Version History

Introduced in R2016b

See Also

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