Back to Aurora Vision Studio website

You are here: Start » Filter Reference » Image » Image Local Transforms » GradientDirAndPresenceImage

GradientDirAndPresenceImage


Module: FoundationBasic

Computes an image of gradient directions mapped to the range from 1 to 255. Zero means "no edge".

Applications

For highly optimized analysis of gradient directions.
Name Type Range Description
Input value inImage Image Input image
Input value inRoi Region* Range of output pixels to be computed
Input value inOperator GradientMaskOperator Defines how the gradient is computed
Input value inEdgeThreshold Real 0.01 - Minimum edge magnitude (other pixels will be set to 0)
Input value inAngleRange AngleRange Range of output angles
Output value outDirectionsImage Image

Description

The operation computes the angle of the intensity change direction at each pixel of the inImage. Firstly the selected inOperator is used to obtain two-dimensional gradient vector at each pixel. When this vector length exceeds inEdgeThreshold the angle of the vector is calculated, scaled and stored in outDirectionsImage pixel.

This operation always generates a single-channel image with the uint8 pixel type on the output, regardless of the input image format, with following pixel values:

  • When gradient length does not exceed threshold, the value of 0 is stored in pixel.
  • When gradient length exceeds threshold, its angle is scaled to range 0..255 and stored in pixel value.

When a pixel value is non-zero, one can restore the original angle with the formula:

	double angle = value * 360.0 / 255.0;   // if inAngleRange == _0_360
	double angle = value * 180.0 / 255.0;   // if inAngleRange == _0_180
	double angle = value * 90.0 / 255.0;    // if inAngleRange == _0_90

To measure the angular distance between two directions described by two non-zero pixel values, use the following formulas:

    int valueDif = abs(inValue1 - inValue2);
	double angleDif = (valueDif < 128 ? (double)valueDif : (255.0 - valueDif)) * 360.0 / 255.0;  // if inAngleRange == _0_360
	double angleDif = ((double)valueDif) * 180.0 / 255.0;                                        // if inAngleRange == _0_180
	double angleDif = ((double)valueDif) * 90.0 / 255.0;                                         // if inAngleRange == _0_90

Hardware Acceleration

This operation is optimized for SSE41 technology for pixels of type: UINT8.

This operation is optimized for AVX2 technology for pixels of type: UINT8.

This operation is optimized for NEON technology for pixels of type: UINT8.

This operation supports automatic parallelization for multicore and multiprocessor systems.

Errors

This filter can throw an exception to report error. Read how to deal with errors in Error Handling.

List of possible exceptions:

Error type Description
DomainError Region exceeds an input image in GradientDirAndPresenceImage.

Complexity Level

This filter is available on Expert Complexity Level.

See Also

  • GradientImage – Computes a gradient image with smoothing operator of any size. The output pixels are signed.