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GradientDirAndPresenceImage
Computes an image of gradient directions mapped to the range from 1 to 255. Zero means "no edge".
Syntax
void avl::GradientDirAndPresenceImage ( const avl::Image& inImage, atl::Optional<const avl::Region&> inRoi, avl::GradientMaskOperator::Type inOperator, float inEdgeThreshold, avl::Image& outDirectionsImage )
Parameters
Name | Type | Range | Default | Description | |
---|---|---|---|---|---|
inImage | const Image& | Input image | |||
inRoi | Optional<const Region&> | NIL | Range of output pixels to be computed | ||
inOperator | GradientMaskOperator::Type | Defines how the gradient is computed | |||
inEdgeThreshold | float | 0.01 - | 10.0f | Minimum edge magnitude (other pixels will be set to 0) | |
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;
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;
Hardware Acceleration
This operation is optimized for SSE2 technology for pixels of type: UINT8.
This operation supports automatic parallelization for multicore and multiprocessor systems.