FAST Corners

Detect FAST corners in an image, usually used in keypoint tracking. More...

Data Structures
struct	VPIFASTCornerDetectorParams
	Structure that defines the parameters for vpiSubmitFASTCornerDetector. More...

Functions
VPIStatus	vpiInitFASTCornerDetectorParams (VPIFASTCornerDetectorParams *params)
	Initializes VPIFASTCornerDetectorParams with default values. More...
VPIStatus	vpiSubmitFASTCornerDetector (VPIStream stream, uint64_t backend, VPIImage input, VPIArray outCorners, const VPIFASTCornerDetectorParams *params, VPIBorderExtension border)
	Submits a FAST Corner Detector operation to the stream. More...

Detailed Description

Detect FAST corners in an image, usually used in keypoint tracking.

Refer to FAST Corners Detector for more details and usage examples.

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Data Structure Documentation

VPIFASTCornerDetectorParams

struct VPIFASTCornerDetectorParams

Structure that defines the parameters for vpiSubmitFASTCornerDetector.

Definition at line 81 of file FASTCorners.h.

Collaboration diagram for VPIFASTCornerDetectorParams:

Data Fields
int32_t	circleRadius	Circle radius around a pixel to check if it is a corner. The following circle radii are supported, correlating each radius with the number of pixels in the circle: Circle radius Number of pixels in the circle 1 8 2 12 3 16 Must be 1, 2 or 3.
int32_t	arcLength	Arc length in pixels over the circle to check central pixel is a corner. Arc length is the minimum number of contiguous pixels in the circle that are either brighter (have higher intensity values) or darker (have lower intensity values) than the central pixel, plus or minus a threshold, respectively, to mark it as a corner. For VPI_BACKEND_CPU, it must be in the valid range from 1 to the number of pixels in the circle. For VPI_BACKEND_CUDA, it must be either 5, 7 or 9 according to the circle radius as: Circle radius Arc length 1 5 2 7 3 9
float	intensityThreshold	Threshold to select a pixel as being part of the arc in circle around a keypoint candidate. Intensity threshold is used to check if a pixel in the circle is either brighter (has higher intensity value) or darker (has lower intensity value) than the central pixel. This check is used in the arc calculation to determine if a pixel is in the arc or not.
int8_t	nonMaxSuppression	Whether to apply non-maximum suppression to remove corners too close together. If not '0', it activates non-maximum suppression (NMS) for the FAST corner detector algorithm. The NMS for FAST suppresses pixels in a 1-ring neighborhood by increasing the intensity threshold value and removing corner pixels that fail the arc length calculation, keeping the single pixel in the neighborhood that survives. If '0', it deactivates the non-maximum suppression.

Function Documentation

vpiInitFASTCornerDetectorParams()

VPIStatus vpiInitFASTCornerDetectorParams

(

VPIFASTCornerDetectorParams *

params

)

#include </opt/nvidia/vpi2/include/vpi/algo/FASTCorners.h>

Initializes VPIFASTCornerDetectorParams with default values.

Default values are:

• circleRadius: 3
• arcLength: 9
• intensityThreshold: 10
• nonMaxSuppression: 1

Return values

VPI_ERROR_INVALID_ARGUMENT	params is NULL.
VPI_SUCCESS	Operation executed successfully.

vpiSubmitFASTCornerDetector()

VPIStatus vpiSubmitFASTCornerDetector	(	VPIStream	stream,
		uint64_t	backend,
		VPIImage	input,
		VPIArray	outCorners,
		const VPIFASTCornerDetectorParams *	params,
		VPIBorderExtension	border
	)

#include </opt/nvidia/vpi2/include/vpi/algo/FASTCorners.h>

Submits a FAST Corner Detector operation to the stream.

Parameters

[in]	stream	The stream where the operation will be queued in. Must not be NULL. Stream must have enabled the backends that will execute the algorithm.
[in]	backend	Backend that will execute the algorithm. Valid values: VPI_BACKEND_CPU VPI_BACKEND_CUDA
[in]	input	Input image from where the FAST corners will be extracted. Must not be NULL. Image must have enabled the backends that will execute the algorithm. The accepted image formats are: VPI_IMAGE_FORMAT_Y8 VPI_IMAGE_FORMAT_Y16 VPI_IMAGE_FORMAT_Y8_ER VPI_IMAGE_FORMAT_Y16_ER VPI_IMAGE_FORMAT_U8 VPI_IMAGE_FORMAT_S8 VPI_IMAGE_FORMAT_U16 VPI_IMAGE_FORMAT_S16
[out]	outCorners	Array that will receive the detected corners. Array size is updated with the number of corners found. Must not be NULL. It must have type VPI_ARRAY_TYPE_KEYPOINT_F32. Array must have enabled the backends that will execute the algorithm.
[in]	params	Pointer to a VPIFASTCornerDetectorParams. It defines the parameters for this algorithm invocation. These parameters can vary in every call and will be copied internally. Thus there is no need to keep the parameters object around. If NULL, use the defaults given by vpiInitFASTCornerDetectorParams.
[in]	border	How to handle pixels outside image boundaries. The accepted border extensions are: VPI_BORDER_ZERO VPI_BORDER_CLAMP VPI_BORDER_REFLECT VPI_BORDER_MIRROR VPI_BORDER_LIMITED (ignore pixels with circle going outside image boundaries)

Return values

VPI_ERROR_INVALID_ARGUMENT	stream is NULL.
VPI_ERROR_INVALID_ARGUMENT	input or outCorners are NULL.
VPI_ERROR_INVALID_ARGUMENT	Circle radius in params outside valid range.
VPI_ERROR_INVALID_ARGUMENT	Arc length in params outside valid range.
VPI_ERROR_INVALID_ARGUMENT	Intensity threshold in params outside valid range.
VPI_ERROR_INVALID_ARRAY_TYPE	Invalid outCorners array type.
VPI_ERROR_INVALID_IMAGE_FORMAT	Unsupported input format.
VPI_ERROR_INVALID_OPERATION	The needed backends aren't enabled in stream, input or outCorners.
VPI_SUCCESS	Operation executed successfully.