VXLIB_fastCorners_i8u

Functions
VXLIB_STATUS	VXLIB_fastCorners_i8u (const uint8_t src[], const VXLIB_bufParams2D_t *src_addr, uint32_t corners[], uint8_t strengths[], uint32_t corners_capacity, uint8_t strength_thresh, uint32_t *num_corners, uint8_t do_nonmax, uint8_t scratch[], uint32_t scratch_size)
VXLIB_STATUS	VXLIB_fastCorners_i8u_checkParams (const uint8_t src[], const VXLIB_bufParams2D_t *src_addr, const uint32_t corners[], const uint8_t strengths[], uint32_t corners_capacity, uint8_t strength_thresh, const uint32_t *num_corners, uint8_t do_nonmax, const uint8_t scratch[], uint32_t scratch_size)

Detailed Description

Function Documentation

VXLIB_fastCorners_i8u()

VXLIB_STATUS VXLIB_fastCorners_i8u	(	const uint8_t	src[],
		const VXLIB_bufParams2D_t *	src_addr,
		uint32_t	corners[],
		uint8_t	strengths[],
		uint32_t	corners_capacity,
		uint8_t	strength_thresh,
		uint32_t *	num_corners,
		uint8_t	do_nonmax,
		uint8_t	scratch[],
		uint32_t	scratch_size
	)

Description:

Computes the corners in an 8 bit image using the FAST9 algorithm.

Method:

FAST9 algorithm, with optional non-maximum suppression.

Parameters

[in]	src[]	Pointer to array containing input image (UQ8.0)
[in]	src_addr[]	Pointer to structure containing dimensional information of src
[out]	corners[]	Pointer to array containing corner keypoint list (UQ32.0)
[out]	strengths[]	Pointer to array containing strength list corresponding to corners[] (UQ8.0)
[in]	corners_capacity	Number of keypoints allocated in the corners buffer.
[in]	strength_thresh	Threshold on difference between intensity of the central pixel and pixels on the Bresenham's circlue of radius 3.
[out]	*num_corners	Total number of corners found in the image.
[in]	do_nonmax	Flag to enable (1) or disable (0) nonmax suppression and strength calculation.
[in]	scratch[]	Pointer to scratch buffer (UQ8.0)
[in]	scratch_size	Size of the scratch buffer (for parameter checking)

Assumptions:

• I/O buffer pointers are assumed to be not aliased.
• The minimum image width and height are both 7.
• Corners can not be detected in the 3 pixels that make up the image border.
• Each 32-bit word in corners[] array is composed of 2 16-bit half words representing x and y coordinates, such that corners[i] = (y(i) << 16) | x(i);
• The scratch buffer should be 8 byte aligned.
• The strengths pointer may be set to NULL if only the feature locations are needed AND do_nonmax is set to 0.
• If do_nonmax == 0
  • The strengths[] pointer may be set to NULL.
  • If the strengths[] pointer is set to NULL, the scratch buffer size should be at least 64 bytes.
  • If the strengths[] pointer is not set to NULL, the scratch buffer size should be at least 463 bytes.
• If do_nonmax == 1
  • The strengths[] pointer must not be set to NULL, since strength values are needed to perform the non-maximum suppression.
  • The scratch buffer should be at least MAX(463, (4 * src_addr->dim_x) + num_corners_in + 30) bytes.

Performance Considerations:

• For best performance, the following parameter settings are recommended:
  • Set widths equal each other and equal to strides (allows processing over whole image in single loop)

VXLIB_fastCorners_i8u_checkParams()

VXLIB_STATUS VXLIB_fastCorners_i8u_checkParams	(	const uint8_t	src[],
		const VXLIB_bufParams2D_t *	src_addr,
		const uint32_t	corners[],
		const uint8_t	strengths[],
		uint32_t	corners_capacity,
		uint8_t	strength_thresh,
		const uint32_t *	num_corners,
		uint8_t	do_nonmax,
		const uint8_t	scratch[],
		uint32_t	scratch_size
	)

Description:

Checks the parameters for programming errors for the VXLIB_fastCorners_i8u function.

Method:

The following checks are made:

• There shall be no NULL pointers (exception: strenghts can be NULL if do_nonmax == 0)
• The strides of the image shall be equal to or greater than the x dimension
• The scratch_size shall be checked according to the parameter settings listed in the function description of the VXLIB_fastCorners_i8u function.

Parameters

[in]	src[]	Pointer to array containing input image (UQ8.0)
[in]	src_addr[]	Pointer to structure containing dimensional information of src
[out]	corners[]	Pointer to array containing corner keypoint list (UQ32.0)
[out]	strengths[]	Pointer to array containing strength list corresponding to corners[] (UQ8.0)
[in]	corners_capacity	Number of keypoints allocated in the corners buffer.
[in]	strength_thresh	Threshold on difference between intensity of the central pixel and pixels on the Bresenham's circlue of radius 3.
[out]	*num_corners	Total number of corners found in the image.
[in]	do_nonmax	Flag to enable (1) or disable (0) nonmax suppression and strength calculation.
[in]	scratch[]	Pointer to scratch buffer (UQ8.0)
[in]	scratch_size	Size of the scratch buffer (for parameter checking)