Box Filter

The xFboxfilter function performs box filtering on the input image. Box filter acts as a low-pass filter and performs blurring over the image. The xFboxfilter function or the box blur is a spatial domain linear filter in which each pixel in the resulting image has a value equal to the average value of the neighboring pixels in the image.

API Syntax

template<int BORDER_TYPE,int FILTER_TYPE, int SRC_T, int ROWS, int COLS,int NPC=1>
void xFboxfilter(xF::Mat<SRC_T, ROWS, COLS, NPC> & _src_mat,xF::Mat<SRC_T, ROWS, COLS, NPC> & _dst_mat)

Parameter Descriptions

The following table describes the template and the function parameters.:

Table 1. xFboxfilter Function Parameter Descriptions
Parameter	Description
FILTER_SIZE	Filter size. Filter size of 3(XF_FILTER_3X3), 5(XF_FILTER_5X5) and 7(XF_FILTER_7X7) are supported
BORDER_TYPE	Border Type supported is XF_BORDER_CONSTANT
SRC_T	Input and output pixel type. 8-bit, unsigned, 16-bit unsigned and 16-bit signed, 1 channel is supported (XF_8UC1)
ROWS	Maximum height of input and output image (must be a multiple of 8)
COLS	Maximum width of input and output image (must be a multiple of 8)
NPC	Number of pixels to be processed per cycle; possible options are XF_NPPC1 and XF_NPPC8 for 1 pixel and 8 pixel operations respectively.
_src_mat	Input image
_dst_mat	Output image

Resource Utilization

The following table summarizes the resource utilization of the kernel in different configurations, generated using Vivado HLS 2017.1 tool for the Xilinx Xczu9eg-ffvb1156-1-i-es1 FPGA, to process a grayscale HD (1080x1920) image.

Table 2. xFboxfilter Function Resource Utilization Summary
Operating Mode	Filter Size	Operating Frequency (MHz)	Utilization Estimate
Operating Mode	Filter Size	Operating Frequency (MHz)	BRAM_18K	DSP_48Es	FF	LUT	CLB
1 pixel	3x3	300	3	1	545	519	104
	5x5	300	5	1	876	870	189
	7x7	300	7	1	1539	1506	300
8 pixel	3x3	150	6	8	1002	1368	264
	5x5	150	10	8	1576	3183	611
	7x7	150	14	8	2414	5018	942

Performance Estimate

The following table summarizes the performance of the kernel in different configurations, as generated using Vivado HLS 2017.1 tool for the Xilinx Xczu9eg-ffvb1156-1-i-es1, to process a grayscale HD (1080x1920) image:

Table 3. xFboxfilter Function Performance Estimate Summary
Operating Mode	Operating Frequency (MHz)	Filter Size	Latency Estimate
Operating Mode	Operating Frequency (MHz)	Filter Size	Max (ms)
1 pixel	300	3x3	7.2
	300	5x5	7.21
	300	7x7	7.22
8 pixel	150	3x3	1.7
	150	5x5	1.7
	150	7x7	1.7