Gaussian Filter

The xFGaussianBlur function applies Gaussian blur on the input image. Gaussian filtering is done by convolving each point in the input image with a Gaussian kernel.

Where , are the mean values and , are the variances in x and y directions respectively. In the GaussianBlur function, values of , are considered as zeroes and the values of , are equal.

API Syntax

template<int FILTER_SIZE, int BORDER_TYPE, int SRC_T, int ROWS, int COLS, int NPC =  1>
void xFGaussianBlur(xF::Mat<SRC_T, ROWS, COLS, NPC> & src, xF::Mat<SRC_T, ROWS, COLS, NPC> & dst, float sigma)

Parameter Descriptions

The following table describes the template and the function parameters.

Table 1. xFGaussianBlur 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. Only 8-bit, unsigned, 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 values are XF_NPPC1 and XF_NPPC8 for 1 pixel and 8 pixel operations respectively.
src	Input image
dst	Output image
sigma	Standard deviation of Gaussian filter

Resource Utilization

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

Table 2. xFGaussianBlur 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	17	3641	2791	610
	5x5	300	5	27	4461	3544	764
	7x7	250	7	35	4770	4201	894
8 pixel	3x3	150	6	52	3939	3784	814
	5x5	150	10	111	5688	5639	1133
	7x7	150	14	175	7594	7278	1518

Performance Estimate

The following table summarizes a performance estimate of the Gaussian Filter in different configurations, as generated using Vivado HLS 2017.1 tool for Xilinx Xczu9eg-ffvb1156-1-i-es11 FPGA, to process a grayscale HD (1080x1920) image.

Table 3. xFGaussianBlur Function Performance Estimate Summary
Operating Mode	Filter Size	Latency Estimate
Operating Mode	Filter Size	Max Latency (ms)
1 pixel operation (300 MHz)	3x3	7.01
	5x5	7.03
	7x7	7.06
8 pixel operation (150 MHz)	3x3	1.6
	5x5	1.7
	7x7	1.74