Histogram Computation

The calcHist function computes the histogram of given input image.

Where, H is the array of 256 elements.

API Syntax

template<int SRC_T,int ROWS, int COLS,int NPC=1>
void calcHist(xF::Mat<SRC_T, ROWS, COLS, NPC> & _src, uint32_t *histogram)

Parameter Descriptions

The following table describes the template and the function parameters.

Table 1. calcHist Function Parameter Descriptions
Parameter Description
SRC_T Input 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
_src Input image
histogram Output array of 256 elements

Resource Utilization

The following table summarizes the resource utilization of the calcHist function for Normal Operation (1 pixel) and Resource Optimized (8 pixel) configurations, generated using Vivado HLS 2017.1 version tool for the Xilinx Xczu9eg-ffvb1156-1-i-es1 FPGA at 300 MHz for 1 pixel case and at 150 MHz for 8 pixel mode.

Table 2. calcHist Function Resource Utilization Summary
Name Resource Utilization

Normal Operation (1 pixel)

Resource Optimized (8 pixel)
BRAM_18K 2 16
DSP48E 0 0
FF 196 274
LUT 240 912
CLB 57 231

Performance Estimate

The following table summarizes a performance estimate of the calcHist function for Normal Operation (1 pixel) and Resource Optimized (8 pixel) configurations, generated using Vivado HLS 2017.1 version tool for the Xilinx Xczu9eg-ffvb1156-1-i-es1 FPGA at 300 MHz for 1 pixel and 150 MHz for 8 pixel mode.

Table 3. calcHist Function Performance Estimate Summary
Operating Mode Latency Estimate
Max (ms)
Normal Operation 6.9
Resource Optimized 1.7