Pixel-Wise Subtraction

ThexFsubtractfunction performs the pixel-wise subtraction between two input images and returns the output image.

Iout(x, y) = Iin1(x, y) - Iin2(x, y)

Where:

  • Iout(x, y) is the intensity of the output image at (x, y) position
  • Iin1(x, y) is the intensity of the first input image at (x, y) position
  • Iin2(x, y) is the intensity of the second input image at (x, y) position.

XF_CONVERT_POLICY_TRUNCATE: Results are the least significant bits of the output operand, as if stored in two’s complement binary format in the size of its bit-depth.

XF_CONVERT_POLICY_SATURATE: Results are saturated to the bit depth of the output operand.

API Syntax

template void xFsubtract ( xF::Mat src1, xF::Mat src2, xF::Mat dst )

Parameter Descriptions

The following table describes the template and the function parameters.

Table 1.xFsubtract Function Parameter Descriptions
Parameter Description
POLICY_TYPE Type of overflow handling. It can be either, XF_CONVERT_POLICY_SATURATE or XF_CONVERT_POLICY_TRUNCATE.
SRC_T pixel type. Options are XF_8UC1 and XF_16SC1.
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.
src1 Input image
src2 Input image
dst Output image

Resource Utilization

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

Table 2.xFsubtract Function Resource Utilization Summary
Operating Mode

Operating Frequency

(MHz)

 Utilization Estimate
BRAM_18K DSP_48Es FF LUT CLB
1 pixel 300 0 0 62 53 11
8 pixel 150 0 0 59 13 21

Performance Estimate

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

Table 3.xFsubtract Function Performance Estimate Summary
Operating Mode Latency Estimate
Max Latency (ms)
1 pixel operation (300 MHz) 6.9
8 pixel operation (150 MHz) 1.7