[Halcon vision] Fourier transform of image

         Definition of Fourier transform ： Fourier transform is a transformation method from time domain to frequency domain . Generally speaking , Is to put the image in the current space , Change to a space that reflects the frequency of something .

         The use of Fourier transform ： Generally, the analysis of pixels with high frequency , And noise removal .

         Characteristics of frequency diagram ： In the center of the image is the frequency 0 The origin of , From inside to outside, the frequency is getting higher and higher . among , Where the grayscale changes violently , Corresponding to high-frequency components , Such as area edge , Where the gray change is not obvious , Corresponding to low-frequency components , Such as regional center .

* Image Reading 
read_image (Image, 'printer_chip/printer_chip_01')

* The Fourier transform 
fft_image (Image, ImageFFT)

* Regional Center 
area_center (ImageFFT, Area, Row, Column)

* A circle 1
gen_circle (Circle1, Row, Column, 200)

* A circle 2
gen_circle (Circle2, Row, Column, 1000)

* Difference between two circles 
difference (Circle2, Circle1, RegionDifference)

* Shielding area 
paint_region (RegionDifference, ImageFFT, ImageResult, 0, 'fill')

* Fourier inverse transform 
fft_image_inv (ImageResult, ImageFFTInv)