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Detection and removal of circular artifacts from photographs

Description

Reflecting flashlight from dust, snowflakes or raindrops can produce irritating circular artifacts. For its detecting and removing we propose process, where we use improved circle detection besides using houghCircles function. For removing detected artifacts we use morphological reduction.

Functions used

adaptiveThreshold, Canny, HoughCircles, findContours, fitEllipse, ImReconstruct

Process

Greyscale input image with circular artifacts.
Output image.

Limitation: Minimal circle size (15px )- Maximal circle size(30px)

  1. Preprocessing – Adaptive threshold
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    medianBlur()
    adaptiveThreshold()
    OutputImg := InputImg + FilteredImg
  2. Detection with HoughCircles
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    Canny()
    GaussianBlur()
    HoughCircles()
    Accept/ignore circles (based on size)
  3. Detection with Morphological reconstruction and contour analysis
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    mask := InputImg
    marker := InputImg – degreeOfMorphreduct
    marker := inv(marker)
    morphologicalReconstruction(marker, mask)
    differenceImg := marker2 – marker1
    differenceImg := medianBlur(differenceImg)
    differenceImg := threshold(differenceImg)
    contour[] = findContours (differenceImg)
    ellipse[i] := fitEllipse(contour[i])
    accept/ignore circles (based on size and ellipse axes)
    draw white ellipse[i]
    draw black contour[i]
    crop Regions Of Interest
    opening(regionOfInterest[i])
    if countNonZero(regionOfInterest[i]) > threshold then accept; else ignore;
  4. Result