Started analysis script with single example taken from stackoverflow as a starting point. Had to modify it to support opencv 4.x but got it to run. Finds holes.

fourcell/.gitignore

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+env

fourcell/README.md

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+# Four Cell Script
+
+Two scripts:
+
+1. Analyzes a calibration sheet on the plotter to generate a template.
+2. Takes cells and inserts them into the template 4 at a time.
+
+
+## Analysis Steps
+
+1. Locate positions of 6 hole punches
+2. Orient to square position
+3. Find all 4 fiducials
+4. Calculate their position relative to the hole punches
+5. Create a template 
+6. Use the template-filling script to recreate calibration page as a proof to be checked on a lightbox

fourcell/analyze.py

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+import sys
+import cv2
+import numpy as np
+
+if len(sys.argv) < 2:
+	print('Please provide path to image for analysis')
+	exit(1)
+
+if len(sys.argv) < 3:
+	print('Please provide path to template file to create')
+	exit(2)
+
+scanImage = sys.argv[-2]
+templateFile = sys.argv[-1]
+
+print(f'Analyzing {scanImage} and creating {templateFile}')
+
+#https://stackoverflow.com/questions/51456660/opencv-detecting-drilled-holes

fourcell/notes/example1.py

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+#https://stackoverflow.com/questions/51456660/opencv-detecting-drilled-holes
+
+import cv2
+import numpy as np
+
+img = cv2.imread("./example1.jpg")
+# cv2.imshow("original", img)
+
+gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
+# cv2.imshow("gray", gray)
+
+blur = cv2.medianBlur(gray, 31)
+# cv2.imshow("blur", blur)
+
+ret, thresh = cv2.threshold(blur, 127, 255, cv2.THRESH_OTSU)
+# cv2.imshow("thresh", thresh)
+
+canny = cv2.Canny(thresh, 75, 200)
+# cv2.imshow('canny', canny)
+
+contours, hierarchy = cv2.findContours(canny, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)
+
+contour_list = []
+for contour in contours:
+    approx = cv2.approxPolyDP(contour, 0.01 * cv2.arcLength(contour, True), True)
+    area = cv2.contourArea(contour)
+    if 5000 < area < 15000:
+        contour_list.append(contour)
+
+msg = "Total holes: {}".format(len(approx)//2)
+cv2.putText(img, msg, (20, 40), cv2.FONT_HERSHEY_PLAIN, 2, (0, 0, 255), 2, cv2.LINE_AA)
+
+cv2.drawContours(img, contour_list, -1, (0, 255, 0), 2)
+cv2.imshow('Objects Detected', img)
+
+cv2.imwrite("detected_holes.png", img)
+
+cv2.waitKey(0)

fourcell/requirements.txt

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+opencv-python