Why is this code of Object detection using Template Matching does not run successfully

Question

The output that I get is just the reference image and no bounding box is seen in the output. I have tried this code from this website: https://www.sicara.fr/blog-technique/object-detection-template-matching

Here's the reference image Reference Image

Here are the templates: 1:

templates 2:

templates 3:

As compared to the website, using the code the output should look like this:

Expected Output:

I am expecting to have this output as discussed in the website, however, when I tried to run this code, nothing seems to be detected. Here is the code that I copied:

import cv2
import numpy as np

DEFAULT_TEMPLATE_MATCHING_THRESHOLD = 0.9

class Template:
    """
    A class defining a template
    """

    def __init__(self, image_path, label, color, matching_threshold=DEFAULT_TEMPLATE_MATCHING_THRESHOLD):
        """
        Args:
            image_path (str): path of the template image path
            label (str): the label corresponding to the template
            color (List[int]): the color associated with the label (to plot detections)
            matching_threshold (float): the minimum similarity score to consider an object is detected by template
                matching
        """
        self.image_path = image_path
        self.label = label
        self.color = color
        self.template = cv2.imread(image_path)
        self.template_height, self.template_width = self.template.shape[:2]
        self.matching_threshold = matching_threshold

image = cv2.imread("reference.jpg")

templates = [
    Template(image_path="Component1.jpg", label="1", color=(0, 0, 255), matching_threshold=0.99),
    Template(image_path="Component2.jpg", label="2", color=(0, 255, 0,) , matching_threshold=0.91),
    Template(image_path="Component3.jpg", label="3", color=(0, 191, 255), matching_threshold=0.99),


detections = []
for template in templates:
    template_matching = cv2.matchTemplate(template.template, image, cv2.TM_CCORR_NORMED)
    match_locations = np.where(template_matching >= template.matching_threshold)

    for (x, y) in zip(match_locations[1], match_locations[0]):
        match = {
            "TOP_LEFT_X": x,
            "TOP_LEFT_Y": y,
            "BOTTOM_RIGHT_X": x + template.template_width,
            "BOTTOM_RIGHT_Y": y + template.template_height,
            "MATCH_VALUE": template_matching[y, x],
            "LABEL": template.label,
            "COLOR": template.color
        }
        detections.append(match)

def compute_iou(boxA, boxB):
    xA = max(boxA["TOP_LEFT_X"], boxB["TOP_LEFT_X"])
    yA = max(boxA["TOP_LEFT_Y"], boxB["TOP_LEFT_Y"])
    xB = min(boxA["BOTTOM_RIGHT_X"], boxB["BOTTOM_RIGHT_X"])
    yB = min(boxA["BOTTOM_RIGHT_Y"], boxB["BOTTOM_RIGHT_Y"])
    interArea = max(0, xB - xA + 1) * max(0, yB - yA + 1)
    boxAArea = (boxA["BOTTOM_RIGHT_X"] - boxA["TOP_LEFT_X"] + 1) * (boxA["BOTTOM_RIGHT_Y"] - boxA["TOP_LEFT_Y"] + 1)
    boxBArea = (boxB["BOTTOM_RIGHT_X"] - boxB["TOP_LEFT_X"] + 1) * (boxB["BOTTOM_RIGHT_Y"] - boxB["TOP_LEFT_Y"] + 1)
    iou = interArea / float(boxAArea + boxBArea - interArea)
    return iou

def non_max_suppression(objects, non_max_suppression_threshold=0.5, score_key="MATCH_VALUE"):
    """
    Filter objects overlapping with IoU over threshold by keeping only the one with maximum score.
    Args:
        objects (List[dict]): a list of objects dictionaries, with:
            {score_key} (float): the object score
            {top_left_x} (float): the top-left x-axis coordinate of the object bounding box
            {top_left_y} (float): the top-left y-axis coordinate of the object bounding box
            {bottom_right_x} (float): the bottom-right x-axis coordinate of the object bounding box
            {bottom_right_y} (float): the bottom-right y-axis coordinate of the object bounding box
        non_max_suppression_threshold (float): the minimum IoU value used to filter overlapping boxes when
            conducting non-max suppression.
        score_key (str): score key in objects dicts
    Returns:
        List[dict]: the filtered list of dictionaries.
    """
    sorted_objects = sorted(objects, key=lambda obj: obj[score_key], reverse=True)
    filtered_objects = []
    for object_ in sorted_objects:
        overlap_found = False
        for filtered_object in filtered_objects:
            iou = compute_iou(object_, filtered_object)
            if iou > non_max_suppression_threshold:
                overlap_found = True
                break
        if not overlap_found:
            filtered_objects.append(object_)
    return filtered_objects
NMS_THRESHOLD = 0.2
detections = non_max_suppression(detections, non_max_suppression_threshold=NMS_THRESHOLD)
image_with_detections = image.copy()

for detection in detections:
    cv2.rectangle(
        image_with_detections,
        (detection["TOP_LEFT_X"], detection["TOP_LEFT_Y"]),
        (detection["BOTTOM_RIGHT_X"], detection["BOTTOM_RIGHT_Y"]),
        detection["COLOR"],
        2,
    )
    cv2.putText(
        image_with_detections,
        f"{detection['LABEL']} - {detection['MATCH_VALUE']}",
        (detection["TOP_LEFT_X"] + 2, detection["TOP_LEFT_Y"] + 20),
        cv2.FONT_HERSHEY_SIMPLEX, 0.5,
        detection["COLOR"], 1,
        cv2.LINE_AA,
    )

# NMS_THRESHOLD = 0.2
# detection = non_max_suppression(detections, non_max_suppression_threshold=NMS_THRESHOLD)

print("Image written to file-system: ", status)
cv2.imshow("res", image_with_detections)
cv2.waitKey(0)

this is how his final output looks like: 5

Here's my attempt in detecting the larger components, the code was able to detect them and here is the result: Result

Here are the resize templates and the original components that I wanted to detect but unfortunately can't:

1st 2nd 3rd

Answer 1

Here is a method of finding multiple matches in template matching in Python/OpenCV using your reference and smallest template. I have remove all the white padding you had around your template. My method simply draws a black rectangle over the correlation image where it matches and then repeats looking for the next best match in the modified correlation image.

I have used cv2.TM_CCORR_NORMED and a match threshold of 0.90. You have 4 of these templates showing in your reference image, so I set my search number to 4 and spacing of 10 for the non-maximum suppression by masking. You have other small items of the same shape and size, but the text on them is different. So you will need different templates for each.

Reference:

Template:

import cv2
import numpy as np

# read image
img = cv2.imread('circuit_board.jpg')

# read template
tmplt = cv2.imread('circuit_item.png')
hh, ww, cc = tmplt.shape

# set arguments
match_thresh = 0.90               # stopping threshold for match value
num_matches = 4                   # stopping threshold for number of matches
match_radius = 10                 # approx radius of match peaks
match_radius2 = match_radius//2

# get correlation surface from template matching
corrimg = cv2.matchTemplate(img,tmplt,cv2.TM_CCORR_NORMED)
hc, wc = corrimg.shape

# get locations of all peaks higher than match_thresh for up to num_matches
imgcopy = img.copy()
corrcopy = corrimg.copy()
for i in range(0, num_matches):
    # get max value and location of max
    min_val, max_val, min_loc, max_loc = cv2.minMaxLoc(corrcopy)
    x1 = max_loc[0]
    y1 = max_loc[1]
    x2 = x1 + ww
    y2 = y1 + hh
    loc = str(x1) + "," + str(y1)
    if max_val > match_thresh:
        print("match number:", i+1, "match value:", max_val, "match x,y:", loc)
        # draw draw white bounding box to define match location
        cv2.rectangle(imgcopy, (x1,y1), (x2,y2), (255,255,255), 1)
        # insert black rectangle over copy of corr image so not find that match again
        corrcopy[y1-match_radius2:y1+match_radius2, x1-match_radius2:x1+match_radius2] = 0
        i = i + 1
    else:
        break
    
# save results
# power of 4 exaggeration of correlation image to emphasize peaks
cv2.imwrite('circuit_board_multi_template_corr.png', (255*cv2.pow(corrimg,4)).clip(0,255).astype(np.uint8))
cv2.imwrite('circuit_board_multi_template_corr_masked.png', (255*cv2.pow(corrcopy,4)).clip(0,255).astype(np.uint8))
cv2.imwrite('circuit_board_multi_template_match.png', imgcopy)


# show results
# power of 4 exaggeration of correlation image to emphasize peaks
cv2.imshow('image', img)
cv2.imshow('template', tmplt)
cv2.imshow('corr', cv2.pow(corrimg,4))
cv2.imshow('corr masked', cv2.pow(corrcopy,4))
cv2.imshow('result', imgcopy)
cv2.waitKey(0)
cv2.destroyAllWindows()

Original Correlation Image:

Modified Correlation Image after 4 matches:

Matches Marked on Input as White Rectangles:

Match Locations:

match number: 1 match value: 0.9982172250747681 match x,y: 128,68
match number: 2 match value: 0.9762057065963745 match x,y: 128,90
match number: 3 match value: 0.9755787253379822 match x,y: 128,48
match number: 4 match value: 0.963689923286438 match x,y: 127,107