background color affecting contour detection

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I have been successful in detecting contours and drawing those back on the original image.

Here is my original image:

Link to full size image There is download button in lower right

Portion of Python script where I detect contours:

image = cv2.imread("/Users/donaldkeidel/Downloads/input_template_masked.jpg")
# grayscale the image
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
# apply a Gaussian blur
blur = cv2.GaussianBlur(gray, (3, 3), 0)
# threshold the image
(t, binary) = cv2.threshold(blur, 100, 255, cv2.THRESH_BINARY)
# find contours
(_, contours, _) = cv2.findContours(binary, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
image_cropped_contoured_drawn = cv2.drawContours(image.copy(), contours, -1, (0, 255, 0), 3)
cv2.imwrite("F4GSCZQJHG7K_template_masked_contoured_exploration.jpg", image_cropped_contoured_drawn)

Here is the output image:

Link to full size image There is download button in lower right

As you can see in the image, almost all the contours were captured where the background color is a lighter gray. However, where the background is an almost black in the middle of the image, less contours were detected.

Are there some techniques that can be applied to detect more of these contours? I played with the threshold value and found that 100 works the best. I also used a few other values for the parameters in the GaussianBlur method.

Thank you.

Update:

I applied equalizeHist by doing the following:

image = cv2.imread("/Users/donaldkeidel/Downloads/input_template_masked.jpg")
# grayscale the image
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
# Histogram equalization
equ = cv2.equalizeHist(gray)
# threshold the image
(t, binary) = cv2.threshold(equ, 100, 255, cv2.THRESH_BINARY)
# find contours
(_, contours, _) = cv2.findContours(binary, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
image_cropped_contoured_drawn = cv2.drawContours(image.copy(), contours, -1, (0, 255, 0), 3)
cv2.imwrite("F4GSCZQJHG7K_template_masked_contoured_exploration.jpg", image_cropped_contoured_drawn)

The following image shows the gray scale image compared to Histogram Equalized image:

And here is image after contour detection:

Any further suggestions on how to proceed are appreciated. I like the suggestion about increasing the contrast using Histogram Equalizatioon, however, drawing contours on this image proves to be difficult. Should I preprocess the image more?