Crop Exact Document Paper From Image By Removing Black Border From Photos In Java/python

I have taken some pictures of index cards but now I have the problem that the photographing was not perfect of course and there is a black border on each photo. I would like to cro

Solution 1:

The idea is to threshold the image to obtain a binary image then find contours and sort using contour area. The largest contour should be the index card. We can then apply a four point perspective transform to obtain a birds eye view of the image. Here's the results:

Binary image

Result

The result is dark so to increase the contrast look at Automatic contrast and brightness adjustment of a color photo of a sheet of paper with OpenCV. Also it's slightly skewed so you should perform skew correction. Take a look at Python OpenCV skew correction, How to de-skew an image, and Detect image orientation angle based on text direction

I'll leave these steps to you :)

Code

from imutils.perspective import four_point_transform
import cv2
import numpy

# Load image, grayscale, Gaussian blur, Otsu's threshold
image = cv2.imread("1.jpg")
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray, (5,5), 0)
thresh = cv2.threshold(blur, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)[1]

# Find contours and sort for largest contour
cnts = cv2.findContours(thresh, cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] iflen(cnts) == 2else cnts[1]
cnts = sorted(cnts, key=cv2.contourArea, reverse=True)
displayCnt = Nonefor c in cnts:
    # Perform contour approximation
    peri = cv2.arcLength(c, True)
    approx = cv2.approxPolyDP(c, 0.02 * peri, True)
    iflen(approx) == 4:
        displayCnt = approx
        break# Obtain birds' eye view of image
warped = four_point_transform(image, displayCnt.reshape(4, 2))

cv2.imshow("thresh", thresh)
cv2.imshow("warped", warped)
cv2.imshow("image", image)
cv2.imwrite("thresh.png", thresh)
cv2.imwrite("warped.png", warped)
cv2.imwrite("image.png", image)
cv2.waitKey()

Solution 2:

Maybe, this previous post's answer is helpful https://stackoverflow.com/a/21568925/9851541 Further, this may also prove helpful

from PIL import ImageChops

     deftrim(im, border):
         bg = Image.new(im.mode, im.size, border)
         diff = ImageChops.difference(im, bg)
         bbox = diff.getbbox()
         if bbox:
             return im.crop(bbox)
         else:
             # found no contentraise ValueError("cannot trim; image was empty")