在无网格图像 Python Opencv 上画线

Question

I have an image like this below. [![enter image description here][2]][2] I try to add both vertical and horizontal lines between rows and columns. I succeeded in adding the horizontal ones using the code provided [here][1]. But I failed to add the vertical ones. Can anyone help to point out what went wrong with my code?

import cv2
import numpy as np
import matplotlib.pyplot as plt
file = r"C:/Users/gaojia/Dropbox/Projects/Parking_lot/Community_Group_Buying/scripts/test_2.png"
# read image
img = cv2.imread(file)
hh, ww = img.shape[:2]

# convert to grayscale 
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

# threshold gray image
thresh = cv2.threshold(gray, 254, 255, cv2.THRESH_BINARY)[1]

# count number of non-zero pixels in each row
count = np.count_nonzero(thresh, axis=0)

# threshold count at ww (width of image)
count_thresh = count.copy()
count_thresh[count==hh] = 255
count_thresh[count<hh] = 0
count_thresh = count_thresh.astype(np.uint8)

# get contours
contours = cv2.findContours(count_thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
contours = contours[0] if len(contours) == 2 else contours[1]

# loop over contours and get bounding boxes and ycenter and draw horizontal line at ycenter
result = img.copy()
for cntr in contours:
    x,y,w,h = cv2.boundingRect(cntr)
    xcenter = x+w//2
    cv2.line(result, (xcenter,0), (xcenter, hh-1), (0, 0, 0), 2)


# display results
cv2.imshow("THRESHOLD", thresh)
cv2.imshow("RESULT", result)
cv2.waitKey(0)

The code above draws only one vertical line at the far left of the image. I removed the vertical line in the original image, but the result remains the same.

-----------------------EDIT-----------------------------

As is in the first answer, I realized that the input for findContours() should not be a one-dimensional array. I thus replaced the following code:

# count number of non-zero pixels in each row
count = np.count_nonzero(thresh, axis=0)

# threshold count at ww (width of image)
count_thresh = count.copy()
count_thresh[count==hh] = 255
count_thresh[count<hh] = 0
count_thresh = count_thresh.astype(np.uint8)

with:

# find row index with any value equals 0
row_zero = np.nonzero(np.any(thresh == 0, axis=1))[0]
# replace values in column with any 0 with 0.
thresh[row_zero, :] =  0

This adds the vertical lines between columns of text. [1]: Python & OpenCV: How to add lines to gridless table [2]: https://i.stack.imgur.com/YnPns.png

Answer 1

Your issue is that count is one dimensional no matter whether along axis 0 or 1. So you have to transpose the x,y and w,h in your bounding boxes to use as you did in Python/OpenCV.

Input:

import cv2
import numpy as np

# read image
img = cv2.imread("gridless_table.png")
hh, ww = img.shape[:2]

# convert to grayscale 
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

# threshold gray image
thresh = cv2.threshold(gray, 254, 255, cv2.THRESH_BINARY)[1]

# count number of non-zero pixels in each column
count = np.count_nonzero(thresh, axis=0)

# threshold count at hh (height of image)
count_thresh = count.copy()
count_thresh[count==hh] = 255
count_thresh[count<hh] = 0
count_thresh = count_thresh.astype(np.uint8)

# get contours
contours = cv2.findContours(count_thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
contours = contours[0] if len(contours) == 2 else contours[1]

# loop over contours and get bounding boxes and xcenter and draw vertical line at ycenter
result = img.copy()
for cntr in contours:
    # must transpose x,y and w,h since count is one-dimensional but represents each column
    y,x,h,w = cv2.boundingRect(cntr)
    print(x,y,w,h)
    xcenter = x+w//2
    cv2.line(result, (xcenter,0), (xcenter, hh-1), (0, 0, 0), 2)

# save results
cv2.imwrite("gridless_table_lines.png", result)

# display results
cv2.imshow("THRESHOLD", thresh)
cv2.imshow("RESULT", result)
cv2.waitKey(0)

Result: