Finding corners of box and crop Image-CodePudding

Hey Guys I am working with numpy and opencv and want to get a image cropped by the contours of it. Here is one example what picture i want to crop by the edges,

And i want that the yellow line (rectangle) get cropped by python,

import numpy as np
import cv2
from PIL import Image


image = cv2.imread('4.png')
result = image.copy()
image = cv2.cvtColor(image, cv2.COLOR_BGR2HSV)
lower = np.array([103, 131, 70])
upper = np.array([179, 234, 255])
mask = cv2.inRange(image, lower, upper)
result = cv2.bitwise_and(result, result, mask=mask)


print(image.shape)
cv2.imshow('mask', mask)
cv2.imshow('result', result)
cv2.waitKey()

CodePudding user response：

You can opt for the LAB color space.

Now why use LAB color space over HSV?

It's easier to segment the color of your choice by analyzing the chroma channels.
There is no need to manually fix a range (unlike in HSV color space). Otsu threshold will help.

What is LAB color space?

L-channel : represents brightness value in the image
A-channel : represents variation of color between red and green
B-channel : represents variation of color between blue and yellow

th = cv2.threshold(a_component,127,255,cv2.THRESH_BINARY cv2.THRESH_OTSU)[1]
contours, hierarchy = cv2.findContours(th, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
c = max(contours, key = cv2.contourArea)

black = np.zeros((img.shape[0], img.shape[1]), np.uint8)
mask = cv2.drawContours(black,[c],0,255, -1)

result = cv2.bitwise_and(result, result, mask=mask)

Hope this is the result you were expecting