如何使用OpenCV从图像中提取身份证件感兴趣区域？

Question

I am trying to segment this image because I need only to obtain the document.

Applying some filters I got this result:

I am trying to get the outline of the white rectangle but I get this result:

Anyone have any idea how to do better?

this is my code:/

import cv2

image = cv2.imread('roberto.jpg')

image = cv2.cvtColor(image, cv2.COLOR_BGR2RGB)
gray = cv2.cvtColor(image, cv2.COLOR_RGB2GRAY)

_, binary = cv2.threshold(gray, 225, 255, cv2.THRESH_BINARY_INV)
cv2.imshow('test', binary)
cv2.waitKey(0)

contours, hierarchy = cv2.findContours(binary, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)[-2:]
idx = 0 
for cnt in contours:
    idx += 1
    x,y,w,h = cv2.boundingRect(cnt)
    roi=binary[y:y+h,x:x+w]
    cv2.rectangle(image,(x,y),(x+w,y+h),(200,0,0),2)
cv2.imshow('img',image)
cv2.waitKey(0) 

Answer 1

You're almost there, you just need to obtain the x,y,w,h bounding rectangle coordinates using cv2.boundingRect then you can extract/save the ROI using Numpy slicing. Here's the result

import cv2

# Load image, grayscale, threshold
image = cv2.imread('1.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray, (3,3), 0)
thresh = cv2.threshold(gray, 225, 255, cv2.THRESH_BINARY_INV)[1]

# Get bounding box and extract ROI
x,y,w,h = cv2.boundingRect(thresh)
ROI = image[y:y+h, x:x+w]

cv2.imshow('thresh', thresh)
cv2.imshow('ROI', ROI)
cv2.waitKey()