我的图片;
要求:
我无法理解如何确定轴以使图像始终保持水平。
算法:
我的代码:
//read the image
img = imread("90.jpeg")
cv::Mat contourOutput = img.clone();
// detect external contour(images will have noise, although example images doesn't have)
std::vector<std::vector<cv::Point> > contours;
cv::findContours(contourOutput, contours, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);
int largest_area = 0;
int largest_contour_index = 0;
for (size_t i = 0; i < contours.size(); i++) {
double area = contourArea(contours[i]);
// copy the largest contour index
if (area > largest_area) {
largest_area = area;
largest_contour_index = i;
}
}
//draw contours
drawContours(img, contours, largest_contour_index, Scalar(255, 0, 0),
2);
// detect minimum area rect to get the angle and centre
cv::RotatedRect box = cv::minAreaRect(cv::Mat(contours[largest_contour_index]));
// take the box angle
double angle = box.angle;
if (angle < -45) {
box.angle += 90;
}
angle = box.angle;
// create rotation matrix
cv::Mat rot_mat = cv::getRotationMatrix2D(box.center, angle, 1);
// Apply the transformation
cv::Mat rotated;
cv::warpAffine(img, rotated, rot_mat, img.size(), cv::INTER_CUBIC);
cv::Size box_size = box.size;
if (box.angle < -45.)
std::swap(box_size.width, box_size.height);
// get the cropped image
cv::Mat cropped;
cv::getRectSubPix(rotated, box_size, box.center, cropped);
// Display the image
namedWindow("image2", WINDOW_NORMAL);
imshow("image2", cropped);
waitKey(0);
想法是使用minAreaRect
计算旋转的边界框角度,然后使用getRotationMatrix2D
和warpAffine
校正图像。最后一步是如果要处理垂直图像,则旋转90度。这是之前(左)和之后(右)以及旋转角度的结果:
-39.999351501464844
38.52387619018555
1.6167902946472168
1.9749339818954468
我用Python实现了它,但您可以将相同的方法改编成C ++
代码
import cv2
import numpy as np
# Load image, grayscale, and Otsu's threshold
image = cv2.imread('4.png')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)[1]
# Compute rotated bounding box
coords = np.column_stack(np.where(thresh > 0))
angle = cv2.minAreaRect(coords)[-1]
# Determine rotation angle
if angle < -45:
angle = -(90 + angle)
else:
angle = -angle
print(angle)
# Rotate image to deskew
(h, w) = image.shape[:2]
center = (w // 2, h // 2)
M = cv2.getRotationMatrix2D(center, angle, 1.0)
rotated = cv2.warpAffine(image, M, (w, h), flags=cv2.INTER_CUBIC, borderMode=cv2.BORDER_REPLICATE)
# Vertical image so rotate to horizontal
h, w, _ = rotated.shape
if h > w:
rotated = cv2.rotate(rotated, cv2.ROTATE_90_CLOCKWISE)
cv2.imshow('rotated', rotated)
cv2.imwrite('rotated.png', rotated)
cv2.waitKey()