使用opencv從圖片中裁剪出任意形狀的四邊形
阿新 • • 發佈:2019-01-02
寫在前面:之前是先得到任意四邊形的最小外接矩形,再使用opencv進行裁剪,但是這樣會引入噪聲。所以在此記錄下,如何直接裁剪原任意四邊形區域。
思路:
1.計算要裁剪區域四邊形的相對水平方向的旋轉角度;
2.將原圖旋轉該角度,以使得要裁剪的區域旋轉到水平方向;
3.將要裁剪區域的座標做相應的轉換,轉換為旋轉後的座標;
4.對該區域進行裁剪。
# -*- coding:utf-8 -*- import cv2 from math import * import numpy as np import time,math import os import re '''旋轉影象並剪裁''' def rotate( img, # 圖片 pt1, pt2, pt3, pt4, newImagePath ): print pt1,pt2,pt3,pt4 withRect = math.sqrt((pt4[0] - pt1[0]) ** 2 + (pt4[1] - pt1[1]) ** 2) # 矩形框的寬度 heightRect = math.sqrt((pt1[0] - pt2[0]) ** 2 + (pt1[1] - pt2[1]) **2) print withRect,heightRect angle = acos((pt4[0] - pt1[0]) / withRect) * (180 / math.pi) # 矩形框旋轉角度 print angle if pt4[1] > pt1[1]: print "順時針旋轉" else: print "逆時針旋轉" angle = -angle height = img.shape[0] # 原始影象高度 width = img.shape[1] # 原始影象寬度 rotateMat = cv2.getRotationMatrix2D((width / 2, height / 2), angle, 1) # 按angle角度旋轉影象 heightNew = int(width * fabs(sin(radians(angle))) + height * fabs(cos(radians(angle)))) widthNew = int(height * fabs(sin(radians(angle))) + width * fabs(cos(radians(angle)))) rotateMat[0, 2] += (widthNew - width) / 2 rotateMat[1, 2] += (heightNew - height) / 2 imgRotation = cv2.warpAffine(img, rotateMat, (widthNew, heightNew), borderValue=(255, 255, 255)) # 旋轉後圖像的四點座標 [[pt1[0]], [pt1[1]]] = np.dot(rotateMat, np.array([[pt1[0]], [pt1[1]], [1]])) [[pt3[0]], [pt3[1]]] = np.dot(rotateMat, np.array([[pt3[0]], [pt3[1]], [1]])) [[pt2[0]], [pt2[1]]] = np.dot(rotateMat, np.array([[pt2[0]], [pt2[1]], [1]])) [[pt4[0]], [pt4[1]]] = np.dot(rotateMat, np.array([[pt4[0]], [pt4[1]], [1]])) # 處理反轉的情況 if pt2[1] > pt4[1]: pt2[1],pt4[1] = pt4[1],pt2[1] if pt1[0] > pt3[0]: pt1[0],pt3[0] = pt3[0],pt1[0] imgOut = imgRotation[int(pt2[1]):int(pt4[1]), int(pt1[0]):int(pt3[0])] cv2.imwrite(newImagePath, imgOut) # 裁減得到的旋轉矩形框 return imgRotation # rotated image # 根據四點畫原矩形 def drawRect(img,pt1,pt2,pt3,pt4,color,lineWidth): cv2.line(img, pt1, pt2, color, lineWidth) cv2.line(img, pt2, pt3, color, lineWidth) cv2.line(img, pt3, pt4, color, lineWidth) cv2.line(img, pt1, pt4, color, lineWidth) # 讀出檔案中的座標值 def ReadTxt(directory,imageName,last): fileTxt = last # txt檔名 getTxt = open(fileTxt, 'r') # 開啟txt檔案 lines = getTxt.readlines() length = len(lines) for i in range(0,length): items = lines[i].split(',') pt1 = [int(items[0]), int(items[1])] pt4 = [int(items[2]), int(items[3])] pt3 = [int(items[4]), int(items[5])] pt2 = [int(items[6]), int(items[7])] imgSrc = cv2.imread(imageName) rotate(imgSrc,pt1,pt2,pt3,pt4,str(i)+'_'+imageName) if __name__=="__main__": directory = "." last = 'image_1210.txt' imageName = "image_1210.jpg" ReadTxt(directory,imageName,last)