[英]Python OpenCV: Crop image to contents, and make background transparent
我有以下图片:
我想将图像裁剪为实际内容,然后使背景(后面的空白区域)透明。 我看到以下问题: How to crop image based on contents (Python & OpenCV)? ,在查看答案并尝试之后,我得到了以下代码:
img = cv.imread("tmp/"+img+".png")
mask = np.zeros(img.shape[:2],np.uint8)
bgdModel = np.zeros((1,65),np.float64)
fgdModel = np.zeros((1,65),np.float64)
rect = (55,55,110,110)
cv.grabCut(img,mask,rect,bgdModel,fgdModel,5,cv.GC_INIT_WITH_RECT)
mask2 = np.where((mask==2)|(mask==0),0,1).astype('uint8')
img = img*mask2[:,:,np.newaxis]
plt.imshow(img),plt.colorbar(),plt.show()
这不是我要搜索的结果,预期结果:
这是在 Python/OpenCV 中执行此操作的一种方法。
正如我在评论中提到的,您提供的图像在牛周围有一个白色圆圈,然后是透明背景。 我已将背景设为全白作为我的输入。
输入:
import cv2
import numpy as np
# read image
img = cv2.imread('cow.png')
# convert to grayscale
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
# invert gray image
gray = 255 - gray
# threshold
thresh = cv2.threshold(gray,0,255,cv2.THRESH_BINARY)[1]
# apply close and open morphology to fill tiny black and white holes and save as mask
kernel = np.ones((3,3), np.uint8)
mask = cv2.morphologyEx(thresh, cv2.MORPH_CLOSE, kernel)
mask = cv2.morphologyEx(mask, cv2.MORPH_OPEN, kernel)
# get contours (presumably just one around the nonzero pixels)
contours = cv2.findContours(mask, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
contours = contours[0] if len(contours) == 2 else contours[1]
cntr = contours[0]
x,y,w,h = cv2.boundingRect(cntr)
# make background transparent by placing the mask into the alpha channel
new_img = cv2.cvtColor(img, cv2.COLOR_BGR2BGRA)
new_img[:, :, 3] = mask
# then crop it to bounding rectangle
crop = new_img[y:y+h, x:x+w]
# save cropped image
cv2.imwrite('cow_thresh.png',thresh)
cv2.imwrite('cow_mask.png',mask)
cv2.imwrite('cow_transparent_cropped.png',crop)
# show the images
cv2.imshow("THRESH", thresh)
cv2.imshow("MASK", mask)
cv2.imshow("CROP", crop)
cv2.waitKey(0)
cv2.destroyAllWindows()
阈值图像:
面具:
透明背景的裁剪结果:
鉴于要转换为透明的背景的 BGR 通道为白色(如您的图像) ,您可以执行以下操作:
import cv2
import numpy as np
img = cv2.imread("cat.png")
img[np.where(np.all(img == 255, -1))] = 0
img_transparent = cv2.cvtColor(img, cv2.COLOR_BGR2BGRA)
img_transparent[np.where(np.all(img == 0, -1))] = 0
cv2.imshow("transparent.png", img_transparent)
输入图像:
Output 图片:
我们可以通过点击第二张图片来判断它是透明的; 透明背景将显示为灰色(至少在 Firefox 中) 。
对我有用的是:
original_image = cv2.imread(path)
#Converting the bgr image to an image with the alpha channel
original_image = cv2.cvtColor(original_image, cv2.BGR2BGRA)
#Transforming every alpha pixel to a transparent pixel.
original_image[np.where(np.all(original_image == 255, -1))] = 0
然后写入图像。
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