如何从图像中裁剪或删除白色背景

Question

我试图使用OpenCV和Python比较图像。

考虑这些图像：

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两者都有一双相同的鞋子，设置为白色背景。唯一的区别是第一个背景比第二个背景更高。

我想知道如何以编程方式裁剪两者的白色背景，以便我只剩下这双鞋。

我必须补充一点，我不可能手动裁剪背景。

Answer 1

您在评论中要求：The shoes are on a white background. I would like to completely get rid of the border; as in be left with a rectangular box with either a white or a transparent background, having the length and width of the shoes in the picture.

然后我的步骤裁剪目标区域：

1. 转换为灰色和阈值
2. 变形去除噪音
3. 找到最大面积轮廓
4. 裁剪并保存

#!/usr/bin/python3
# Created by Silencer @ Stackoverflow 
# 2018.01.23 14:41:42 CST
# 2018.01.23 18:17:42 CST
import cv2
import numpy as np

## (1) Convert to gray, and threshold
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
th, threshed = cv2.threshold(gray, 240, 255, cv2.THRESH_BINARY_INV)

## (2) Morph-op to remove noise
kernel = cv2.getStructuringElement(cv2.MORPH_ELLIPSE, (11,11))
morphed = cv2.morphologyEx(threshed, cv2.MORPH_CLOSE, kernel)

## (3) Find the max-area contour
cnts = cv2.findContours(morphed, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[-2]
cnt = sorted(cnts, key=cv2.contourArea)[-1]

## (4) Crop and save it
x,y,w,h = cv2.boundingRect(cnt)
dst = img[y:y+h, x:x+w]
cv2.imwrite("001.png", dst)

结果：

Answer 2

Kinght的solution效果很好。就我而言，我也有CMYK图像。当我裁剪它们时，我得到不正确（鲜艳的颜色）输出。似乎OpenCV不支持CMYK。所以我需要一种方法将CMYK图像转换为RGB，然后用OpenCV打开它。这是我处理它的方式：

import cv2
import numpy

from PIL import Image
from PIL import ImageCms

# force opening truncated/corrupt image files
from PIL import ImageFile
ImageFile.LOAD_TRUNCATED_IMAGES = True

img = "shoes.jpg"

img = Image.open(img)
if img.mode == "CMYK":
    # color profiles can be found at C:\Program Files (x86)\Common Files\Adobe\Color\Profiles\Recommended
    img = ImageCms.profileToProfile(img, "USWebCoatedSWOP.icc", "sRGB_Color_Space_Profile.icm", outputMode="RGB")
# PIL image -> OpenCV image; see https://stackoverflow.com/q/14134892/2202732
img = cv2.cvtColor(numpy.array(img), cv2.COLOR_RGB2BGR)

## (1) Convert to gray, and threshold
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
th, threshed = cv2.threshold(gray, 240, 255, cv2.THRESH_BINARY_INV)

## (2) Morph-op to remove noise
kernel = cv2.getStructuringElement(cv2.MORPH_ELLIPSE, (11,11))
morphed = cv2.morphologyEx(threshed, cv2.MORPH_CLOSE, kernel)

## (3) Find the max-area contour
cnts = cv2.findContours(morphed, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[-2]
cnt = sorted(cnts, key=cv2.contourArea)[-1]

## (4) Crop and save it
x,y,w,h = cv2.boundingRect(cnt)
dst = img[y:y+h, x:x+w]

# add border/padding around the cropped image
# dst = cv2.copyMakeBorder(dst, 10, 10, 10, 10, cv2.BORDER_CONSTANT, value=[255,255,255])

cv2.imshow("image", dst)
cv2.waitKey(0)
cv2.destroyAllWindows()

# create/write to file
# cv2.imwrite("001.png", dst)

Answer 3

This链接对我来说非常适合类似的问题，尽管它使用PIL。请注意，它会产生一个矩形图像，由顶部/右侧/底部/最左侧的非白色像素限定。在您的情况下，它应该提供相同大小的相同图像。

我猜测代码可以很容易地适应OpenCV函数。