plt.imshow() 在另一个图像中显示图像

Question

我是 Python 的新手，如果这是非常基础的内容，我深表歉意。我正在做图像处理，但是当我使用 cv2 读取 png 图像然后使用 plt.imshow() 显示图像时，它给了我奇怪的图像（带有额外边界的图像）。我做了以下。

import cv2
import numpy as np

img1 = cv2.imread('img.png',cv2.IMREAD_GRAYSCALE)
plt.figure(figsize=(10,4))
plt.imshow(img1, 'gray')
plt.title("ORIGINAL")
plt.savefig("original.png")

  
kernel = np.ones((4,4),np.uint8)
opening = cv2.morphologyEx(img1, cv2.MORPH_OPEN, kernel)
plt.figure(figsize=(10,4))
plt.imshow(opening, 'gray')
plt.title("OPENING OF ORIGINAL")
plt.savefig("opening of original.png")

我在这里附上生成的图像。

[原图]

[通过plt.imshow()显示图像后。]

[做开图处理技术后]

Answer 1

你说的多余部分是红色区域吗？

如果我没理解错的话，这段代码可以用来切掉图片的透明部分

import cv2
import numpy as np
import matplotlib.pyplot as plt

def cv2_crop(im, box):
    return im.copy()[box[1]:box[3], box[0]:box[2], :]

def get_transparency_location(image):
    height, width, channel = image.shape  
    assert channel == 4  
    first_location = None  
    last_location = None  
    first_transparency = []  
    last_transparency = []  
    for y, rows in enumerate(image):
        for x, BGRA in enumerate(rows):
            alpha = BGRA[3]
            if alpha != 0:
                if not first_location or first_location[1] != y:  
                    first_location = (x, y)  
                    first_transparency.append(first_location)
                last_location = (x, y)  
        if last_location:
            last_transparency.append(last_location)

    top = first_transparency[0]
    bottom = first_transparency[-1]
    left = None
    right = None
    for first, last in zip(first_transparency, last_transparency):
        if not left:
            left = first
        if not right:
            right = last
        if first[0] < left[0]:
            left = first
        if last[0] > right[0]:
            right = last

    upper_left = (left[0], top[1])  
    bottom_right = (right[0], bottom[1])  
    box =upper_left[0], upper_left[1], bottom_right[0], bottom_right[1]
    result = cv2_crop(image, box)
    #cv2.imwrite('result.png', result)
    return result
    


if __name__ == '__main__':
    #img1 = cv2.imread('img.png',cv2.IMREAD_GRAYSCALE)
    image = cv2.imread('img.png', cv2.IMREAD_UNCHANGED)  
    img1 = get_transparency_location(image)

    plt.figure(figsize=(10,4))
    plt.imshow(img1, 'gray')
    plt.title("ORIGINAL")
    plt.savefig("original.png")


    kernel = np.ones((4,4),np.uint8)
    opening = cv2.morphologyEx(img1, cv2.MORPH_OPEN, kernel)
    plt.figure(figsize=(10,4))
    plt.imshow(opening, 'gray')
    plt.title("OPENING OF ORIGINAL")
    plt.savefig("opening of original.png")

Answer 2

以下是如何按原样保存图像，不添加任何边框或填充：

import cv2
import numpy as np
import matplotlib.pyplot as plt

img1 = cv2.imread('matches.png', cv2.IMREAD_GRAYSCALE) 
kernel = np.ones((4, 4), np.uint8)
opening = cv2.morphologyEx(img1, cv2.MORPH_OPEN, kernel)
fig = plt.figure(frameon=False)
fig.set_size_inches(10, 4)
ax = plt.Axes(fig, [0., 0., 1., 1.])
ax.set_axis_off()
fig.add_axes(ax)

ax.imshow(img1, cmap='gray', aspect='auto')
fig.savefig("original.png")

ax.imshow(opening, cmap='gray', aspect='auto')
fig.savefig("opening of original.png")

输入图像：

输出图像：

当然，如果你不需要使用matplotlib你可以简单地使用cv2.imwrite() to write the images (and cv2.show()来显示图像):

import cv2
import numpy as np

img1 = cv2.imread('matches.png', cv2.IMREAD_GRAYSCALE) 
kernel = np.ones((4,4),np.uint8)
opening = cv2.morphologyEx(img1, cv2.MORPH_OPEN, kernel)

cv2.imwrite("original.png", img1)
cv2.imwrite("opening of original.png", opening)

plt.imshow() 在另一个图像中显示图像

plt.imshow() display the image inside another image

python

opencv

image-processing

matplotlib