我如何使我的Numpy圖像在python中采用Alpha通道值

Question

我試圖使圖像的背景透明。 我已經將所有想要透明的部分切成黑色。 但是python給我一條關於僅服用RBG的錯誤消息。 我收到的錯誤消息是“無法將大小為4的序列復制到維度為3的數組軸上”那么如何使python識別alpha通道並允許我對其進行操作？

import matplotlib.pyplot as plt 
import os.path
import numpy as np 
import PIL




def mask(row, column) :
    for row in range(0, 383) :
        for column in range(0, 86) :
            img[row][column] = [0, 0, 0]
    for row in range(230, 383) :
        for column in range(0, 286) :
            img[row][column] = [0, 0, 0]
    for row in range(0, 50) :
        for column in range(0, 286) :
            img[row][column] = [0, 0, 0]
    for row in range(0, 383) :
        for column in range(199, 286) :
            img[row][column] = [0, 0, 0]




directory = os.path.dirname(os.path.abspath(__file__)) 

filename = os.path.join(directory, 'PicOfNick.jpg')

img = plt.imread(filename)

fig, ax = plt.subplots(1, 1)

mask(283, 287) 
np_img = np.array(img)
width = len(img[0])
height = len(img)
for h in range(48, 230) :
    for w in range(84, 200) :
        if np_img[h][w][0] in range(50, 90) :
            np_img[h][w] = (0, 0, 0)
        if sum(np_img[h][w]) == 0 :
            np_img[h][w] = (0, 0, 0)



ax.imshow(np_img, interpolation='none')

fig.show()

Answer 1

您確實應該嘗試避免使用Numpy / Python遍歷圖像，因為它速度慢且容易出錯。 這是使所有黑色像素透明的方法。

從此圖像開始：

#!/usr/bin/env python3

from PIL import Image
import numpy as np


# Load image and ensure it is 3-channel RGB...
# ... not 1-channel greyscale, not 4-channel RGBA, not 1-channel palette
im = Image.open('start.png').convert('RGB')

# Make into Numpy array of RGB and get dimensions
RGB = np.array(im)
h, w = RGB.shape[:2]

# Add an alpha channel, fully opaque (255)
RGBA = np.dstack((RGB, np.zeros((h,w),dtype=np.uint8)+255))

# Make mask of black pixels - mask is True where image is black
mBlack = (RGBA[:, :, 0:3] == [0,0,0]).all(2)

# Make all pixels matched by mask into transparent ones
RGBA[mBlack] = (0,0,0,0)

# Convert Numnpy array back to PIL Image and save
Image.fromarray(RGBA).save('result.png')