python - 将 PIL 图像转换为 numpy 数组有时不起作用

Question

我有这段代码来打开图像并将其转换为灰度:

with Image.open(file_path).convert(mode='L') as image:
    ...
    block = image.crop((start_x, start_y, end_x, end_y))
    art[row] += tslt_block(block)

其中 tslt_block() 定义如下:

def tslt_block(img):
    char_table = "$@B%8&WM#*oahkbdpqwmZO0QLCJUYXzcvunxrjft/\|()1{}[]?-_+~<>i!lI;:,\"^`'. "
 -> a = np.array(img)
    gray_scale = a.mean()
    return char_table[int(gray_scale / 255 * (len(char_table) - 1))]

问题是，箭头标记的行(a = np.array(img))似乎没有效果!此行执行后，a 与 img 是同一个对象:

这很奇怪，因为此代码应该将图像转换为 numpy 数组，如以下控制台 session 所示:

我无法理解这个!为什么同一行代码有时有效有时无效？

更新:似乎转换整个图像有效，但转换裁剪却无效:

我的完整代码是:

from PIL import Image
import numpy as np
import math, os

scale = 0.43


def tslt_block(img):
    char_table = "$@B%8&WM#*oahkbdpqwmZO0QLCJUYXzcvunxrjft/\|()1{}[]?-_+~<>i!lI;:,\"^`'. "
    a = np.array(img)
    gray_scale = a.mean()
    return char_table[int(gray_scale / 255 * (len(char_table) - 1))]


def main():
    file_path = input('input full file path: ')
    base_name, *_ = os.path.splitext(file_path)
    output_file_path = base_name + '.txt'
    columns = int(input('input number of columns: '))

    with Image.open(file_path).convert(mode='L') as image:
        width, height = image.size
        block_width = width / columns
        block_height = block_width / scale
        rows = math.ceil(height / block_height)
        art = []
        for row in range(rows):
            art.append('')
            for column in range(columns):
                start_x, start_y = column * block_width, row * block_height
                end_x = int(start_x + block_width if start_x + block_width < width else width)
                end_y = int(start_y + block_height if start_y + block_height < height else height)
                block = image.crop((start_x, start_y, end_x, end_y))
                art[row] += tslt_block(block)

    with open(output_file_path, 'w') as output_file:
        output_file.write('\n'.join(art))
        print('output written to {}'.format(output_file_path))


if __name__ == '__main__':
    main()

我用于测试的图像是:

Answer 1

好的，我已经解决了我自己的问题。似乎如果 start_x 和 start_y 是浮点型，那么将裁剪后的图像更改为 numpy 数组将不起作用。如果我将它们转换为 int，它就可以工作。但我还是想知道为什么。 Pillow 或 numpy 是否存在错误？