python - 使用 PIL 或 Scipy 将 Python 图像从 RGB 转换为单 channel

Question

是否有一种已知的解决方案可以使用 PIL(或 Scipy)将图像从具有 3 个 channel (RGB)转换为只有一个 channel

我尝试将图像转换为 Grayscale 并按照下面的代码保存为 png，图像仍然有 3 个颜色 channel 。

from glob import glob
import os
import os.path
from PIL import Image

SIZE = 32, 32

# set directory
# os.chdir('..data/unprocessed_cats')

# filter all jpg and png images
IMAGE_FILES = glob('../data/validation/cats/*.jpg')

IMAGE_COUNTER = 1
print IMAGE_FILES
# iterate over files
for image_file in IMAGE_FILES:

    # open file and resize
    try:
        im = Image.open(image_file)
    except:
        pass
    im = im.resize(SIZE, Image.ANTIALIAS)

    # save locally
    output_filename = "%s.png" % IMAGE_COUNTER
    # Grayscale
    im.convert('LA').save(os.path.join('../data/validation', 'cats_processed', output_filename), "PNG")


    # incriment image counter
    IMAGE_COUNTER = IMAGE_COUNTER + 1

Answer 1

我尝试只使用 im.convert('L') 但它用黑色替换了透明度(将我的整个图像变成黑色)。

我从 Remove transparency/alpha from any image using PIL 中找到了以下代码非常有帮助(汉弗莱的全部学分):

def remove_transparency(im, bg_colour=(255, 255, 255)):

    # Only process if image has transparency 
    if im.mode in ('RGBA', 'LA') or (im.mode == 'P' and 'transparency' in im.info):

        # Need to convert to RGBA if LA format due to a bug in PIL 
        alpha = im.convert('RGBA').split()[-1]

        # Create a new background image of our matt color.
        # Must be RGBA because paste requires both images have the same format

        bg = Image.new("RGBA", im.size, bg_colour + (255,))
        bg.paste(im, mask=alpha)
        return bg

    else:
        return im

先去除透明度，然后用 im.convert('L') 转换它返回灰度模式:

im = remove_transparency(im).convert('L')