使用PIL使所有白色像素透明?

您需要进行以下更改:

• (255, 255, 255, 0) 而不是列表 [255, 255, 255, 0]
• 使用 img.putdata(newData)

这是工作代码:

from PIL import Image

img = Image.open('img.png')
img = img.convert("RGBA")
datas = img.getdata()

newData = []
for item in datas:
    if item[0] == 255 and item[1] == 255 and item[2] == 255:
        newData.append((255, 255, 255, 0))
    else:
        newData.append(item)

img.putdata(newData)
img.save("img2.png", "PNG")

您还可以使用像素访问模式就地修改图像:

from PIL import Image

img = Image.open('img.png')
img = img.convert("RGBA")

pixdata = img.load()

width, height = img.size
for y in range(height):
    for x in range(width):
        if pixdata[x, y] == (255, 255, 255, 255):
            pixdata[x, y] = (255, 255, 255, 0)

img.save("img2.png", "PNG")

如果你经常使用,你也可以把上面的内容包装成一个脚本。

import numpy as np

def white_to_transparency(img):
    x = np.asarray(img.convert('RGBA')).copy()

    x[:, :, 3] = (255 * (x[:, :, :3] != 255).any(axis=2)).astype(np.uint8)

    return Image.fromarray(x)

def white_to_transparency_gradient(img):
    x = np.asarray(img.convert('RGBA')).copy()

    x[:, :, 3] = (255 - x[:, :, :3].mean(axis=2)).astype(np.uint8)

    return Image.fromarray(x)

备注: .copy()

import Image
import ImageMath

def distance2(a, b):
    return (a[0] - b[0]) * (a[0] - b[0]) + (a[1] - b[1]) * (a[1] - b[1]) + (a[2] - b[2]) * (a[2] - b[2])

def makeColorTransparent(image, color, thresh2=0):
    image = image.convert("RGBA")
    red, green, blue, alpha = image.split()
    image.putalpha(ImageMath.eval("""convert(((((t - d(c, (r, g, b))) >> 31) + 1) ^ 1) * a, 'L')""",
        t=thresh2, d=distance2, c=color, r=red, g=green, b=blue, a=alpha))
    return image

if __name__ == '__main__':
    import sys
    makeColorTransparent(Image.open(sys.argv[1]), (255, 255, 255)).save(sys.argv[2]);

一种更Python化的方式,因为循环一个大图像需要很长时间

from PIL import Image

img = Image.open('img.png')
img = img.convert("RGBA")

imgnp = np.array(img)

white = np.sum(imgnp[:,:,:3], axis=2)
white_mask = np.where(white == 255*3, 1, 0)

alpha = np.where(white_mask, 0, imgnp[:,:,-1])

imgnp[:,:,-1] = alpha 

img = Image.fromarray(np.uint8(imgnp))
img.save("img2.png", "PNG")

此函数结合了前面解决方案的所有优点:它允许任何背景并使用numpy(比经典列表更快)。

import numpy as np
from PIL import Image

def convert_png_transparent(src_file, dst_file, bg_color=(255,255,255)):
    image = Image.open(src_file).convert("RGBA")
    array = np.array(image, dtype=np.ubyte)
    mask = (array[:,:,:3] == bg_color).all(axis=2)
    alpha = np.where(mask, 0, 255)
    array[:,:,-1] = alpha
    Image.fromarray(np.ubyte(array)).save(dst_file, "PNG")

Python 3版本,所有文件都在一个目录中

import glob
from PIL import Image

def transparent(myimage):
    img = Image.open(myimage)
    img = img.convert("RGBA")

    pixdata = img.load()

    width, height = img.size
    for y in range(height):
        for x in range(width):
            if pixdata[x, y] == (255, 255, 255, 255):
                pixdata[x, y] = (255, 255, 255, 0)

    img.save(myimage, "PNG")

for image in glob.glob("*.png"):
    transparent(image)

https://stackoverflow.com/a/62334218/5189462

from PIL import Image

target_color = (255, 255, 255)

img   = Image.open('img.png')
imga  = img.convert("RGBA")
datas = imga.getdata()

newData = list()
for item in datas:
    newData.append((
        item[0], item[1], item[2],
        max( 
            abs(item[0] - target_color[0]), 
            abs(item[1] - target_color[1]), 
            abs(item[2] - target_color[2]), 
        )  
    ))

imgb = Image.frombuffer("RGBA", imga.size, newData, "raw", "RGBA", 0, 1)
imgb.save("img2.png", "PNG")