如何用python创建透明的径向渐变？

Question

我正在尝试创建一个渐变到清晰背景的径向渐变。我的目标是创建这个渐变并将其作为背景粘贴到另一个图像。

So far, i have been able to create a circular gradient, but it i not transparent. i found the code below in stackoverflow :

imgsize=(650,650)
image = Image.new('RGBA', imgsize)
innerColor = [153,0,0]
for y in range(imgsize[1]):
    for x in range(imgsize[0]):
         distanceToCenter = math.sqrt((x - imgsize[0]/2) ** 2 + (y - imgsize[1]/2) ** 2)
         distanceToCenter = float(distanceToCenter) / (math.sqrt(2) * imgsize[0]/2)
         r = distanceToCenter + innerColor[0] * (1 - distanceToCenter)
         g =  distanceToCenter + innerColor[1] * (1 - distanceToCenter)
         b =  distanceToCenter + innerColor[2] * (1 - distanceToCenter)
         image.putpixel((x, y), (int(r), int(g), int(b)))

this is the image that is produced i would like to not have it fade to black, but to clear instead.

thank you for your help :)

Answer 1

我想我只需绘制纯红色并使用Numpy计算透明层并将其推入：

#!/usr/bin/env python3

import numpy as np
from PIL import Image

# Define width and height of image
W, H = 650, 650

# Create solid red image
im = Image.new(mode='RGB', size=(W,H), color=(153,0,0))

# Create radial alpha/transparency layer. 255 in centre, 0 at edge
Y = np.linspace(-1, 1, H)[None, :]*255
X = np.linspace(-1, 1, W)[:, None]*255
alpha = np.sqrt(X**2 + Y**2)
alpha = 255 - np.clip(0,255,alpha)

# Push that radial gradient transparency onto red image and save
im.putalpha(Image.fromarray(alpha.astype(np.uint8)))
im.save('result.png')

关键词：Python、图像处理、径向渐变、alpha、透明度。