如何改变渐变的颜色方向

Question

下面产生一个从左边开始的渐变。

#!/usr/bin/env python
import math
from PIL import Image
im = Image.new('RGB', (300, 300))
ld = im.load()
# A map of rgb points in your distribution
# [distance, (r, g, b)]
# distance is percentage from left edge
heatmap = [
    [0.0, (0, 0, 0)],
    [1.00, (0.8, 0.0, 1.0)],
]

def gaussian(x, a, b, c, d=0):
    return a * math.exp(-(x - b) ** 2 / (2 * c ** 2)) + d

def pixel(x, width=100, map=[], spread=1):
    width = float(width)
    r = sum([gaussian(x, p[1][0], p[0] * width, width / (spread * len(map))) for p in map])
    g = sum([gaussian(x, p[1][1], p[0] * width, width / (spread * len(map))) for p in map])
    b = sum([gaussian(x, p[1][2], p[0] * width, width / (spread * len(map))) for p in map])
    return min(1.0, r), min(1.0, g), min(1.0, b)

for x in range(im.size[0]):
    r, g, b = pixel(x, width=300, map=heatmap)
    r, g, b = [int(256 * v) for v in (r, g, b)]
    for y in range(im.size[1]):
        ld[x, y] = r, g, b
im.show()

我如何改变梯度的起始位置，上面是从左到右，但是如果我想从上到下呢?

Answer 1

只需反转像素分配中的坐标:

    ld[x, y] = r, g, b

是

    ld[y, x] = r, g, b