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python - PIL : Generating Vertical Gradient Image

转载 作者:太空宇宙 更新时间:2023-11-04 08:05:08 25 4
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在 Android 中,我使用以下代码生成我需要的渐变背景:

<gradient
android:angle="90"
android:startColor="#40000000"
android:endColor="#00000000"
android:type="linear" />

背景从上到下从亮到相对暗。我想知道如何使用 PIL 在 Python 中执行相同的操作,因为我需要在另一个用 Python 编写的程序上实现相同的效果。

最佳答案

这里展示了绘制多色矩形水平和垂直渐变的方法。

rom PIL import Image, ImageDraw

BLACK, DARKGRAY, GRAY = ((0,0,0), (63,63,63), (127,127,127))
LIGHTGRAY, WHITE = ((191,191,191), (255,255,255))
BLUE, GREEN, RED = ((0, 0, 255), (0, 255, 0), (255, 0, 0))


class Point(object):
def __init__(self, x, y):
self.x, self.y = x, y

class Rect(object):
def __init__(self, x1, y1, x2, y2):
minx, maxx = (x1,x2) if x1 < x2 else (x2,x1)
miny, maxy = (y1,y2) if y1 < y2 else (y2,y1)
self.min = Point(minx, miny)
self.max = Point(maxx, maxy)

width = property(lambda self: self.max.x - self.min.x)
height = property(lambda self: self.max.y - self.min.y)


def gradient_color(minval, maxval, val, color_palette):
""" Computes intermediate RGB color of a value in the range of minval
to maxval (inclusive) based on a color_palette representing the range.
"""
max_index = len(color_palette)-1
delta = maxval - minval
if delta == 0:
delta = 1
v = float(val-minval) / delta * max_index
i1, i2 = int(v), min(int(v)+1, max_index)
(r1, g1, b1), (r2, g2, b2) = color_palette[i1], color_palette[i2]
f = v - i1
return int(r1 + f*(r2-r1)), int(g1 + f*(g2-g1)), int(b1 + f*(b2-b1))

def horz_gradient(draw, rect, color_func, color_palette):
minval, maxval = 1, len(color_palette)
delta = maxval - minval
width = float(rect.width) # Cache.
for x in range(rect.min.x, rect.max.x+1):
f = (x - rect.min.x) / width
val = minval + f * delta
color = color_func(minval, maxval, val, color_palette)
draw.line([(x, rect.min.y), (x, rect.max.y)], fill=color)

def vert_gradient(draw, rect, color_func, color_palette):
minval, maxval = 1, len(color_palette)
delta = maxval - minval
height = float(rect.height) # Cache.
for y in range(rect.min.y, rect.max.y+1):
f = (y - rect.min.y) / height
val = minval + f * delta
color = color_func(minval, maxval, val, color_palette)
draw.line([(rect.min.x, y), (rect.max.x, y)], fill=color)


if __name__ == '__main__':
# Draw a three color vertical gradient.
color_palette = [BLUE, GREEN, RED]
region = Rect(0, 0, 730, 350)
width, height = region.max.x+1, region.max.y+1
image = Image.new("RGB", (width, height), WHITE)
draw = ImageDraw.Draw(image)
vert_gradient(draw, region, gradient_color, color_palette)
image.show()
#image.save("vert_gradient.png", "PNG")
#print('image saved')

这是它生成并显示的图像:

screenshot of gradient image created

这会计算 RGB color space 中的中间颜色, 但可以使用其他颜色空间——例如比较我对问题 Range values to pseudocolor 的回答结果.

这可以轻松扩展以生成 RGBA (RGB+Alpha) 模式图像。

关于python - PIL : Generating Vertical Gradient Image,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32530345/

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