PIL:生成垂直渐变图像 [英] PIL: Generating Vertical Gradient Image

问题描述

在Android中，我使用以下代码生成了我需要的渐变背景:

In Android, I used the following code to generate a gradient background that I need:

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

背景从上到下从浅变暗.我想知道如何在带有PIL的Python中执行相同的操作，因为我需要对另一个用Python编写的程序具有相同的效果.

The background goes from light to relatively dark from top to bottom. I wonder how to do the same in Python with PIL, since I need the same effect on another program written in Python.

推荐答案

以下内容显示了绘制多色矩形水平和垂直渐变的方法.

Here's something that shows ways to draw either multicolor rectangular horizontal and vertical gradients.

from 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

    @staticmethod
    def from_point(other):
        return Point(other.x, other.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)

    @staticmethod
    def from_points(p1, p2):
        return Rect(p1.x, p1.y, p2.x, p2.y)

    def __str__(self):
        return 'Rect({:d}, {:d}, {:d}, {:d})'.format(self.min.x, self.min.y,
                                                     self.max.x, self.max.x)
    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
    v = float(val-minval) / float(maxval-minval) * 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
    for x in range(rect.min.x, rect.max.x+1):
        f = (x - rect.min.x) / float(rect.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
    for y in range(rect.min.y, rect.max.y+1):
        f = (y - rect.min.y) / float(rect.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)

color_palette = [BLUE, GREEN, RED]
region = Rect(0, 0, 730, 350)
imgx, imgy = region.max.x+1, region.max.y+1
image = Image.new("RGB", (imgx, imgy), 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:

And here's the image it generates and displays:

这会插值RGB色彩空间中的中间色彩，但可以使用其他色彩空间-例如，请参见我对问题

This interpolates the in-between colors in the RGB-colorspace, but other colorspaces could be used — for examples see my answers to the question Range values to pseudocolor.

可以很容易地扩展为生成ARGB(Alpha + RGB)图像.

This could easily be extended to generate ARGB (Alpha+RGB) images.

这篇关于PIL:生成垂直渐变图像的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！