Question

基本上，我正在尝试制作一个将采用给定图像和颜色的函数。对于图像中的每个像素，它将保留原始的alpha值，但是会将颜色更改为给定的颜色。

例如，如果函数获得下面的箭头图像和红色，

它将输出以下图像：

在Photoshop和其他图像编辑器中，此效果称为“颜色叠加”。在PIL中是否有任何快速简便的方法来达到相同的结果？提前致谢！（;

Answer 1

一种方法是创建一个与原始图像大小相同的红色实心图像，然后将原始图像的alpha通道复制到该图像上：

from PIL import Image

# Open original image and extract the alpha channel
im = Image.open('arrow.png')
alpha = im.getchannel('A')

# Create red image the same size and copy alpha channel across
red = Image.new('RGBA', im.size, color='red')
red.putalpha(alpha)

这是使用Numpy的第二种方法：

from PIL import Image
import numpy as np

# Open image
im = Image.open('arrow.png')

# Make into Numpy array
n = np.array(im) 

# Set first three channels to red
n[...,0:3]=[255,0,0] 

# Convert back to PIL Image and save
Image.fromarray(n).save('result.png')

第三种方法是使用相似大小的红色副本进行合成，并使用原始的alpha蒙版：

from PIL import Image

# Open image
im = Image.open('arrow.png')                                                                                                       

# Make solid red image same size
red = Image.new('RGBA', im.size, color='red')                                                                                      

# Composite the two together, honouring the original mask
im = Image.composite(red,im,im)

关键字：图像，图像处理，Python，Pillow，PIL，Numpy，提取alpha，alpha通道，透明度，替换透明度，复制透明度，复制alpha，移植alpha，移植透明度。 >

Answer 2

让我们考虑以下图片-http://www.libpng.org/pub/png/img_png/globe-scene-fish-bowl-pngcrush.png

image = cv2.imread("/home/thalish/bleed_test/globe-scene-fish-bowl-pngcrush.png",cv2.IMREAD_UNCHANGED)

image[:,:,0],image[:,:,1],image[:,:,2] = (255,0,0) #to replace all pixels with Red but keep alpha channel unchanged

Answer 3

尝试：

from PIL import Image

# Takes the input image
img = Image.open(r"Arrow.png")

# Getting the dimensions of the image
x, y = img.size

# Obtaining values of Red, Green, Blue for each opaque pixel
red = int(input("Enter the red value you want in each pixel = "))
green = int(input("Enter the green value you want in each pixel = "))
blue = int(input("Enter the blue value you want in each pixel = "))

i = j = 0

# This loop makes sure that alpha only has two discrete values (0 , 255)
# This is to ensure that constant color is obtained, at pixels where transparence may not be 255
# (prevents color escapes at pixels where total transparency is not achieved)
while i < x:
    while j < y:
        r, g, b, a = img.getpixel((i,j))
        if a > 200 and a < 256:
            a = 255
        else:
            a = 0
        img.putpixel((i,j),(r,g,b,a))
        j += 1
    j = 0
    i += 1

i = j = 0

# Two nested loops
# Outer one goes through rows of image
# Inner one (nested one) goes through columns of image
while i < x:
    while j < y:

        # This condition checks, if the value of alpha for that individual pixel is 255 (~opaque), 
        # if true then change its RGB values to user defined values
        if img.getpixel((i,j))[-1] == 255:
            img.putpixel((i,j), (red, green, blue, 255))
        j += 1
    j = 0
    i += 1

img.save("Arrow.png")

输入：-

Enter the red value you want in each pixel = 0
Enter the green value you want in each pixel = 0
Enter the blue value you want in each pixel = 255

输出：-

第一圈的勘探：-

如果第一个循环没有结束，alpha的值将达到阈值，则在输出图像中会产生很多错误。也就是说，靠近对象边缘的像素值倾向于使alpha像素值比255（总不透明度）小一点，以实现平滑的抗锯齿。如果这些像素被丢弃，则输出图像可能看起来像这样：-

PS：-尽管OpenCV是大多数图像分析师/专家的首选，但我绝对建议您在开始时坚持使用PIL / Pillow，因为它可以让您获得以一种非常友好的方式掌握成像的基础知识。不可否认，OpenCV在几乎所有方面都远远超过了PIL，但是，即使您一开始就学习PIL，从PIL过渡到OpenCV也会为您以后的工作提供很多便利。

用颜色填充图像，但保留Alpha（PIL中的颜色叠加）

3 个答案: