Question

我正在尝试浏览我用Raspberry pi相机拍摄的png的每个像素，并有选择地更改高于或低于某个r，g或b值的像素。我知道这是一个非常低效的算法，我只是试图了解python脚本。我从代码中找到了来自@ Constantin代码的代码：How can I read the RGB value of a given pixel in Python? 他的代码如下。

import png, array

point = (2, 10) # coordinates of pixel to be painted red

reader = png.Reader(filename='image.png')
w, h, pixels, metadata = reader.read_flat()
pixel_byte_width = 4 if metadata['alpha'] else 3
#The line below is, I think wrong. I'll point out the what I did in my code below
pixel_position = point[0] + point[1] * w 
new_pixel_value = (255, 0, 0, 0) if metadata['alpha'] else (255, 0, 0)
pixels[
  pixel_position * pixel_byte_width :
  (pixel_position + 1) * pixel_byte_width] = array.array('B', new_pixel_value)

output = open('image-with-red-dot.png', 'wb')
writer = png.Writer(w, h, **metadata)
writer.write_array(output, pixels)
output.close()

我改为：

#!/usr/bin/python

import png, array

reader = png.Reader(filename='test.png')
w, h, pixels, metadata = reader.read_flat()
pixel_byte_width = 4 if metadata['alpha'] else 3

for x in range(w):
    for y in range(h):
        point_index = x+(y-1)*w#This is the bit that I said I'd fix above.
        r = pixels[point_index * pixel_byte_width + 0]
        g = pixels[point_index * pixel_byte_width + 1]
        b = pixels[point_index * pixel_byte_width + 2]
        pixel = pixels[point_index * pixel_byte_width : 
            (point_index+1) * pixel_byte_width]
        #Above we have all the info about each byte, and below is our devious plan
        new_pixel = (0, 0, 0, 0) if metadata['alpha'] else (0, 0, 0)
        #if g > 175:
        pixel = array.array('B', new_pixel)

output = open('test_edited.png', 'wb')
writer = png.Writer(w, h, **metadata)
writer.write_array(output, pixels)
output.close()

pi会想一两分钟，然后我就可以打开一个完全相同的新png。我的脚本缺少什么，或者是否有一个比python更好的平台在Raspbian Jessie上按像素进行操作？

非常感谢！

Answer 1

如果您对新库开放，我建议pillow，Python成像库（PIL）的后续版本。它更简单，不仅限于png。 Documentation is here.

from PIL import Image, ImageDraw

img = Image.open('image.png')
img = img.convert("RGB") # Make sure we are in 8-bit RGB
draw = ImageDraw.Draw(img)

for y in range(img.height):
    for x in range(img.width):
        # getpixel returns a tuple with (R, G, B)
        if img.getpixel((x, y))[1] > 175: # If too green
            draw.point((x,y), '#000000') # Color syntax is CSS-like

img.save('test_edited.png', 'PNG')
# You can also use img.show() in a graphical environment

在Raspbian上用PyPNG选择性地改变png像素

1 个答案: