python - 为什么我收到 ValueError : too many values to unpack (expected 3)?

Question

我找到了这个 RGB 图像分析并尝试在一些随机图片上使用它。

http://marksolters.com/programming/2015/02/27/rgb-histograph.html

import numpy as np
import mpl_toolkits.mplot3d.axes3d as p3
import matplotlib.pyplot as plt
import colorsys
from PIL import Image

# (1) Import the file to be analyzed!
img_file = Image.open("another_photo.jpeg")
img = img_file.load()

# (2) Get image width & height in pixels
[xs, ys] = img_file.size
max_intensity = 100
hues = {}

# (3) Examine each pixel in the image file
for x in range(0, xs):
  for y in range(0, ys):
    # (4)  Get the RGB color of the pixel
    [r, g, b] = img[x, y]
    # (5)  Normalize pixel color values
    r /= 255.0
    g /= 255.0
    b /= 255.0

    # (6)  Convert RGB color to HSV
    [h, s, v] = colorsys.rgb_to_hsv(r, g, b)

    # (7)  Marginalize s; count how many pixels have matching (h, v)
    if h not in hues:
      hues[h] = {}
    if v not in hues[h]:
      hues[h][v] = 1
    else:
      if hues[h][v] < max_intensity:
        hues[h][v] += 1

# (8)   Decompose the hues object into a set of one dimensional arrays we can use with matplotlib
h_ = []
v_ = []
i = []
colours = []

for h in hues:
  for v in hues[h]:
    h_.append(h)
    v_.append(v)
    i.append(hues[h][v])
    [r, g, b] = colorsys.hsv_to_rgb(h, 1, v)
    colours.append([r, g, b])

# (9)   Plot the graph!
fig = plt.figure()
ax = p3.Axes3D(fig)
ax.scatter(h_, v_, i, s=5, c=colours, lw=0)

ax.set_xlabel('Hue')
ax.set_ylabel('Value')
ax.set_zlabel('Intensity')
fig.add_axes(ax)
plt.show()

但是我的代码在第 20 行中断:

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

有人可以向我解释一下作者如何以及为什么从 img 中解压这两个值并将它们分配给三个变量吗？

Answer 1

这取决于图像。你的可能是 RGBA，然后像素元组有 4 个值，最后一个是 ALPHA。您可以使用 .convert('RGB') 如下:

im = Image.open(file_name).convert('RGB')
width, height = im.size
pixels = im.load()

# this list comprehension will get you the list of all pixels in RGB format
all_pixels = [pixels[x,y] for y in range(height) for x in range(width)]