Python:使用PIL加载png文件会产生奇怪的结果 [英] Python: Use PIL to load png file gives strange results
本文介绍了Python:使用PIL加载png文件会产生奇怪的结果的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我从VOC2012数据集中获取了以下png文件.
I took the following png file from VOC2012 dataset.
我使用了以下简单代码:
I used the following simple code:
import numpy as np
from PIL import Image
import matplotlib.pyplot as plt
%matplotlib inline
img = Image.open(filename) # filename is the png file in question
img.show()
arr = np.array(img)
plt.imshow(arr, cmap='gray')
它产生了以下图像:
这很奇怪，因为结果不是原始图像的灰度图像. 上面的代码还用于deeplab tensorflow数据集中，以消除真实图像中的颜色图.
It is strange since the result is not the gray-scaled image of the original one. The above code is also used in deeplab tensorflow dataset to remove the colormap in the ground-truth images.
有人知道为什么吗?非常感谢！
Anyone knows why? Many thanks!
推荐答案
问题是您的图像已调色板化.因此，没有为每个像素存储完整的RGB三元组，而是有一个256个RGB三元组的列表，然后在每个像素位置，它只是将索引存储到列表中-这样可以节省空间.
The problem is that your image is palettised. So, rather than storing a full RGB triplet for each pixel, there is a list of 256 RGB triplets and then at each pixel location it just stores the index into the list - which saves space.
我认为您需要这个:
#!/usr/local/bin/python3
import numpy as np
from PIL import Image
import matplotlib.pyplot as plt
#%matplotlib inline
img = Image.open('cycle.png').convert('RGB').convert('L')
img.show()
arr = np.array(img)
plt.imshow(arr, cmap='gray')
响应您在评论中的进一步问题，是的，选项板条目255表示E0E0C0.我在终端中使用以下命令，使用 ImageMagick 进行了显示，以显示图像详细信息并转储调色板.请参见下面的列表行:
In response to your further question in the comments, yes, the palette entry 255 represents E0E0C0. I checked using ImageMagick to show image details and dump the palette, using the following command in the Terminal. See the list line below:
identify -verbose cycle.png
Image: cycle.png
Format: PNG (Portable Network Graphics)
Mime type: image/png
Class: PseudoClass
Geometry: 334x500+0+0
Units: Undefined
Colorspace: sRGB
Type: Palette
Base type: Undefined
Endianess: Undefined
Depth: 8-bit
Channel depth:
Red: 8-bit
Green: 8-bit
Blue: 8-bit
Channel statistics:
Pixels: 167000
Red:
min: 0 (0)
max: 224 (0.878431)
mean: 93.4808 (0.366591)
standard deviation: 99.7578 (0.391207)
kurtosis: -1.93947
skewness: 0.148046
entropy: 0.854702
Green:
min: 0 (0)
max: 224 (0.878431)
mean: 96.2489 (0.377447)
standard deviation: 72.6758 (0.285003)
kurtosis: -0.989098
skewness: -0.146725
entropy: 0.837577
Blue:
min: 0 (0)
max: 192 (0.752941)
mean: 66.7367 (0.261712)
standard deviation: 73.2147 (0.287116)
kurtosis: -1.56751
skewness: 0.331185
entropy: 0.854702
Image statistics:
Overall:
min: 0 (0)
max: 224 (0.878431)
mean: 85.4888 (0.33525)
standard deviation: 81.8828 (0.321109)
kurtosis: -1.56309
skewness: 0.182395
entropy: 0.848994
Colors: 4
Histogram:
54389: ( 0, 0, 0) #000000 black
34183: ( 0,128, 0) #008000 green
61143: (192,128,128) #C08080 srgb(192,128,128)
17285: (224,224,192) #E0E0C0 srgb(224,224,192)
Colormap entries: 256
Colormap:
0: ( 0, 0, 0,255) #000000FF black
1: (128, 0, 0,255) #800000FF maroon
2: ( 0,128, 0,255) #008000FF green
3: (128,128, 0,255) #808000FF olive
4: ( 0, 0,128,255) #000080FF navy
5: (128, 0,128,255) #800080FF purple
6: ( 0,128,128,255) #008080FF teal
7: (128,128,128,255) #808080FF fractal
8: ( 64, 0, 0,255) #400000FF srgba(64,0,0,1)
9: (192, 0, 0,255) #C00000FF srgba(192,0,0,1)
10: ( 64,128, 0,255) #408000FF srgba(64,128,0,1)
11: (192,128, 0,255) #C08000FF srgba(192,128,0,1)
12: ( 64, 0,128,255) #400080FF srgba(64,0,128,1)
13: (192, 0,128,255) #C00080FF srgba(192,0,128,1)
14: ( 64,128,128,255) #408080FF srgba(64,128,128,1)
15: (192,128,128,255) #C08080FF srgba(192,128,128,1)
16: ( 0, 64, 0,255) #004000FF srgba(0,64,0,1)
17: (128, 64, 0,255) #804000FF srgba(128,64,0,1)
18: ( 0,192, 0,255) #00C000FF srgba(0,192,0,1)
19: (128,192, 0,255) #80C000FF srgba(128,192,0,1)
20: ( 0, 64,128,255) #004080FF srgba(0,64,128,1)
21: (128, 64,128,255) #804080FF srgba(128,64,128,1)
22: ( 0,192,128,255) #00C080FF srgba(0,192,128,1)
23: (128,192,128,255) #80C080FF srgba(128,192,128,1)
24: ( 64, 64, 0,255) #404000FF srgba(64,64,0,1)
25: (192, 64, 0,255) #C04000FF srgba(192,64,0,1)
26: ( 64,192, 0,255) #40C000FF srgba(64,192,0,1)
27: (192,192, 0,255) #C0C000FF srgba(192,192,0,1)
28: ( 64, 64,128,255) #404080FF srgba(64,64,128,1)
29: (192, 64,128,255) #C04080FF srgba(192,64,128,1)
30: ( 64,192,128,255) #40C080FF srgba(64,192,128,1)
31: (192,192,128,255) #C0C080FF srgba(192,192,128,1)
32: ( 0, 0, 64,255) #000040FF srgba(0,0,64,1)
33: (128, 0, 64,255) #800040FF srgba(128,0,64,1)
34: ( 0,128, 64,255) #008040FF srgba(0,128,64,1)
35: (128,128, 64,255) #808040FF srgba(128,128,64,1)
36: ( 0, 0,192,255) #0000C0FF srgba(0,0,192,1)
37: (128, 0,192,255) #8000C0FF srgba(128,0,192,1)
38: ( 0,128,192,255) #0080C0FF srgba(0,128,192,1)
39: (128,128,192,255) #8080C0FF srgba(128,128,192,1)
40: ( 64, 0, 64,255) #400040FF srgba(64,0,64,1)
41: (192, 0, 64,255) #C00040FF srgba(192,0,64,1)
42: ( 64,128, 64,255) #408040FF srgba(64,128,64,1)
43: (192,128, 64,255) #C08040FF srgba(192,128,64,1)
44: ( 64, 0,192,255) #4000C0FF srgba(64,0,192,1)
45: (192, 0,192,255) #C000C0FF srgba(192,0,192,1)
46: ( 64,128,192,255) #4080C0FF srgba(64,128,192,1)
47: (192,128,192,255) #C080C0FF srgba(192,128,192,1)
48: ( 0, 64, 64,255) #004040FF srgba(0,64,64,1)
49: (128, 64, 64,255) #804040FF srgba(128,64,64,1)
50: ( 0,192, 64,255) #00C040FF srgba(0,192,64,1)
51: (128,192, 64,255) #80C040FF srgba(128,192,64,1)
52: ( 0, 64,192,255) #0040C0FF srgba(0,64,192,1)
53: (128, 64,192,255) #8040C0FF srgba(128,64,192,1)
54: ( 0,192,192,255) #00C0C0FF srgba(0,192,192,1)
55: (128,192,192,255) #80C0C0FF srgba(128,192,192,1)
56: ( 64, 64, 64,255) #404040FF grey25
57: (192, 64, 64,255) #C04040FF srgba(192,64,64,1)
58: ( 64,192, 64,255) #40C040FF srgba(64,192,64,1)
59: (192,192, 64,255) #C0C040FF srgba(192,192,64,1)
60: ( 64, 64,192,255) #4040C0FF srgba(64,64,192,1)
61: (192, 64,192,255) #C040C0FF srgba(192,64,192,1)
62: ( 64,192,192,255) #40C0C0FF srgba(64,192,192,1)
63: (192,192,192,255) #C0C0C0FF silver
64: ( 32, 0, 0,255) #200000FF srgba(32,0,0,1)
65: (160, 0, 0,255) #A00000FF srgba(160,0,0,1)
66: ( 32,128, 0,255) #208000FF srgba(32,128,0,1)
67: (160,128, 0,255) #A08000FF srgba(160,128,0,1)
68: ( 32, 0,128,255) #200080FF srgba(32,0,128,1)
69: (160, 0,128,255) #A00080FF srgba(160,0,128,1)
70: ( 32,128,128,255) #208080FF srgba(32,128,128,1)
71: (160,128,128,255) #A08080FF srgba(160,128,128,1)
72: ( 96, 0, 0,255) #600000FF srgba(96,0,0,1)
73: (224, 0, 0,255) #E00000FF srgba(224,0,0,1)
74: ( 96,128, 0,255) #608000FF srgba(96,128,0,1)
75: (224,128, 0,255) #E08000FF srgba(224,128,0,1)
76: ( 96, 0,128,255) #600080FF srgba(96,0,128,1)
77: (224, 0,128,255) #E00080FF srgba(224,0,128,1)
78: ( 96,128,128,255) #608080FF srgba(96,128,128,1)
79: (224,128,128,255) #E08080FF srgba(224,128,128,1)
80: ( 32, 64, 0,255) #204000FF srgba(32,64,0,1)
81: (160, 64, 0,255) #A04000FF srgba(160,64,0,1)
82: ( 32,192, 0,255) #20C000FF srgba(32,192,0,1)
83: (160,192, 0,255) #A0C000FF srgba(160,192,0,1)
84: ( 32, 64,128,255) #204080FF srgba(32,64,128,1)
85: (160, 64,128,255) #A04080FF srgba(160,64,128,1)
86: ( 32,192,128,255) #20C080FF srgba(32,192,128,1)
87: (160,192,128,255) #A0C080FF srgba(160,192,128,1)
88: ( 96, 64, 0,255) #604000FF srgba(96,64,0,1)
89: (224, 64, 0,255) #E04000FF srgba(224,64,0,1)
90: ( 96,192, 0,255) #60C000FF srgba(96,192,0,1)
91: (224,192, 0,255) #E0C000FF srgba(224,192,0,1)
92: ( 96, 64,128,255) #604080FF srgba(96,64,128,1)
93: (224, 64,128,255) #E04080FF srgba(224,64,128,1)
94: ( 96,192,128,255) #60C080FF srgba(96,192,128,1)
95: (224,192,128,255) #E0C080FF srgba(224,192,128,1)
96: ( 32, 0, 64,255) #200040FF srgba(32,0,64,1)
97: (160, 0, 64,255) #A00040FF srgba(160,0,64,1)
98: ( 32,128, 64,255) #208040FF srgba(32,128,64,1)
99: (160,128, 64,255) #A08040FF srgba(160,128,64,1)
100: ( 32, 0,192,255) #2000C0FF srgba(32,0,192,1)
101: (160, 0,192,255) #A000C0FF srgba(160,0,192,1)
102: ( 32,128,192,255) #2080C0FF srgba(32,128,192,1)
103: (160,128,192,255) #A080C0FF srgba(160,128,192,1)
104: ( 96, 0, 64,255) #600040FF srgba(96,0,64,1)
105: (224, 0, 64,255) #E00040FF srgba(224,0,64,1)
106: ( 96,128, 64,255) #608040FF srgba(96,128,64,1)
107: (224,128, 64,255) #E08040FF srgba(224,128,64,1)
108: ( 96, 0,192,255) #6000C0FF srgba(96,0,192,1)
109: (224, 0,192,255) #E000C0FF srgba(224,0,192,1)
110: ( 96,128,192,255) #6080C0FF srgba(96,128,192,1)
111: (224,128,192,255) #E080C0FF srgba(224,128,192,1)
112: ( 32, 64, 64,255) #204040FF srgba(32,64,64,1)
113: (160, 64, 64,255) #A04040FF srgba(160,64,64,1)
114: ( 32,192, 64,255) #20C040FF srgba(32,192,64,1)
115: (160,192, 64,255) #A0C040FF srgba(160,192,64,1)
116: ( 32, 64,192,255) #2040C0FF srgba(32,64,192,1)
117: (160, 64,192,255) #A040C0FF srgba(160,64,192,1)
118: ( 32,192,192,255) #20C0C0FF srgba(32,192,192,1)
119: (160,192,192,255) #A0C0C0FF srgba(160,192,192,1)
120: ( 96, 64, 64,255) #604040FF srgba(96,64,64,1)
121: (224, 64, 64,255) #E04040FF srgba(224,64,64,1)
122: ( 96,192, 64,255) #60C040FF srgba(96,192,64,1)
123: (224,192, 64,255) #E0C040FF srgba(224,192,64,1)
124: ( 96, 64,192,255) #6040C0FF srgba(96,64,192,1)
125: (224, 64,192,255) #E040C0FF srgba(224,64,192,1)
126: ( 96,192,192,255) #60C0C0FF srgba(96,192,192,1)
127: (224,192,192,255) #E0C0C0FF srgba(224,192,192,1)
128: ( 0, 32, 0,255) #002000FF srgba(0,32,0,1)
129: (128, 32, 0,255) #802000FF srgba(128,32,0,1)
130: ( 0,160, 0,255) #00A000FF srgba(0,160,0,1)
131: (128,160, 0,255) #80A000FF srgba(128,160,0,1)
132: ( 0, 32,128,255) #002080FF srgba(0,32,128,1)
133: (128, 32,128,255) #802080FF srgba(128,32,128,1)
134: ( 0,160,128,255) #00A080FF srgba(0,160,128,1)
135: (128,160,128,255) #80A080FF srgba(128,160,128,1)
136: ( 64, 32, 0,255) #402000FF srgba(64,32,0,1)
137: (192, 32, 0,255) #C02000FF srgba(192,32,0,1)
138: ( 64,160, 0,255) #40A000FF srgba(64,160,0,1)
139: (192,160, 0,255) #C0A000FF srgba(192,160,0,1)
140: ( 64, 32,128,255) #402080FF srgba(64,32,128,1)
141: (192, 32,128,255) #C02080FF srgba(192,32,128,1)
142: ( 64,160,128,255) #40A080FF srgba(64,160,128,1)
143: (192,160,128,255) #C0A080FF srgba(192,160,128,1)
144: ( 0, 96, 0,255) #006000FF srgba(0,96,0,1)
145: (128, 96, 0,255) #806000FF srgba(128,96,0,1)
146: ( 0,224, 0,255) #00E000FF srgba(0,224,0,1)
147: (128,224, 0,255) #80E000FF srgba(128,224,0,1)
148: ( 0, 96,128,255) #006080FF srgba(0,96,128,1)
149: (128, 96,128,255) #806080FF srgba(128,96,128,1)
150: ( 0,224,128,255) #00E080FF srgba(0,224,128,1)
151: (128,224,128,255) #80E080FF srgba(128,224,128,1)
152: ( 64, 96, 0,255) #406000FF srgba(64,96,0,1)
153: (192, 96, 0,255) #C06000FF srgba(192,96,0,1)
154: ( 64,224, 0,255) #40E000FF srgba(64,224,0,1)
155: (192,224, 0,255) #C0E000FF srgba(192,224,0,1)
156: ( 64, 96,128,255) #406080FF srgba(64,96,128,1)
157: (192, 96,128,255) #C06080FF srgba(192,96,128,1)
158: ( 64,224,128,255) #40E080FF srgba(64,224,128,1)
159: (192,224,128,255) #C0E080FF srgba(192,224,128,1)
160: ( 0, 32, 64,255) #002040FF srgba(0,32,64,1)
161: (128, 32, 64,255) #802040FF srgba(128,32,64,1)
162: ( 0,160, 64,255) #00A040FF srgba(0,160,64,1)
163: (128,160, 64,255) #80A040FF srgba(128,160,64,1)
164: ( 0, 32,192,255) #0020C0FF srgba(0,32,192,1)
165: (128, 32,192,255) #8020C0FF srgba(128,32,192,1)
166: ( 0,160,192,255) #00A0C0FF srgba(0,160,192,1)
167: (128,160,192,255) #80A0C0FF srgba(128,160,192,1)
168: ( 64, 32, 64,255) #402040FF srgba(64,32,64,1)
169: (192, 32, 64,255) #C02040FF srgba(192,32,64,1)
170: ( 64,160, 64,255) #40A040FF srgba(64,160,64,1)
171: (192,160, 64,255) #C0A040FF srgba(192,160,64,1)
172: ( 64, 32,192,255) #4020C0FF srgba(64,32,192,1)
173: (192, 32,192,255) #C020C0FF srgba(192,32,192,1)
174: ( 64,160,192,255) #40A0C0FF srgba(64,160,192,1)
175: (192,160,192,255) #C0A0C0FF srgba(192,160,192,1)
176: ( 0, 96, 64,255) #006040FF srgba(0,96,64,1)
177: (128, 96, 64,255) #806040FF srgba(128,96,64,1)
178: ( 0,224, 64,255) #00E040FF srgba(0,224,64,1)
179: (128,224, 64,255) #80E040FF srgba(128,224,64,1)
180: ( 0, 96,192,255) #0060C0FF srgba(0,96,192,1)
181: (128, 96,192,255) #8060C0FF srgba(128,96,192,1)
182: ( 0,224,192,255) #00E0C0FF srgba(0,224,192,1)
183: (128,224,192,255) #80E0C0FF srgba(128,224,192,1)
184: ( 64, 96, 64,255) #406040FF srgba(64,96,64,1)
185: (192, 96, 64,255) #C06040FF srgba(192,96,64,1)
186: ( 64,224, 64,255) #40E040FF srgba(64,224,64,1)
187: (192,224, 64,255) #C0E040FF srgba(192,224,64,1)
188: ( 64, 96,192,255) #4060C0FF srgba(64,96,192,1)
189: (192, 96,192,255) #C060C0FF srgba(192,96,192,1)
190: ( 64,224,192,255) #40E0C0FF srgba(64,224,192,1)
191: (192,224,192,255) #C0E0C0FF srgba(192,224,192,1)
192: ( 32, 32, 0,255) #202000FF srgba(32,32,0,1)
193: (160, 32, 0,255) #A02000FF srgba(160,32,0,1)
194: ( 32,160, 0,255) #20A000FF srgba(32,160,0,1)
195: (160,160, 0,255) #A0A000FF srgba(160,160,0,1)
196: ( 32, 32,128,255) #202080FF srgba(32,32,128,1)
197: (160, 32,128,255) #A02080FF srgba(160,32,128,1)
198: ( 32,160,128,255) #20A080FF srgba(32,160,128,1)
199: (160,160,128,255) #A0A080FF srgba(160,160,128,1)
200: ( 96, 32, 0,255) #602000FF srgba(96,32,0,1)
201: (224, 32, 0,255) #E02000FF srgba(224,32,0,1)
202: ( 96,160, 0,255) #60A000FF srgba(96,160,0,1)
203: (224,160, 0,255) #E0A000FF srgba(224,160,0,1)
204: ( 96, 32,128,255) #602080FF srgba(96,32,128,1)
205: (224, 32,128,255) #E02080FF srgba(224,32,128,1)
206: ( 96,160,128,255) #60A080FF srgba(96,160,128,1)
207: (224,160,128,255) #E0A080FF srgba(224,160,128,1)
208: ( 32, 96, 0,255) #206000FF srgba(32,96,0,1)
209: (160, 96, 0,255) #A06000FF srgba(160,96,0,1)
210: ( 32,224, 0,255) #20E000FF srgba(32,224,0,1)
211: (160,224, 0,255) #A0E000FF srgba(160,224,0,1)
212: ( 32, 96,128,255) #206080FF srgba(32,96,128,1)
213: (160, 96,128,255) #A06080FF srgba(160,96,128,1)
214: ( 32,224,128,255) #20E080FF srgba(32,224,128,1)
215: (160,224,128,255) #A0E080FF srgba(160,224,128,1)
216: ( 96, 96, 0,255) #606000FF srgba(96,96,0,1)
217: (224, 96, 0,255) #E06000FF srgba(224,96,0,1)
218: ( 96,224, 0,255) #60E000FF srgba(96,224,0,1)
219: (224,224, 0,255) #E0E000FF srgba(224,224,0,1)
220: ( 96, 96,128,255) #606080FF srgba(96,96,128,1)
221: (224, 96,128,255) #E06080FF srgba(224,96,128,1)
222: ( 96,224,128,255) #60E080FF srgba(96,224,128,1)
223: (224,224,128,255) #E0E080FF srgba(224,224,128,1)
224: ( 32, 32, 64,255) #202040FF srgba(32,32,64,1)
225: (160, 32, 64,255) #A02040FF srgba(160,32,64,1)
226: ( 32,160, 64,255) #20A040FF srgba(32,160,64,1)
227: (160,160, 64,255) #A0A040FF srgba(160,160,64,1)
228: ( 32, 32,192,255) #2020C0FF srgba(32,32,192,1)
229: (160, 32,192,255) #A020C0FF srgba(160,32,192,1)
230: ( 32,160,192,255) #20A0C0FF srgba(32,160,192,1)
231: (160,160,192,255) #A0A0C0FF srgba(160,160,192,1)
232: ( 96, 32, 64,255) #602040FF srgba(96,32,64,1)
233: (224, 32, 64,255) #E02040FF srgba(224,32,64,1)
234: ( 96,160, 64,255) #60A040FF srgba(96,160,64,1)
235: (224,160, 64,255) #E0A040FF srgba(224,160,64,1)
236: ( 96, 32,192,255) #6020C0FF srgba(96,32,192,1)
237: (224, 32,192,255) #E020C0FF srgba(224,32,192,1)
238: ( 96,160,192,255) #60A0C0FF srgba(96,160,192,1)
239: (224,160,192,255) #E0A0C0FF srgba(224,160,192,1)
240: ( 32, 96, 64,255) #206040FF srgba(32,96,64,1)
241: (160, 96, 64,255) #A06040FF srgba(160,96,64,1)
242: ( 32,224, 64,255) #20E040FF srgba(32,224,64,1)
243: (160,224, 64,255) #A0E040FF srgba(160,224,64,1)
244: ( 32, 96,192,255) #2060C0FF srgba(32,96,192,1)
245: (160, 96,192,255) #A060C0FF srgba(160,96,192,1)
246: ( 32,224,192,255) #20E0C0FF srgba(32,224,192,1)
247: (160,224,192,255) #A0E0C0FF srgba(160,224,192,1)
248: ( 96, 96, 64,255) #606040FF srgba(96,96,64,1)
249: (224, 96, 64,255) #E06040FF srgba(224,96,64,1)
250: ( 96,224, 64,255) #60E040FF srgba(96,224,64,1)
251: (224,224, 64,255) #E0E040FF srgba(224,224,64,1)
252: ( 96, 96,192,255) #6060C0FF srgba(96,96,192,1)
253: (224, 96,192,255) #E060C0FF srgba(224,96,192,1)
254: ( 96,224,192,255) #60E0C0FF srgba(96,224,192,1)
255: (224,224,192,255) #E0E0C0FF srgba(224,224,192,1) <--- THIS LINE
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