其实就是python怎么读取binnary file
mnist的结构如下，选取train-images
TRAINING SET IMAGE FILE (train-images-idx3-ubyte):
[offset] [type] [value] [description]
0000 32 bit integer 0x00000803(2051) magic number
0004 32 bit integer 60000 number of images
0008 32 bit integer 28 number of rows
0012 32 bit integer 28 number of columns
0016 unsigned byte ?? pixel
0017 unsigned byte ?? pixel
........
xxxx unsigned byte ?? pixel
也就是之前我们要读取4个 32 bit integer
试过很多方法，觉得最方便的，至少对我来说还是使用
struct.unpack_from()
filename = 'train-images.idx3-ubyte'
binfile = open(filename , 'rb')
buf = binfile.read()
先使用二进制方式把文件都读进来
index = 0
magic, numImages , numRows , numColumns = struct.unpack_from('>IIII' , buf , index)
index += struct.calcsize('>IIII')
然后使用struc.unpack_from
'>IIII'是说使用大端法读取4个unsinged int32
然后读取一个图片测试是否读取成功
im = struct.unpack_from('>784B' ,buf, index)
index += struct.calcsize('>784B')
im = np.array(im)
im = im.reshape(28,28)
fig = plt.figure()
plotwindow = fig.add_subplot(111)
plt.imshow(im , cmap='gray')
plt.show()
'>784B'的意思就是用大端法读取784个unsigned byte
完整代码如下
import numpy as np
import struct
import matplotlib.pyplot as plt
filename = 'train-images.idx3-ubyte'
binfile = open(filename , 'rb')
buf = binfile.read()
index = 0
magic, numImages , numRows , numColumns = struct.unpack_from('>IIII' , buf , index)
index += struct.calcsize('>IIII')
im = struct.unpack_from('>784B' ,buf, index)
index += struct.calcsize('>784B')
im = np.array(im)
im = im.reshape(28,28)
fig = plt.figure()
plotwindow = fig.add_subplot(111)
plt.imshow(im , cmap='gray')
plt.show()
只是为了测试是否成功所以只读了一张图片
