python读取二进制mnist

Posted 2020-09-20

training data 数据结构：

[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

 

 

 将整个文件读入：

filename = ‘train-images.idx3-ubyte‘
binfile = open(filename , ‘rb‘)
buf = binfile.read()

 

读取头四个32bit的interger:

index = 0
magic, numImages , numRows , numColumns = struct.unpack_from(‘>IIII‘ , buf , index)
index += struct.calcsize(‘>IIII‘)

 

读取一个图片，784=28*28 ：

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()