Source Code for Module fabio.readbytestream

 1  ## Automatically adapted for numpy.oldnumeric Oct 05, 2007 by alter_code1.py 
 2   
 3   
 4   
 5  """ 
 6  Reads a bytestream 
 7   
 8  Authors: Jon Wright    Henning O. Sorensen & Erik Knudsen 
 9           ESRF          Risoe National Laboratory 
10  """ 
11   
12  import numpy as N, logging 
13   
14  DATATYPES = { 
15      # type  sign bytes 
16      ("int", 'n', 1) : N.uint8, 
17      ("int", 'n', 2) : N.uint16, 
18      ("int", 'n', 4) : N.uint32, 
19      ("int", 'y', 1) : N.int8, 
20      ("int", 'y', 2) : N.int16, 
21      ("int", 'y', 4) : N.int32, 
22      ('float','y',4) : N.float32, # does this occur in bruker? 
23      ('double','y',4): N.float64 
24      } 
25   
26   
27 -def readbytestream(fil, 
28                     offset, 
29                     x, 
30                     y, 
31                     nbytespp, 
32                     datatype='int', 
33                     signed='n', 
34                     swap='n', 
35                     typeout=N.uint16): 
36      """ 
37      Reads in a bytestream from a file (which may be a string indicating 
38      a filename, or an already opened file (should be "rb")) 
39      offset is the position (in bytes) where the pixel data start 
40      nbytespp = number of bytes per pixel 
41      type can be int or float (4 bytes pp) or double (8 bytes pp) 
42      signed: normally signed data 'y', but 'n' to try to get back the  
43      right numbers when unsigned data are converted to signed  
44      (python once had no unsigned numeric types.) 
45      swap, normally do not bother, but 'y' to swap bytes 
46      typeout is the numpy type to output, normally uint16,  
47      but more if overflows occurred 
48      x and y are the pixel dimensions 
49       
50      TODO : Read in regions of interest 
51       
52      PLEASE LEAVE THE STRANGE INTERFACE ALONE -  
53      IT IS USEFUL FOR THE BRUKER FORMAT 
54      """ 
55      tin = "dunno" 
56      length = nbytespp * x * y # bytes per pixel times number of pixels 
57      if datatype in ['float', 'double']: 
58          signed = 'y' 
59   
60      key = (datatype, signed, nbytespp) 
61      try: 
62          tin = DATATYPES[key] 
63      except: 
64          logging.warning("datatype,signed,nbytespp "+str(key)) 
65          raise Exception("Unknown combination of types to readbytestream") 
66   
67      # Did we get a string (filename) or a readable stream object? 
68      if hasattr(fil,"read") and hasattr(fil,"seek"): 
69          infile = fil 
70          opened = False 
71      else: 
72          infile = open(fil,'rb') 
73          opened = True 
74   
75      infile.seek(offset) 
76   
77      arr = N.array(N.reshape( 
78              N.fromstring( 
79                  infile.read(length), tin) ,(x, y)),typeout) 
80   
81      if swap == 'y': 
82          arr = arr.byteswap() 
83   
84      if opened: 
85          infile.close() 
86   
87      return arr 
88