Paul Parneix Paul Parneix - 1 month ago 33
Python Question

reading middlebury 'flow' files with python (bytes array & numpy)

I'm trying to read a .flo file as a numpy 2Channels image.

The format is described like this:



".flo" file format used for optical flow evaluation

Stores 2-band float image for horizontal (u) and vertical (v) flow components.
Floats are stored in little-endian order.
A flow value is considered "unknown" if either |u| or |v| is greater than 1e9.

bytes contents

0-3 tag: "PIEH" in ASCII, which in little endian happens to be the float 202021.25
(just a sanity check that floats are represented correctly)
4-7 width as an integer
8-11 height as an integer
12-end data (width*height*2*4 bytes total)
the float values for u and v, interleaved, in row order, i.e.,
u[row0,col0], v[row0,col0], u[row0,col1], v[row0,col1], ...


(Excerpt from this readme)

Here's my code but I'm kind of stuck, I don't know how to read the file as a 2 Channels numpy 2D array.

import numpy as np
import os

# test.flo, 512*512 optical flow file

f = open('test.flo', 'rb')
f.seek(11, os.SEEK_SET) # skip header bytes


data_array = np.fromfile(f, np.float16)
data_2D = np.resize(data_array, (512, 512))


Maybe someone knows how to do that ?

bsa bsa
Answer

Try this. I've tested it on one .flo file so far.

import numpy as np
import os
import sys

# WARNING: this will work on little-endian architectures (eg Intel x86) only!
if '__main__' == __name__:
    if len(sys.argv) > 1:
        with open(sys.argv[1], 'rb') as f:
            magic = np.fromfile(f, np.float32, count=1)
            if 202021.25 != magic:
                print 'Magic number incorrect. Invalid .flo file'
            else:
                w = np.fromfile(f, np.int32, count=1)
                h = np.fromfile(f, np.int32, count=1)
                print 'Reading %d x %d flo file' % (w, h)
                data = np.fromfile(f, np.float32, count=2*w*h)
                # Reshape data into 3D array (columns, rows, bands)
                data2D = np.resize(data, (w, h, 2))
    else:
        print 'Specify a .flo file on the command line.'
Comments