readFlowFile.py

#   compute colored image to visualize optical flow file .flo

#   According to the matlab code of Deqing Sun and c++ source code of Daniel Scharstein  
#   Contact: dqsun@cs.brown.edu
#   Contact: schar@middlebury.edu

#   Author: Johannes Oswald, Technical University Munich
#   Contact: johannes.oswald@tum.de
#   Date: 26/04/2017

#	For more information, check http://vision.middlebury.edu/flow/ 

import numpy as np
import os

TAG_FLOAT = 202021.25

def read_flow(file):

	assert type(file) is str, "file is not str %r" % str(file)
	assert os.path.isfile(file) is True, "file does not exist %r" % str(file)
	assert file[-4:] == '.flo', "file ending is not .flo %r" % file[-4:]
	f = open(file,'rb')
	flo_number = np.fromfile(f, np.float32, count=1)[0]
	assert flo_number == TAG_FLOAT, 'Flow number %r incorrect. Invalid .flo file' % flo_number
	w = np.fromfile(f, np.int32, count=1)
	h = np.fromfile(f, np.int32, count=1)
	data = np.fromfile(f, np.float32, count=2*w[0]*h[0])
	#if error try: data = np.fromfile(f, np.float32, count=2*w*h)
	# Reshape data into 3D array (columns, rows, bands)
	flow = np.resize(data, (int(h), int(w), 2))	
	f.close()

	return flow