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# Flow visualization code used from https://github.com/tomrunia/OpticalFlow_Visualization
# MIT License
#
# Copyright (c) 2018 Tom Runia
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to conditions.
#
# Author: Tom Runia
# Date Created: 2018-08-03
import numpy as np
import torch
def make_colorwheel():
"""
Generates a color wheel for optical flow visualization as presented in:
Baker et al. "A Database and Evaluation Methodology for Optical Flow" (ICCV, 2007)
URL: http://vision.middlebury.edu/flow/flowEval-iccv07.pdf
Code follows the original C++ source code of Daniel Scharstein.
Code follows the the Matlab source code of Deqing Sun.
Returns:
np.ndarray: Color wheel
"""
RY = 15
YG = 6
GC = 4
CB = 11
BM = 13
MR = 6
ncols = RY + YG + GC + CB + BM + MR
colorwheel = np.zeros((ncols, 3))
col = 0
# RY
colorwheel[0:RY, 0] = 255
colorwheel[0:RY, 1] = np.floor(255*np.arange(0, RY)/RY)
col = col+RY
# YG
colorwheel[col:col+YG, 0] = 255 - np.floor(255*np.arange(0, YG)/YG)
colorwheel[col:col+YG, 1] = 255
col = col+YG
# GC
colorwheel[col:col+GC, 1] = 255
colorwheel[col:col+GC, 2] = np.floor(255*np.arange(0, GC)/GC)
col = col+GC
# CB
colorwheel[col:col+CB, 1] = 255 - np.floor(255*np.arange(CB)/CB)
colorwheel[col:col+CB, 2] = 255
col = col+CB
# BM
colorwheel[col:col+BM, 2] = 255
colorwheel[col:col+BM, 0] = np.floor(255*np.arange(0, BM)/BM)
col = col+BM
# MR
colorwheel[col:col+MR, 2] = 255 - np.floor(255*np.arange(MR)/MR)
colorwheel[col:col+MR, 0] = 255
return colorwheel
def flow_uv_to_colors(u, v, convert_to_bgr=False):
"""
Applies the flow color wheel to (possibly clipped) flow components u and v.
According to the C++ source code of Daniel Scharstein
According to the Matlab source code of Deqing Sun
Args:
u (np.ndarray): Input horizontal flow of shape [H,W]
v (np.ndarray): Input vertical flow of shape [H,W]
convert_to_bgr (bool, optional): Convert output image to BGR. Defaults to False.
Returns:
np.ndarray: Flow visualization image of shape [H,W,3]
"""
flow_image = np.zeros((u.shape[0], u.shape[1], 3), np.uint8)
colorwheel = make_colorwheel() # shape [55x3]
ncols = colorwheel.shape[0]
rad = np.sqrt(np.square(u) + np.square(v))
a = np.arctan2(-v, -u)/np.pi
fk = (a+1) / 2*(ncols-1)
k0 = np.floor(fk).astype(np.int32)
k1 = k0 + 1
k1[k1 == ncols] = 0
f = fk - k0
for i in range(colorwheel.shape[1]):
tmp = colorwheel[:, i]
col0 = tmp[k0] / 255.0
col1 = tmp[k1] / 255.0
col = (1-f)*col0 + f*col1
idx = (rad <= 1)
col[idx] = 1 - rad[idx] * (1-col[idx])
col[~idx] = col[~idx] * 0.75 # out of range
# Note the 2-i => BGR instead of RGB
ch_idx = 2-i if convert_to_bgr else i
flow_image[:, :, ch_idx] = np.floor(255 * col)
return flow_image
def flow_to_image(flow_uv, clip_flow=None, convert_to_bgr=False, normalize=True):
"""
Expects a two dimensional flow image of shape.
Args:
flow_uv (np.ndarray): Flow UV image of shape [H,W,2]
clip_flow (float, optional): Clip maximum of flow values. Defaults to None.
convert_to_bgr (bool, optional): Convert output image to BGR. Defaults to False.
Returns:
np.ndarray: Flow visualization image of shape [H,W,3]
"""
assert flow_uv.ndim == 3, 'input flow must have three dimensions'
assert flow_uv.shape[2] == 2, 'input flow must have shape [H,W,2]'
if clip_flow is not None:
flow_uv = np.clip(flow_uv, 0, clip_flow)
u = flow_uv[:, :, 0]
v = flow_uv[:, :, 1]
if normalize:
rad = np.sqrt(np.square(u) + np.square(v))
rad_max = np.max(rad)
else:
rad_max = np.sqrt(flow_uv.shape[0] ** 2 + flow_uv.shape[0] ** 2)
epsilon = 1e-5
u = u / (rad_max + epsilon)
v = v / (rad_max + epsilon)
return flow_uv_to_colors(u, v, convert_to_bgr)
def flow_batch_to_images(flow_uv, clip_flow=None, convert_to_bgr=False, normalize=True):
flows = [flow_to_image(f.detach().cpu().numpy(), clip_flow, convert_to_bgr, normalize) for f in flow_uv.permute(0, 2, 3, 1)]
flows = torch.cat([torch.from_numpy(f).unsqueeze(0) for f in flows], dim=0)
return flows.to(flow_uv.device).permute(0, 3, 1, 2) / 255.0
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