Is the range param in calcHist() supposed to accept and correctly return counts for bins defined using negative float values? As an example, is the following a valid range definition for three dimensions?
range = [
0, 255,
-1 * np.pi, np.pi,
0.0, 255 * np.sqrt(2)
]
strann was right. calcHist() does appear to work with negative float32 values, so something else must've been the problem in my code. The simple script below demonstrates calcHist() applied to floating point values in an array, which I tested using Python 2.7.6 and OpenCV 3.1.0 (cv2.__version__).
import cv2
import numpy as np
def print_arr(arr, name='arr'):
print '{}({}):\n{}'.format(name, arr.dtype, arr)
if __name__ == '__main__':
# Define an arbitrary 3-D array
im = np.array(
[[[1.0, -50.3, 22.3], [-88.2, 30.1, 59.8]],
[[9.0, 50.3, -22.3], [ -8.2, 90.1, -9.8]]], dtype=np.float32)
print_arr(im, 'im')
# Define expected ranges
images = [im]
channels = [0, 1, 2]
mask = None
histSize = [3, 6, 12]
ranges = [
-180.0, 180.0,
-90.0, 270.0,
-45.0, 315.0
]
# Calculate the histogram
hist = cv2.calcHist(images, channels, mask, histSize, ranges)
print_arr(hist, 'hist')
Asked: 2016-03-21 19:13:22 -0600
Seen: 1,161 times
Last updated: Mar 23 '16
I believe it is, at least in C++ API
calcHist()works correctly with negative float values inrange