animation/fourcell/notes/brute_force_scale_invariant...

81 lines
2.8 KiB
Python

import math
import numpy
import scipy.ndimage
import imagecodecs
import imreg
from matplotlib import pyplot, patches
def brute_force_scale_invariant_template_matching(
template, # grayscale image
search, # scaled and cropped grayscale image
zooms=(1.0, 0.5, 0.25), # sequence of zoom factors to try
size=None, # power-of-two size of square sliding window
delta=None, # advance of sliding windows. default: half window size
min_overlap=0.25, # minimum overlap of search with window
max_diff=0.05, # max average of search - window differences in overlap
max_angle=0.5, # no rotation
):
"""Return yoffset, xoffset, and scale of first match of search in template.
Iterate over scaled versions of the template image in overlapping sliding
windows and run FFT-based algorithm for translation, rotation and
scale-invariant image registration until a match of the search image is
found in the sliding window.
"""
if size is None:
size = int(pow(2, int(math.log(min(search.shape), 2))))
if delta is None:
delta = size // 2
search = search[:size, :size]
for zoom in zooms:
windows = numpy.lib.stride_tricks.sliding_window_view(
scipy.ndimage.zoom(template, zoom), search.shape
)[::delta, ::delta]
for i in range(windows.shape[0]):
for j in range(windows.shape[1]):
print('.', end='')
window = windows[i, j]
im2, scale, angle, (t0, t1) = imreg.similarity(window, search)
diff = numpy.abs(im2 - window)[im2 != 0]
if (
abs(angle) < max_angle
and diff.size / window.size > min_overlap
and numpy.mean(diff) < max_diff
):
return (
(i * delta - t0) / zoom,
(j * delta - t1) / zoom,
1 / scale / zoom,
)
raise ValueError('no match of search image found in template')
def rgb2gray(rgb, scale=None):
"""Return float grayscale image from RGB24 or RGB48 image."""
scale = numpy.iinfo(rgb.dtype).max if scale is None else scale
scale = numpy.array([[[0.299, 0.587, 0.114]]], numpy.float32) / scale
return numpy.sum(rgb * scale, axis=-1)
template = imagecodecs.imread('cw1_IMG_9037.jpg')
search = imagecodecs.imread('cw1_p1_9037_kzw.jpg')
yoffset, xoffset, scale = brute_force_scale_invariant_template_matching(
rgb2gray(template), rgb2gray(search), zooms=(0.5,)
)
print(yoffset, xoffset, scale)
figure, ax = pyplot.subplots()
ax.imshow(template)
rect = patches.Rectangle(
(xoffset, yoffset),
scale * search.shape[1],
scale * search.shape[0],
linewidth=1,
edgecolor='r',
facecolor='none',
)
ax.add_patch(rect)
pyplot.show()