Shifting an image in numpy
14,672
Solution 1
There's no other way, as to handle negative and positive shifts accordingly:
non = lambda s: s if s<0 else None
mom = lambda s: max(0,s)
ox, oy = 100, 20
shift_lena = numpy.zeros_like(lena)
shift_lena[mom(oy):non(oy), mom(ox):non(ox)] = lena[mom(-oy):non(-oy), mom(-ox):non(-ox)]
Solution 2
You can use roll function to circular shift x and y and then zerofill the offset
def shift_image(X, dx, dy):
X = np.roll(X, dy, axis=0)
X = np.roll(X, dx, axis=1)
if dy>0:
X[:dy, :] = 0
elif dy<0:
X[dy:, :] = 0
if dx>0:
X[:, :dx] = 0
elif dx<0:
X[:, dx:] = 0
return X
Author by
Gert Gottschalk
Updated on July 16, 2022Comments
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Gert Gottschalk over 1 year
I have a image in a 2d numpy array. I want to shift the image by an X and Y offset and want the rest of the frame padded with zeros. I have seen discussions about the 'roll' function but that only works in 1 axis. (unless someone can point me to a 2d version with padding). I have tried slicing but I run into trouble when shifting offsets have all possible directions. I don't want to navigate through all X Y offset +/- permutations. Is there a simple general solution? I have the below code which works nice for X-offset=+100. But it crashes for X-offset=-100.
Thanks, Gert
import matplotlib.pyplot as plt import scipy.misc as msc import numpy as np lena = msc.lena() lena.dtype (imx,imy)= lena.shape ox= 100 oy= 20 shift_lena = np.zeros((imx,imy)) shift_lena[0:imy-oy,0:imx-ox] = lena[oy:,ox:] shift_lena_m = shift_lena.astype(np.int64) shift_lena_m.dtype plt.figure(figsize=(10, 3.6)) plt.subplot(131) plt.imshow(lena, cmap=plt.cm.gray) plt.subplot(132) plt.imshow(shift_lena_m, cmap=plt.cm.gray) plt.subplots_adjust(wspace=0, hspace=0., top=0.99, bottom=0.01, left=0.05, right=0.99) plt.show()