Scipy 笔记

import numpy as np
from scipy.misc import imread, imsave, imresize
img = imread('data/chenhongqi3.jpg')
print(img.dtype, img.shape)
img_recolor = img * [1, 0.95, 0.9]
imsave('data/chenRecolor.jpg', img_recolor)
img_resize = imresize(img_recolor, (300,300))
imsave('data/chenRecolResize.jpg', img_resize)

uint8 (1920, 1280, 3)

scipy.spatial.distance.pdist input a matrix, return Euclidean dist of all rows

import numpy as np
from scipy.spatial.distance import pdist, squareform
x= np.array([[0, 1], [1, 0], [2, 0]])
print(x)

# Euclidean distance between allrows of x
print(pdist(x, 'euclidean'))
d= squareform(pdist(x, 'euclidean'))
print (d)

[[0 1]
 [1 0]
 [2 0]]
[1.41421356 2.23606798 1.        ]
[[0.         1.41421356 2.23606798]
 [1.41421356 0.         1.        ]
 [2.23606798 1.         0.        ]]

how is the result computed

row 0 dist row 0 ===> result[0,0]
row 0 dist row 1 ===> result[0,1]
row 0 dist row 2 ===> result[0,2]
row 1 dist row 0 ===> result[1,0]
row 1 dist row 1 ===> result[1,1]
row 1 dist row 2 ===> result[1,2]
row 2 dist row 0 ===> result[2,0]
row 2 dist row 1 ===> result[2,1]
row 2 dist row 2 ===> result[2,2]
---------------------------------------------
d[i,j] = x[i,:] dist x[j,:], for x,y = 0 to 3

scipy.spatial.distance.cdist

input 2 collections of points, compute every point from 1st collection to all points of 2nd collection

Note that, you can not apply squareform on the result of cdist, it's not an symmetric matrix

from scipy.spatial.distance import cdist, squareform
y1=np.array([[0, 1], [1, 0], [2, 0]])
y2=np.array([[3, 4], [4, 2], [2, 0]])

c = cdist(y1, y2, 'euclidean')
print (c)

[[4.24264069 4.12310563 2.23606798]
 [4.47213595 3.60555128 1.        ]
 [4.12310563 2.82842712 0.        ]]

.                [0,1]    [1,0]    [2,0]
.                 |
.                 |
.                 +---------+--------+
.                 |         |        |
.                 v         v        v
.                [3,4]    [4,2]    [2,0]
.
.result index    (0,0)    (0,1)    (0,2)