# coding: utf-8
import numpy as np
np.__version__
a = np.zeros((3, 3))
a
a = np.ones((3, 3))
a
a.shape
a.dtype
a = np.array([1,2,3])
a
a = np.array(range(9))
a
a = np.arange(0, 12)
a
b = a.reshape((3, 4))
b
a.dtype
a = a.astype(np.float64)
a
a.dtype
b
b = b.astype(np.float32)
b.dtype
a[0]
a
a[0]
a[1:4]
a[:4]
a[4:]
a[:]
a
a[:]
b
b[1,0]
b[1,0]
b[1,:]
b[:,1]
b[:2, :]
b
b[1:3, 1:3]
b - 4
b * b
b**2
np.sum(b)
np.min(b)
np.max(b)
np.mean(b)
np.sum(b, axis=1)
b
np.sum(b, axis=0)
a = np.ones((500,500), dtype=np.float32)
a
def f1(arr):
    return a + 5
def f1(arr):
    return arr + 5
def f2(arr):
    h, w = arr.shape
    for i in range(h):
        for j in range(w):
            arr[i,j] += 5
            
a
get_ipython().magic('time f1(a)')
get_ipython().magic('time f2(a)')
a
b
np.pad(b, 2, 'constant', cval=0)
np.pad(b, 2, 'constant')
x = np.array([1,2,2,3])
x.dot(x)
I = np.eye(4)
I
I.dot(x)
import cv2
van = cv2.imread("van.png")
van.shape
cv2.imwrite("van_out.png", van)
van_blue = van[:,:,0]
cv2.imwrite("van_blue.png", van_blue)
van.dtype
van = van.astype(np.float32) / 2555
van.min()
van.max()
van *= 2555
van /= 255
van.max()
van *= 1.2
van_out = (van * 255).clip(0, 255).astype(np.uint8)
cv2.imwrite("van_adj.png", van_out)