Numpy basic learning

numpy Bottom use c Language , Calculate around an array , Default 64 Bit floating point

np.array()

np.zeros()

np.ones()

np.shape()

np.arange()

np.random.rand()

Convert data type

1. Creation time

b=np.zeros((2,3),dtype=np.int32)

np.int8/16/32/64

np.uint8/16/32/64

np.float32/64

bool

str

2. Created

a=a.astype(int)

Basic operation

1. arithmetic

Same size ：

a=np.array([1,2,3,4])

b=np.array([5,4,3,2])

Different sizes ：

a=np.array([[1],

                    [2]])

b=np.array([5,4])

 

hold a The array consists of

1

2

Expanded into

1	1
2	2

2. Other mathematical operations

square root , logarithmic , Index of operation , Sine, etc

np.sqrt(a)

np.log(a)

np.pow(a,3)

np.sin(a)

Filter elements

b[(b>3)&(b%2==0)]

  a=np.array([[1,2],[3,4]]）

 a[1,:]

 

  Typical applications - The image processing

1. Read the picture

from PIL import Image

im=Image.open('F:\\ desktop \\flower.jpg')

im.show

 2. Convert images to arrays

im=np.array(im)

im.shape

 3. cut picture

im1=np.array(Image.open('F:\\ desktop \\flower.jpg'))

im2=np.array(Image.open('F:\\ desktop \\yellow.jpg'))

im1_cropped=im1[:600,:1000,:]

im2_cropped=im2[:600,:1000,:]

Image.fromarray(im1_cropped).show()

Image.fromarray(im2_cropped).show()

 

4. Mix two pictures

im_blend=im1_cropped*0.2+im2_cropped*0.5

im_blend=im_blend.astype(np.uint8)

Image.fromarray(im_blend).show()

5. Rollover Image

im1_fliepped=im1[::-1,:,:]

Image.fromarray(im1_fliepped).show()