CODEWITHSUNDEEP
pythonscikit-image
Adam Cherti
Adam Cherti

Reputation: 982

Skimage : rotate image and fill the new formed background

When rotating an image using

import skimage

result = skimage.transform.rotate(img, angle=some_angle, resize=True)
# the result is the rotated image with black 'margins' that fill the blanks

The algorithm rotates the image but leaves the newly formed background black and there is no way - using the rotate function - to choose the color of the newly formed background.

Do you have any idea how to do choose the color of the background before rotating an image?

Thank you.

Upvotes: 3

Views: 3749

Answers (5)

c yipkwun
c yipkwun

Reputation: 41

tbh I don't know why everyone set the cval value to a strange value.
I think it's intuitive when you look at the documentation of the function

cval : float, optional
Used in conjunction with mode ‘constant’, the value outside the image boundaries.

Therefore depending on what your input image is, in my case, my picture already used cv2.cvtColor(img, cv2.COLOR_BGR2GRAY), therefore in order to set it to white, I can simply set cval=255.

If it's ndarray(img more than 1 channel), you can either rotate each channel separately, or set it to strange value then use np.where to replace afterward. (idk why but I just don't like this method lol)

Upvotes: 0

Warren
Warren

Reputation: 21

It's a little annoying that the cval parameter to skimage.transform.warp() can only be a scalar float.

You can set it to any value outside of the range of your data (like -1), and use np.where() to fix it afterwards. Here's an example that sets the background of a 3-channel image to red:

output = tf.warp(image, tform, mode='constant', cval=-1,
                 preserve_range=True, output_shape=(256, 256), order=3)
w = np.where(output == -1)
output[w[0], w[1], :] = [255, 0, 0]

Upvotes: 2

ttoporau
ttoporau

Reputation: 61

Just use cval parameter

img3 = transform.rotate(img20, 45, resize=True, cval=1, mode ='constant')
img4 = img3 * 255

Upvotes: 6

kiviak
kiviak

Reputation: 1103

if your pic is a gray picture,use cval ; if pic is rgb ,no good way,blow code works:

path3=r'C:\\Users\forfa\Downloads\1111.jpg'
img20=data.imread(path3)
import numpy as np
img3=transform.rotate(img20,45,resize=True,cval=0.1020544) #0.1020544 can be any unique float,the pixel outside your pic is [0.1020544]*3
c,r,k=img3.shape
for i in range(c):
    for j in range(r):
        if np.allclose(img3[i][j],[0.1020544]*3):
            img3[i][j]=[1,0,0]  #[1,0,0] is red pixel,replace pixel [0.1020544]*3  with red pixel [1,0,0]

Upvotes: -1

Yasser Batas
Yasser Batas

Reputation: 38

I don't know how do it, but maybe this help you 

http://scikit-image.org/docs/dev/api/skimage.color.html

Good luck! ;)

Upvotes: -2

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