Load imageΒΆ
| Date: | 2008-12-08 (last modified), 2006-10-10 (created) |
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Image processing often works on gray scale images that were stored as PNG files. How do we import / export that file into {{{python}}}?
- Here is a recipy to do this with Matplotlib using the {{{imread}}} function (your image is called {{{lena.png}}}).
from pylab import imread, imshow, gray, mean
a = imread('lena.png')
# generates a RGB image, so do
aa=mean(a,2) # to get a 2-D array
imshow(aa)
gray()
This permits to do some processing for further exporting such as for [:Cookbook/Matplotlib/converting_a_matrix_to_a_raster_image:converting a matrix to a raster image]. In the newest version of pylab (check that your {{{pylab.matplotlib.version}}} is superior to {{{'0.98.0'}}}) you get directly a 2D numpy array if the image is grayscale.
- to write an image, do
import Image mode = 'L' size= (256, 256) imNew=Image.new(mode , size) mat = numpy.random.uniform(size = size) data = numpy.ravel(mat) data = numpy.floor(data * 256)
imNew.putdata(data) imNew.save("rand.png") </code>
- this kind of functions live also under {{{scipy.misc}}}, see for instance {{{scipy.misc.imsave}}} to create a color image:
from scipy.misc import imsave import numpy a = numpy.zeros((4,4,3)) a[0,0,:] = [128, 0 , 255] imsave('graybackground_with_a_greyish_blue_square_on_top.png',a)
- to define the range, use:
from scipy.misc import toimage import numpy a = numpy.random.rand(25,50) #between 0. and 1. toimage(a, cmin=0., cmax=2.).save('low_contrast_snow.png')(adapted from http://telin.ugent.be/~slippens/drupal/scipy_unscaledimsave )
- there was another (more direct) method suggested by http://jehiah.cz/archive/creating-images-with-numpy
Section author: LaurentPerrinet