Steve, that is a *great* catch!!! =D

On Fri, Feb 6, 2015 at 1:19 PM, Steven Silvester <steven.silvester@gmail.com> wrote:

Marcel,

When you say the output image was transparent, you mean it was all white?  I believe what happened is your call to `np.empty` creates a floating point array, which skimage expects to be in the range [0, 1], but your data is in the range [0, 255].  If you used `dtype=np.uint8` in your `np.empty` call, I suspect it would work.


Regards,

Steve


On Wednesday, February 4, 2015 at 9:22:44 AM UTC-6, Marcel Gutsche wrote:

Hi all, 

I'm not sure if it is a bug, or whether I've just overlooked something obvious, but the internet did not offer much regarding this issue. I try to get slices from an image cube which consists of several images s = 1,...,n with the same dimensions. My new slice should have the width of the original images and the height of the number of images. Here is the code to do this: 

from skimage.io import ImageCollection, imsave

from os.path import join

import numpy as np

def main(dir):

   ic = ImageCollection( join(dir, '*.png' ) )

   row = 0  

   img = np.empty((len(ic), ic[0].shape[1], ic[0].shape[2]  ) )        

   for s in range(len(ic)):    

       img[s,...] = ic[s][row,...]

#   fname = 'new_{0:03d}.jpg'.format(v) # -> wrong colors

   fname = 'new_{0:03d}.png'.format(v)  # -> output image is transparent
       imsave(fname, img)

The problem is that the output images are all transparent. My input files are .png images with an alpha channel. I have also checked the values of the alpha channel of the output which are all set to 255, which, at least to my knowledge, should set the opacity to 100%. 

Regards, 

Marcel

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