[SciPy-User] Matlab imfilter/fspecial equivalent

[Michael Borck]

An update.     On further testing, the problem appeared to be caused by 
converting the RGB image to grayscale, not imresize().   I was getting 
different image values using a rgb2grayscale convertor form skimage.    
If I use ndimage.imread(, flatten=True)  then I get the same values in 
the image array/matrix.     Since I was using skimage to do the 
conversion, I posted a query on the skimage  mail list, and got back the 
following response:

They're just different color conversion factors. Based on 
http://www.mathworks.com/help/images/ref/rgb2gray.html, Matlab uses:
0.2989 R + 0.5870 G + 0.1140 B

Based on the docstring for `color.rgb2gray`:
0.2125 R + 0.7154 G + 0.0721 B

So I think this will explain why the output is similar in structure but 
different in detail.  I will write a convertor using the Matlab's 
conversion factors to convince myself that the output is the same as in 
the paper.

I will post the final ported version later.

Michael.
--






On 17/05/13 8:23 AM, Brickle Macho wrote:
> I am getting closer.  Here are some observations:
>
> * If I don't imresize() the original image, then visually I can't tell 
> the difference in the output image from Matlab or Scipy.
> * Empirically the results using different kernels are the same. That 
> is the difference between two images is essentially zero.    That is 
> doesn't seem to matter if I use the imported the "fspecial()" kernel 
> from matlab;  generate my own kernel using a fgaussion(), or use 
> scipy.ndimage.gaussian_filter().
>
> So look like the problem is with ndimage.resize().
>
> Michael.
> --

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