Converting a numpy array to grayscale

[Brickle Macho]

Hi tony,

Thanks.  I suspect then that ndimage.imread(, flatten=True) is using the 
older standard, hence why the image values appeared the same. For 
testing purposes, I will use Matlab's conversion factor to see if I get 
the same output as the paper.  Once I am happy it is the same, then I 
will go back to using color.rgb2gray.

Thanks for your help.


Michael.
--




On 18/05/13 1:25 AM, Tony Yu wrote:
>
>
>
> On Fri, May 17, 2013 at 12:15 PM, Brickle Macho 
> <bricklemacho at gmail.com <mailto:bricklemacho at gmail.com>> wrote:
>
>     I porting a 8 line Matlab script. 
>
>
> <snip>
>
>
>     So what is the difference between converting an array to gray
>     scale verse reading it in as grayscale?  Have I done something
>     wrong?  Is there another way to convert a numpy array to grayscale?
>
>     Any help appreciated.
>
>     Michael.
>     --
>
> Hi Michael,
>
> 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
>
> Wikipedia (http://en.wikipedia.org/wiki/Grayscale) seems to suggest 
> that Matlab's is an older standard while the one in scikit-image is a 
> more recent spec.
>
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