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@gmail.com mailto:bricklemacho@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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