[scikit-image] color.lab2rgb output differs from colormine.org

[Juan Nunez-Iglesias]

Hi Michael,

Yes, it’s common in Python and you should generally work in floating point until the very final step of processing. This will help avoid accumulation of rounding errors.

See our documentation on this here:
http://scikit-image.org/docs/dev/user_guide/data_types.html

Happy coding!

Juan.

On 27 Mar 2017, 10:46 AM -0400, Michael O'Brien <mob.irl at gmail.com>, wrote:
> Using http://www.easyrgb.com/index.php
>
> CIE-L*ab   =   48.000  -14.000   25.000
>
> equals
>
> RGB 0-255  =   105.30   119.53    70.87
> RGB 0-0.1  =  0.41293  0.46875  0.27791
>
> XYZ        =   13.654   16.794    8.461
>
> Illuminant =  D65
> Observer   =  2° (1931)
>
> So Ryan was correct to say the values are scaled between 0 and 1 (I was using the wrong row in my re-conversion to 0 to 255 scale)
> This is the 1st time I've come across RGB scaled to 0 and 1. Is its common in python and does the other scikit-image functions handle the 0 -1 scaled values or should I work with 0 to 255 values to be safe?
>
>
>
>
> > On Mon, 27 Mar 2017 at 14:36 Michael O'Brien <mob.irl at gmail.com> wrote:
> > > I'm not sure what illuminant colormine uses but if you multiple by 255 you get 151,154,141 which it getting closer to what I expect (greenish colour) with 105,119,70 still being much closer
> > >
> > > On Mon, 27 Mar 2017, 14:22 Ryan Anderson, <randerson at resonon.com> wrote:
> > > > It looks to me as if lab2rgb is returning colors scaled as floats between 0 and 1 while colormine.org is returning 8 bit integers scaled 0-255.
> > > >
> > > > Try multiplying by 255 and comparing the outputs.
> > > >
> > > > On Mar 27, 2017 7:02 AM, "Michael O'Brien" <mob.irl at gmail.com> wrote:
> > > > >
> > > > >
> > > > > Hi all,
> > > > >
> > > > >
> > > > > If I use the following array of LAB values
> > > > > array([[[ 48.07851346, -14.69400135, 25.2170507 ],
> > > > > [ 63.21232753, -3.65444198, 6.67734193],
> > > > > [ 45.80027308, -2.47952304, 11.5073341 ],
> > > > > [ 46.84900559, -10.37025167, 19.92527996],
> > > > > [ 44.92476952, 19.36861848, 2.97238555],
> > > > > [ 35.50132805, 5.89086564, 1.95259827]]])
> > > > > and use the following code to pass the array to lab2rgb
> > > > > rgbcolours =color.lab2rgb(ClusterColours.values[np.newaxis])
> > > > > I get the array
> > > > > array([[[ 0.40929448, 0.47071505, 0.27701891],
> > > > > [ 0.59383913, 0.60611158, 0.55329837],
> > > > > [ 0.4393785 , 0.4276561 , 0.34999225],
> > > > > [ 0.4159481 , 0.4516056 , 0.3026519 ],
> > > > > [ 0.54449997, 0.36963636, 0.4001209 ],
> > > > > [ 0.36970012, 0.3145826 , 0.315974 ]]])
> > > > > but on colormine.org if I enter the 1st of the LAB values I get 105,119,70 for RGB and not colours so close to black
> > > > >
> > > > > Where am I going wrong?
> > > > >
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