What RGB color is this? (quick Q)

[Adam Hughes]

Thanks Stefan.  That helps clarify some of the dtypes to me; however I
still have a few confusions in regard to color data.  I should have
specified this more in my OP.

I am trying to create a program where all color data is stored as RGB.
 This requires a validator that does flexible *to_rgb()* conversion.  I
want the users to have flexibility, so it should accept names like "aqua"
as well as RGB tuples.  I realize now that imshow() will do its own
conversions, but still don't quite understand exactly what constraints I
need to impose on users for all the various use cases.  For example, if a
user enters a single integer (say 239), is there a de-facto way to
rgb-convert this?  I've tried to exhause the scenarious below; any case
with question marks is still unclear to me.

INPUT TYPE   INPUT EXAMPLE    HANDLER    DESIRED OUTPUT
-----------------------------------------------------------------------------------------------------

hex string         '#0FF000'      ColorConverter.to_rgb()    (.2, .4, .5)
name string      'purple   '      ColorConverter.to_rgb()     (.1, .8, .3)
< 1 float tuple   '    (.5, .2, .4)          PASS                   (.5,
.2, .4)
> 1 float/int tuple   (30,  28, 90)       ????                         ????
int                           140          (Digital channel?)
 (140, 140, 140)???
float                        39.5               (Error??)
???

I read on wiki that a RGB tuple with elements > 1 can be interpreted as a
"Digital Channel", so perhaps just leave these as is.  The tough cases for
me are really when a user enters a single Int or Float.  Of course, I could
just raise an exception if there's no de-facto way to handle this...


On Tue, Dec 31, 2013 at 6:15 AM, Stéfan van der Walt <stefan at sun.ac.za>wrote:

> Hi Adam
>
> On Mon, 30 Dec 2013 22:37:43 -0800, Adam Hughes wrote:
> > I noticed recently that matplotlib.colors limits RGB values to a range
> (0 -
> > 1), while in scikit image, RGB values can be much larger.  For example:
> >
> > *test = np.zeros( (500,500,3) )*
> >
> > *test[:,:,0]=50*
> > *test[:,:,1]=19*
> > *test[:,:,2]=25*
> >
> > *imshow(test); *
> >
> > Produces a teal background.  I was curious how the color teal is derived
> > from this?  I tried normalizing to 255 and and 50 but neither seemed to
> > produce the same teal color.
>
> Here's a write-up of the data-type and range representation that
> scikit-image
> uses:
>
> http://scikit-image.org/docs/0.9.x/user_guide/data_types.html
>
> When visualizing data with Matplotlib, note that data is normalized by
> default, so you have to specify "vmin" and "vmax" to correctly display your
> generated background.
>
> Regards
> Stéfan
>
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