calculate a colour gradient

[Mark Light]

Hi,
I have a tk.scale bar for which I want the background to change from
blue to red as I slide along it. The mechanics of this I can do, but
the colour gradient I have is very crude - basically the amount of R in
RGB just increases whilst the G and B are fixed values. Whilst this is
not really a python question does anybody have any suggestions about
calculating the RGB values for a smooth colour gradient?
Mark.

[Grégoire Dooms]

Mark Light wrote:

Hi,
I have a tk.scale bar for which I want the background to change from
blue to red as I slide along it. The mechanics of this I can do, but
the colour gradient I have is very crude - basically the amount of R in
RGB just increases whilst the G and B are fixed values. Whilst this is
not really a python question does anybody have any suggestions about
calculating the RGB values for a smooth colour gradient?

Have a look at the HSV color space and HSV -> RGB conversion:
http://en.wikipedia.org/wiki/HSV_color_space

Then linearly adjust the H while you slide the bar.

HTH,
--
Grégoire Dooms

[Paul McGuire]

"Mark Light" <li***@soton.ac.uk> wrote in message
news:ca**********@aspen.sucs.soton.ac.uk...

Hi,
I have a tk.scale bar for which I want the background to change from
blue to red as I slide along it. The mechanics of this I can do, but
the colour gradient I have is very crude - basically the amount of R in
RGB just increases whilst the G and B are fixed values. Whilst this is
not really a python question does anybody have any suggestions about
calculating the RGB values for a smooth colour gradient?
Mark.

What about:
scale R from 255 to 0
scale B from 0 to 255 (or compute as 255-R)
hold G constant (try values like 0, 64, and 128 to brighten or darken the
resulting reds and blues)

-- Paul

[Max M]

Paul McGuire wrote:

What about:
scale R from 255 to 0
scale B from 0 to 255 (or compute as 255-R)
hold G constant (try values like 0, 64, and 128 to brighten or darken the
resulting reds and blues)

Or just use the websafe colors:

http://www.lynda.com/hexpalette/images/nhue2.gif
They basically us any combination of R,G,B with the values 00,11,22...
to ...DD,EE,FF

Easy to calculate and figure out.

regards Max M

[Scott David Daniels]

Mark Light wrote:

Hi,
I have a tk.scale bar for which I want the background to change from
blue to red as I slide along it. The mechanics of this I can do, but
the colour gradient I have is very crude - basically the amount of R in
RGB just increases whilst the G and B are fixed values. Whilst this is
not really a python question does anybody have any suggestions about
calculating the RGB values for a smooth colour gradient?
Mark.

Depending on the purpose, you could: search for "color temperature"
or "black body radiation" to get a very defensible transition, or
(for false-color or some such), break the range into pieces and do
a linear interpolation inside each piece. Play with R-O-Y-G-B, for
example. Note: even intervals is not going to look right, eyeball
the boundaries.
--
-Scott David Daniels
Sc***********@Acm.Org