Converting 0-1 number to RGB blue scale (Python)

Question

I have a number between 0 and 1, and I would like to convert it into the corresponding RGB components in a blue scale. So, when the number is 0, I would like to obtain [255,255,255] (i.e. white), while if the number is 1 I would like to obtain [0,0,255] (blue).

Do you know a formula or how this can be implemented with Python? It would be nice to know also how to convert the 0-1 number to other color scales, for example green (in the sense that 0 corresponds again to [255,255,255], while 1 corresponds to [0,255,0]).

Thanks in advance for any help you can provide!

score 3 · Answer 1 · edited May 23 '17 at 10:24

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That is a strange "scale", since it goes from white to blue, rather than from black ([0, 0, 0]) to blue.

Anyway, it's just a linear interpolation:

def make_blue(alpha):
  invalpha = 1 - alpha
  scaled = int(255 * invalpha)
  return [scaled, scaled, 255]

How to extending this to other color components should be obvious.

See also this answer for the general question of blending between two colors. In your case, one of the colors is white, the other one is blue for this case, but you also wondered about red and green.

edited May 23 '17 at 10:24

Community

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answered Jan 16 '14 at 10:23

unwind

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that wont give 255, 255, 255 for alpha = 0. use abs(alpha - 1) * 255 – M4rtini Jan 16 '14 at 10:26
@M4rtini Thanks, I got tripped up by the (to me) irregular requirements. :) Fixed. – unwind Jan 16 '14 at 10:28
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and it should be 0,0, 255 for alpha = 1. So it's the two first values that should be changed, last one should be 255. – M4rtini Jan 16 '14 at 10:38
@M4rtini Gaah. Indeed. Thanks, again. – unwind Jan 16 '14 at 10:39

score 3 · Accepted Answer · answered Jan 16 '14 at 10:31

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def green(brightness):
    brightness = round(255 * brightness) # convert from 0.0-1.0 to 0-255
    return [255 - brightness, 255, 255 - brightness]

def blue(brightness):
    brightness = round(255 * brightness) # convert from 0.0-1.0 to 0-255
    return [255 - brightness, 255 - brightness, 255]

# etc., green(1.0) -> [0, 255, 0]

answered Jan 16 '14 at 10:31

Matt

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You're welcome. I just realized, that `brightness` is probably the wrong word for it. Maybe `inverted_lightness`?. – Matt Jan 16 '14 at 10:43

score 0 · Answer 3 · answered Jan 16 '14 at 10:43

Use the HSL color space to get the correct value. Define the correct color with the Hue, for blue take for example the vale '0.6'. The Saturation can be the max value of 1, and take your number to control the Lightness. 0 means black, 0.5 is the color, and 1 is white. So we only use the range of 0.5 to 1. After you have define your correct HSL color, convert it to the RGB color space. Putting it all togehter

import colorsys 
colorsys.hls_to_rgb(0.6, 1, YOURNUMBER * 0.5 + 0.5)

Converting 0-1 number to RGB blue scale (Python)

3 Answers3