R help - Jan 2010 - detect brightness of hex color value in R / convert from hex to hsl/hsv space how?

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On Fri, 29 Jan 2010, Mark Heckmann wrote:
> To the R color experts:
> I need to detect if a chosen background color (as hex e.g. #910322) is
> light or dark.
> If it is dark I need to ovelay it with light text and vice versa.
You can use the "colorspace" package for that. hex2RGB() converts a
hex
string to "RGB" coordinates which in turn can be easily converted to 
systems like "HSV" or (preferably) HCL (called "polarLUV" in
colorspace).

R> as(hex2RGB("#910322"), "polarLUV")
             L        C        H
[1,] 31.61831 95.14145 6.913428

"L" corresponds to the luminance (whether a color is light or dark),
"C"
is chroma (how colorful the color is compared to a gray with the same 
luminance), and "H" is the hue.

hth,
Z
> Thus I would like to implement the following pseudo code:
>
> if (brightness(color) > somevalue) textcolor= dark else textcolor=red
>
> I am not too familiar with color systems. My idea was to convert the
> hex value to hsv / hsl space and extract the v or l value.
> 1) I am not sure if this is the way to go.
> 2) I do not succeed in it. convertColor {grDevices} or make.rgb
> {grDevices} did not help me with that. How can I convert hex to hsv/
> hsl space
>
> How would you detect the (perceived) color brightness?
>
> Thanks
> Mark
>
> ???????????????????????????????????????
> Mark Heckmann
> Dipl. Wirt.-Ing. cand. Psych.
> Vorstra?e 93 B01
> 28359 Bremen
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
>
>
>
>
>
> 	[[alternative HTML version deleted]]
>
>

Perhaps some variation of

   SetTextContrastColor <- function(color)
   {
     ifelse( mean(col2rgb(color)) > 127, "black",
"white")
   }

Mark Heckmann wrote:
> To the R color experts:
> I need to detect if a chosen background color (as hex e.g. #910322) is  
> light or dark.
> If it is dark I need to ovelay it with light text and vice versa.
> 
> Thus I would like to implement the following pseudo code:
> 
> if (brightness(color) > somevalue) textcolor= dark else textcolor=red
> 
> I am not too familiar with color systems. My idea was to convert the  
> hex value to hsv / hsl space and extract the v or l value.
> 1) I am not sure if this is the way to go.
> 2) I do not succeed in it. convertColor {grDevices} or make.rgb  
> {grDevices} did not help me with that. How can I convert hex to hsv/ 
> hsl space
> 
> How would you detect the (perceived) color brightness?
> 
> Thanks
> Mark
> 
> ???????????????????????????????????????
> Mark Heckmann
> Dipl. Wirt.-Ing. cand. Psych.
> Vorstra?e 93 B01
> 28359 Bremen
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
> 
> 
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
> 

-- 
Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA

There is a col2grey (and col2gray) function in the TeachingDemos package that
use a common algorithm to convert colors to grey based on perceived lightness,
that may work for you on deciding the color.

For placing text on colored backgrounds, look at the shadowtext function (also
in TeachingDemos) for another way.

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Mark Heckmann
> Sent: Friday, January 29, 2010 3:09 AM
> To: r-help at r-project.org
> Subject: [R] detect brightness of hex color value in R / convert from
> hex to hsl/hsv space how?
> 
> To the R color experts:
> I need to detect if a chosen background color (as hex e.g. #910322) is
> light or dark.
> If it is dark I need to ovelay it with light text and vice versa.
> 
> Thus I would like to implement the following pseudo code:
> 
> if (brightness(color) > somevalue) textcolor= dark else textcolor=red
> 
> I am not too familiar with color systems. My idea was to convert the
> hex value to hsv / hsl space and extract the v or l value.
> 1) I am not sure if this is the way to go.
> 2) I do not succeed in it. convertColor {grDevices} or make.rgb
> {grDevices} did not help me with that. How can I convert hex to hsv/
> hsl space
> 
> How would you detect the (perceived) color brightness?
> 
> Thanks
> Mark
> 
> ---------------------------------------
> Mark Heckmann
> Dipl. Wirt.-Ing. cand. Psych.
> Vorstra?e 93 B01
> 28359 Bremen
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
> 
> 
> 
> 
> 
> 	[[alternative HTML version deleted]]