Brightness of color can be found in quite easy way.
If we have decimal representation of RGB brightness in percents will be
100*(((R+G+B)/3)/255)
Color brightness represents position of particular color in color tween from
0xFFFFFF at 0 position The base color at position 127.5 and 0x0 at 255.
2006/7/30, Bernard Poulin <[EMAIL PROTECTED]>:
hum, I guess you missed my last post(?)
Here's the code again:
function computeBrightness(pixelvalue)
{
var r = pixelvalue >> 16 & 0xFF;
var g = pixelvalue >> 8 & 0xFF;
var b = pixelvalue & 0xFF;
var bright = Math.max(Math.max(r,g),b);
return Math.round((bright/255)*100);
}
And for an "optimized/faster" version, you could try something like:
function computeBrightness(pixelvalue)
{
// returns the larger value of r, g or b -- and scale it down to a
0..100
range.
var r = pixelvalue >> 16 & 0xFF;
var g = pixelvalue >> 8 & 0xFF;
var b = pixelvalue & 0xFF;
var bright = (r>g)?((r>b)?r:b):((g>b)?g:b);
return (bright/255)*100; // no rounding.
}
(Again, this is untested code -- but it looks like it should work).
Bernard
2006/7/30, James Deakin <[EMAIL PROTECTED]>:
>
> HI Guys, Thanks very much to you all for your help and explanations. I
> understood that the number represented a colour value but I now have a
> much better understanding of how it does so.
>
> In your opinion what is the most efficient way to retrieve the
> relative brightness of that colour.
>
> What I need is a value between 0 and 100 where 0 is black and 100 is
> white and the numbers in-between represent the shades in-between.
>
> What I am going to try is this.
>
> Split the number into its components RGB
>
> use this code which came from the Flash API project
>
> //colorModel converter RGB->HSB
> //returns a hsb object
> RGBtoHSB = function(rgb){
> var r = rgb.r
> var g = rgb.g
> var b = rgb.b
> var hsb = new Object();
> hsb.b = Math.max(Math.max(r,g),b);
> var min = Math.min(Math.min(r,g),b);
> hsb.s = (hsb.b <= 0) ? 0 : Math.round (100*(hsb.b - min)/hsb.b);
> hsb.b = Math.round((hsb.b /255)*100);
> hsb.h = 0;
> if((r == g) && (g == b)){
> hsb.h = 0;
> } else if(r >= g && g >= b){
> hsb.h = 60*(g-b)/(r-b);
> } else if(g >= r && r >= b){
> hsb.h = 60 + 60*(g-r)/(g-b);
> } else if(g >= b && b >= r){
> hsb.h = 120 + 60*(b-r)/(g-r);
> } else if(b >= g && g >= r){
> hsb.h = 180 + 60*(b-g)/(b-r);
> } else if(b >= r && r >= g){
> hsb.h = 240 + 60*(r-g)/(b-g);
> } else if(r >= b && b >= g){
> hsb.h = 300 + 60*(r-b)/(r-g);
> } else{
> hsb.h = 0;
> }
> hsb.h = Math.round(hsb.h);
> return hsb;
> }
>
> to turn it into an object with three values hue saturation and
> brightness and then just make use of the brightness.
>
> If there is a better way especially a more efficient way I would
> really like to know.
>
> On 7/29/06, Mike <[EMAIL PROTECTED]> wrote:
> > Small correction.
> >
> > This:
> > "This compares each bit in the first number to each bit in the
> > second
> > number. If both bits are 1 (on), that bit is 1 (on) in the result. If
> > both bits are 0 (off), both bits are 0 (off) in the result. So the
> > result is:"
> >
> > ...should be:
> > "This compares each bit in the first number to each bit in the
> > second
> > number. If both bits are 1 (on), that bit is 1 (on) in the result. If
> > *either bit is* 0 (off), *that bit is* 0 (off) in the result. So the
> > result is:"
> > (emphasis added)
> > --
> > T. Michael Keesey
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED]
> > [mailto:[EMAIL PROTECTED] On Behalf Of Mike
> > Sent: Saturday, July 29, 2006 3:25 PM
> > To: 'Flashcoders mailing list'
> > Subject: RE: [Flashcoders] Problems getting the brightness of a
> > colorreturnedfrom getPixel
> >
> > You seem to be thinking of numbers as if they are stored like strings.
> > They aren't.
> >
> > RGB colors are stored as 3-byte (24-bit) numbers.
> >
> > For example, red looks like this in binary:
> >
> > 111111110000000000000000b
> >
> > ...which is the same thing as this in hexadecimal:
> >
> > 0xFF0000
> >
> > ... which is the same thing as this in decimal:
> >
> > 16711680
> >
> > To isolate, for example the red portion, you can use SHIFT RIGHT (>>)
to
> > shift all bits to the "right" by 16 bits. Binary:
> >
> > 111111110000000000000000b >> 16 = 11111111b
> >
> > Hexadecimal:
> >
> > 0xFF0000 >> 16 = 0xFF
> >
> > Decimal:
> >
> > 16711680 >> 16 = 255
> >
> > Generally it's a good idea not to presume that there may not be more
> > bits to the left, so you can filter them out using a bitwise AND (&).
To
> > explain, this better, here's how to extract the green value from
bright
> > cyan (0xFFFF7F):
> >
> > The binary value of the color:
> >
> > 111111111111111101111111
> >
> > Split into colors:
> >
> > 11111111 11111111 01111111
> >
> > Shift right 8 bits:
> >
> > 1111111111111111101111111b >> 8 = 1111111111111111
> >
> > In hexadecimal, this result is:
> >
> > 0xFFFF
> >
> > In decimal, it is:
> >
> > 65535
> >
> > Clearly this is too large, because it includes the red value. To
remove
> > it, we use a bitwise AND.
> >
> > 1111111111111111b & 0xFF = 11111111b = 0xFF
> >
> > To illustrate, we are taking this value:
> >
> > 1111111111111111b (=0xFFFF; =65535)
> >
> > ...and doing a bitwise AND with this value:
> >
> > 0000000011111111b (=0x00FF; =255)
> >
> > This compares each bit in the first number to each bit in the second
> > number. If both bits are 1 (on), that bit is 1 (on) in the result. If
> > both bits are 0 (off), both bits are 0 (off) in the result. So the
> > result is:
> >
> > 0000000011111111b (=0xFF; =255)
> >
> > ...which is, indeed, the green value of the color.
> >
> > So Martin Wood's example (slightly edited):
> >
> > var r:Number = color >> 16 & 0xFF;
> > var g:Number = color >> 8 & 0xFF;
> > var b:Number = color & 0xFF;
> >
> > ... is how to retrieve the red, green, and blue values from a single
RGB
> > color number.
> > --
> > T. Michael Keesey
> >
> >
> > _______________________________________________
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