Thanks to all of you for your comments that has been tremedously helpful and
informative.
James
On 7/31/06, Janis Radins <[EMAIL PROTECTED]> wrote:
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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