Check if UIColor is dark or bright?

Question

I need to determine whether a selected UIColor (picked by the user) is dark or bright, so I can change the color of a line of text that sits on top of that color, for better readability.

Here's an example in Flash/Actionscript (with demo): http://web.archive.org/web/20100102024448/http://theflashblog.com/?p=173

Any thoughts?

Cheers, Andre

UPDATE

Thanks to everyone's suggestions, here's the working code:

- (void) updateColor:(UIColor *) newColor
{
    const CGFloat *componentColors = CGColorGetComponents(newColor.CGColor);

    CGFloat colorBrightness = ((componentColors[0] * 299) + (componentColors[1] * 587) + (componentColors[2] * 114)) / 1000;
    if (colorBrightness < 0.5)
    {
        NSLog(@"my color is dark");
    }
    else
    {
        NSLog(@"my color is light");
    }
}

Thanks once again :)

Answer 1

W3C has the following: http://www.w3.org/WAI/ER/WD-AERT/#color-contrast

If you're only doing black or white text, use the color brightness calculation above. If it is below 125, use white text. If it is 125 or above, use black text.

edit 1: bias towards black text. :)

edit 2: The formula to use is ((Red value * 299) + (Green value * 587) + (Blue value * 114)) / 1000.