//test if a Jpeg is greyscale or color
function iscolor($pic_adress){
// A Pixel is Greyscale if the r = B = G
//example: colorpixel R=250, G=140 , B=19 Greyscale Pixel R=110, G= 110, B=110
//we do a check of 10 Pixels to find out if the Picture is Greyscale
$tocheck = 10;
$iscolor=false;
$temp= getimagesize($pic_adress);
$x= $temp[0];
$y= $temp[1];
$im= imagecreatefromjpeg($pic_adress);
//now check out the Pixels
for( $i = 0 ; $i< $tocheck && !$iscolor; $i++){
// Here a Random Pixel is chosen
$color = imagecolorat($im,rand(0,$x),rand(0,$y));
//Problem color is an int
//The Hex view on the number is RRGGBB
// Here we get the blue part of the Pixel
$blue = 0x0000ff & $color;
$green = 0x00ff00 & $color;
//The Green part we have to push 8 bits to the right to get an Compareable result
$green = $green >> 8;
$red =0xff0000 & $color;
//red part needs to be pushed 16 bit
$red = $red >> 16;
// if one of the Pixels isnt Greyscale it breaks an you know this is a color picture
if( $red!= $green || $green!= $blue){
$iscolor = true;
break;
}
}
return $iscolor;
}
