Image Color Analysis (PHP)
Jun 26th, 2007 by Ben
I’m working on a project at the moment where part of the brief is to allow categories of images to be analysed for the main colours they use so we’ll end up with a colour chart for the category.
I tried to find some code I could adapt for this function, but came up short. So I wrote my own. I’m putting it here in the hope that someone else might find it useful. Sorry it’s not so elegant, but I hope the method is easy enough to follow:
/**
* This function accepts a truecolor image object and analyzes the colors.
* It works by dividing the image into x*y blocks and identifying the dominant color in each
* block. It returns these colors in an array in the format array[xPos][yPos]
* @author Ben Hindmarch
* @copyright 2007
* @version 0.2 (2007-06-26)
* @abstract Grabs the main colors from an image
* @param binary $im The image object
* @param integer $xCount The number of blocks along the x-axis (default 3)
* @param integer $yCount The number of blocks along the y-axis (default 3)
* @return array containing x and y position of color, individual decimal red, green and blue
* values as well as a hex value
*/
function analyzeImageColors($im, $xCount =3, $yCount =3) {
//get dimensions for image
$imWidth =imagesx($im);
$imHeight =imagesy($im);
//find out the dimensions of the blocks we're going to make
$blockWidth =round($imWidth/$xCount);
$blockHeight =round($imHeight/$yCount);
//now get the image colors...
for($x =0; $x<$xCount; $x++) { //cycle through the x-axis
for ($y =0; $y<$yCount; $y++) { //cycle through the y-axis
//this is the start x and y points to make the block from
$blockStartX =($x*$blockWidth);
$blockStartY =($y*$blockHeight);
//create the image we'll use for the block
$block =imagecreatetruecolor(1, 1);
//We'll put the section of the image we want to get a color for into the block
imagecopyresampled($block, $im, 0, 0, $blockStartX, $blockStartY, 1, 1, $blockWidth, $blockHeight );
//the palette is where I'll get my color from for this block
imagetruecolortopalette($block, true, 1);
//I create a variable called eyeDropper to get the color information
$eyeDropper =imagecolorat($block, 1, 1);
$palette =imagecolorsforindex($block, $eyeDropper);
$colorArray[$x][$y]['r'] =$palette['red'];
$colorArray[$x][$y]['g'] =$palette['green'];
$colorArray[$x][$y]['b'] =$palette['blue'];
//get the rgb value too
$hex =sprintf("%02X%02X%02X", $colorArray[$x][$y]['r'], $colorArray[$x][$y]['g'], $colorArray[$x][$y]['b']);
$colorArray[$x][$y]['rgbHex'] =$hex;
//destroy the block
imagedestroy($block);
}
}
//destroy the source image
imagedestroy($im);
return $colorArray;
}
?>
The function works by marking out several (3×3 as default) blocks for the image; shrinking each block down to 1×1 pixels; converts the pixel image to a colour value and finally adds the value to an array which is mapped out according to the x and y position of the block before being returned.
Examples of the code working below. The image on the left was created using CSS to display the colours in the relative location they were found on the image:
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