Can I swap colors in image using GD library in PHP?

Question

I got the image like this (it\'s a graph):

_{(source: kitconet.com)}

I want to change the colours, so the white is black, the graph line is li

Answer 1

I had trouble making this solution work. The image cannot be a true color image. Convert it first with imagetruecolortopalette();

$imgname = "test.gif";
$im = imagecreatefromgif ($imgname);

imagetruecolortopalette($im,false, 255);

$index = imagecolorclosest ( $im,  255,255,255 ); // get White COlor
imagecolorset($im,$index,92,92,92); // SET NEW COLOR

$imgname = "result.gif";
imagegif($im, $imgname ); // save image as gif
imagedestroy($im);

Answer 2

I know this is late and after the fact, but I've put together a script that will do this on a slightly larger scale. Hopefully someone who comes across this post can use it. It takes an number of source images that are one-color layers (your choice). You provide it with a source color and the tint of each layer and the script returns a composite image (with full transparency) colored specifically to your provided hex code.

Check out the code below. A more detailed explanation can be found on my blog.

function hexLighter($hex, $factor = 30) {
    $new_hex = '';

    $base['R'] = hexdec($hex{0}.$hex{1});
    $base['G'] = hexdec($hex{2}.$hex{3});
    $base['B'] = hexdec($hex{4}.$hex{5});

    foreach ($base as $k => $v) {
        $amount = 255 - $v;
        $amount = $amount / 100;
        $amount = round($amount * $factor);
        $new_decimal = $v + $amount;

        $new_hex_component = dechex($new_decimal);

        $new_hex .= sprintf('%02.2s', $new_hex_component);
    }

    return $new_hex;
}

// Sanitize/Validate provided color variable
if (!isset($_GET['color']) || strlen($_GET['color']) != 6) {
    header($_SERVER['SERVER_PROTOCOL'] . ' 400 Bad Request', true, 400);

    exit(0);
}

if (file_exists( "cache/{$_GET['color']}.png" )) {
    header( 'Content-Type: image/png' );
    readfile( "cache/{$_GET['color']}.png" );

    exit(0);
}

// Desired final size of image
$n_width = 50;
$n_height = 50;

// Actual size of source images
$width = 125;
$height = 125;

$image =    imagecreatetruecolor($width, $height);
            imagesavealpha($image, true);
            imagealphablending($image, false);

$n_image =  imagecreatetruecolor($n_width, $n_height);
            imagesavealpha($n_image, true);
            imagealphablending($n_image, false);

$black = imagecolorallocate($image, 0, 0, 0);
$transparent = imagecolorallocatealpha($image, 255, 255, 255, 127);

imagefilledrectangle($image, 0, 0, $width, $height, $transparent);

$layers = array();
$layers_processed = array();

$layers[] = array( 'src' => 'layer01.gif', 'level' => 0 );  // Border
$layers[] = array( 'src' => 'layer02.gif', 'level' => 35 );     // Background
$layers[] = array( 'src' => 'layer03.gif', 'level' => 100 );    // White Quotes

foreach ($layers as $idx => $layer) {
    $img = imagecreatefromgif( $layer['src'] );
    $processed = imagecreatetruecolor($width, $height);

    imagesavealpha($processed, true);
    imagealphablending($processed, false);

    imagefilledrectangle($processed, 0, 0, $width, $height, $transparent);

    $color = hexLighter( $_GET['color'], $layer['level'] );
    $color = imagecolorallocate($image,
        hexdec( $color{0} . $color{1} ),
        hexdec( $color{2} . $color{3} ),
        hexdec( $color{4} . $color{5} )
    );

    for ($x = 0; $x < $width; $x++)
        for ($y = 0; $y < $height; $y++)
            if ($black === imagecolorat($img, $x, $y))
                imagesetpixel($processed, $x, $y, $color);

    imagecolortransparent($processed, $transparent);
    imagealphablending($processed, true);

    array_push($layers_processed, $processed);

    imagedestroy( $img );
}

foreach ($layers_processed as $processed) {
    imagecopymerge($image, $processed, 0, 0, 0, 0, $width, $height, 100);

    imagedestroy( $processed );
}

imagealphablending($image, true);

imagecopyresampled($n_image, $image, 0, 0, 0, 0, $n_width, $n_height, $width, $height);

imagealphablending($n_image, true);

header( 'Content-Type: image/png' );
imagepng( $n_image, "cache/{$_GET['color']}.png" );
imagepng( $n_image );

// Free up memory
imagedestroy( $n_image );
imagedestroy( $image );

Answer 3

I haven't tried it myself but you can look at the function imagecolorset() in the GD library It does a color fill like effect, that could help with the white background.

Answer 4

I'm not aware of any ready-made functions. But I suppose you could go trough every pixel of the image and change it's colour...

Answer 5

You could try the imagefilter function http://lv.php.net/imagefilter - but that will not give your direct access to replace one color with another, just changing the r/g/b components.

A very low level solution could be implemented using imagesetpixel http://nl2.php.net/imagesetpixel to set the new pixel values.

Answer 6

The slow but sure approach, iterating over every pixel.

function ReplaceColour($img, $r1, $g1, $b1, $r2, $g2, $b2)
{
    if(!imageistruecolor($img))
        imagepalettetotruecolor($img);
    $col1 = (($r1 & 0xFF) << 16) + (($g1 & 0xFF) << 8) + ($b1 & 0xFF);
    $col2 = (($r2 & 0xFF) << 16) + (($g2 & 0xFF) << 8) + ($b2 & 0xFF);

    $width = imagesx($img); 
    $height = imagesy($img);
    for($x=0; $x < $width; $x++)
        for($y=0; $y < $height; $y++)
        {
            $colrgb = imagecolorat($img, $x, $y);
            if($col1 !== $colrgb)
                continue; 
            imagesetpixel ($img, $x , $y , $col2);
        }   
}