PHP 对png 图像进行缩放，支持透明背景

function smart_resize_image( $file, $width = 0, $height = 0, $proportional = false, $output = 'file', $delete_original = true, $use_linux_commands = false )

{

if ( $height <= 0 && $width <= 0 ) {

return false;

}

$info = getimagesize($file);

$image = '';

$final_width = 0;

$final_height = 0;

list($width_old, $height_old) = $info;

if ($proportional) {

if ($width == 0) $factor = $height/$height_old;

elseif ($height == 0) $factor = $width/$width_old;

else $factor = min ( $width / $width_old, $height / $height_old);

$final_width = round ($width_old * $factor);

$final_height = round ($height_old * $factor);

}

else {

$final_width = ( $width <= 0 ) ? $width_old : $width;

$final_height = ( $height <= 0 ) ? $height_old : $height;

}

switch ($info[2] ) {

case IMAGETYPE_GIF:

$image = imagecreatefromgif($file);

break;

case IMAGETYPE_JPEG:

$image = imagecreatefromjpeg($file);

break;

case IMAGETYPE_PNG:

$image = imagecreatefrompng($file);

break;

default:

return false;

}

$image_resized = imagecreatetruecolor( $final_width, $final_height );

if ( ($info[2] == IMAGETYPE_GIF) || ($info[2] == IMAGETYPE_PNG) ) {

$trnprt_indx = imagecolortransparent($image);

// If we have a specific transparent color

if ($trnprt_indx >= 0) {

// Get the original image's transparent color's RGB values

$trnprt_color = imagecolorsforindex($image, $trnprt_indx);

// Allocate the same color in the new image resource

$trnprt_indx = imagecolorallocate($image_resized, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);

// Completely fill the background of the new image with allocated color.

imagefill($image_resized, 0, 0, $trnprt_indx);

// Set the background color for new image to transparent

imagecolortransparent($image_resized, $trnprt_indx);

}

// Always make a transparent background color for PNGs that don't have one allocated already

elseif ($info[2] == IMAGETYPE_PNG) {

// Turn off transparency blending (temporarily)

imagealphablending($image_resized, false);

// Create a new transparent color for image

$color = imagecolorallocatealpha($image_resized, 0, 0, 0, 127);

// Completely fill the background of the new image with allocated color.

imagefill($image_resized, 0, 0, $color);

// Restore transparency blending

imagesavealpha($image_resized, true);

}

}

imagecopyresampled($image_resized, $image, 0, 0, 0, 0, $final_width, $final_height, $width_old, $height_old);

if ( $delete_original ) {

if ( $use_linux_commands )

exec('rm '.$file);

else

@unlink($file);

}

switch ( strtolower($output) ) {

case 'browser':

$mime = image_type_to_mime_type($info[2]);

header("Content-type: $mime");

$output = NULL;

break;

case 'file':

$output = $file;

break;

case 'return':

return $image_resized;

break;

default:

break;

}

switch ($info[2] ) {

case IMAGETYPE_GIF:

imagegif($image_resized, $output);

break;

case IMAGETYPE_JPEG:

imagejpeg($image_resized, $output);

break;

case IMAGETYPE_PNG:

imagepng($image_resized, $output);

break;

default:

return false;

}

return true;

}