php gd库实现图片大小裁剪与缩放

//图片裁剪、缩放函数
//$filepath图片路径,$percent缩放百分比
function imagepress($filepath,$percent='0.5'){
// 图片类型
header('Content-Type: image/jpeg');
// 获得新的图片大小
list($width, $height) = getimagesize($filepath);
$new_width = $width * $percent;
$new_height = $height * $percent;
// 重新取样
$image_p = imagecreatetruecolor($new_width, $new_height);
$image = imagecreatefromjpeg($filepath);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
// 输出
return imagejpeg($image_p, null, 100);
}

//$filepath图片路径,$new_width新的宽度,$new_height新的高度
function imagepress($filepath, $new_width, $new_height)
{
$source_info   = getimagesize($filepath);
$source_width  = $source_info[0];
$source_height = $source_info[1];
$source_mime   = $source_info['mime'];
$source_ratio  = $source_height / $source_width;
$target_ratio  = $new_height / $new_width;

// 源图过高
if ($source_ratio > $target_ratio)
{
$cropped_width  = $source_width;
$cropped_height = $source_width * $target_ratio;
$source_x = 0;
$source_y = ($source_height - $cropped_height) / 2;
}
// 源图过宽
elseif ($source_ratio < $target_ratio)
{
$cropped_width  = $source_height / $target_ratio;
$cropped_height = $source_height;
$source_x = ($source_width - $cropped_width) / 2;
$source_y = 0;
}
// 源图适中
else
{
$cropped_width  = $source_width;
$cropped_height = $source_height;
$source_x = 0;
$source_y = 0;
}
switch ($source_mime)
{
case 'image/gif':
$source_image = imagecreatefromgif($filepath);
break;
case 'image/jpeg':
$source_image = imagecreatefromjpeg($filepath);
break;
case 'image/png':
$source_image = imagecreatefrompng($filepath);
break;
default:
return false;
break;
}
$target_image  = imagecreatetruecolor($new_width, $new_height);
$cropped_image = imagecreatetruecolor($cropped_width, $cropped_height);
// 裁剪
imagecopy($cropped_image, $source_image, 0, 0, $source_x, $source_y, $cropped_width, $cropped_height);
// 缩放
imagecopyresampled($target_image, $cropped_image, 0, 0, 0, 0, $new_width, $new_height, $cropped_width, $cropped_height);
header('Content-Type: image/jpeg');
imagejpeg($target_image);
imagedestroy($source_image);
imagedestroy($target_image);
imagedestroy($cropped_image);
}