使用php裁剪缩放图片，并支持png透明的图片缩放

具体代码

function smart_resize_image($file, $width = 0, $height = 0, $proportional = false, $output = 'file', $delete_original = false, $use_linux_commands = false)
{
    if ($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, $height_old);
    //是否需要删除源文件
    if ($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;
}


//首先得到图片的尺寸，然后计算比例

$feng_mian_tu = 'images/shipin_bk.png';

$feng_mian_tu_info = getimagesize($feng_mian_tu);

echo "<pre>";
print_r($feng_mian_tu_info);

/* 此处为根据图片尺寸，计算缩略图尺寸，宽高
$img_width = $feng_mian_tu_info[0];

$img_height = $feng_mian_tu_info[1];


$array = explode('.', $feng_mian_tu);
$img_ext = strtolower(array_pop($array));

$new_width = bcmul($img_width, 0.87);
$new_height = bcmul($img_height, 0.87);*/

//这是固定宽高了
$new_width = 1200;
$new_height = 640;
echo '$new_width==' . $new_width;
echo '$new_height==' . $new_height;

$thumb_img_2 = 'thumb/shipin_bk_thumb_' . $new_width . '_' . $new_height . '_2.png';

$result = smart_resize_image($feng_mian_tu, $new_width, $new_height, false, $thumb_img_2, false, false);

原图

缩略图：