php – 如何使用GD调整上传图像并将其转换为PNG

我想允许用户以各种格式(至少GIF,JPEG和PNG)上传头像类型的图像,但将其全部保存为PNG数据库BLOB.如果图像超大,像素化,我想在DB插入之前调整它们大小.

使用GD进行调整大小和PNG转换的最佳方式是什么？

编辑：可悲的是,只有GD可用在我需要使用的服务器上,没有ImageMagick.

<?PHP                                              
/*
Resizes an image and converts it to PNG returning the PNG data as a string
*/
function imagetoPng($srcFile,$maxSize = 100) {  
    list($width_orig,$height_orig,$type) = getimagesize($srcFile);        

    // Get the aspect ratio
    $ratio_orig = $width_orig / $height_orig;

    $width  = $maxSize; 
    $height = $maxSize;

    // resize to height (orig is portrait) 
    if ($ratio_orig < 1) {
        $width = $height * $ratio_orig;
    } 
    // resize to width (orig is landscape)
    else {
        $height = $width / $ratio_orig;
    }

    // Temporarily increase the memory limit to allow for larger images
    ini_set('memory_limit','32M'); 

    switch ($type) 
    {
        case IMAGETYPE_GIF: 
            $image = imagecreatefromgif($srcFile); 
            break;   
        case IMAGETYPE_JPEG:  
            $image = imagecreatefromjpeg($srcFile); 
            break;   
        case IMAGETYPE_PNG:  
            $image = imagecreatefrompng($srcFile);
            break; 
        default:
            throw new Exception('Unrecognized image type ' . $type);
    }

    // create a new blank image
    $newImage = imagecreatetruecolor($width,$height);

    // copy the old image to the new image
    imagecopyresampled($newImage,$image,$width,$height,$width_orig,$height_orig);

    // Output to a temp file
    $destFile = tempnam();
    imagepng($newImage,$destFile);  

    // Free memory                           
    imagedestroy($newImage);

    if ( is_file($destFile) ) {
        $f = fopen($destFile,'rb');   
        $data = fread($f);       
        fclose($f);

        // Remove the tempfile
        unlink($destFile);    
        return $data;
    }

    throw new Exception('Image conversion Failed.');
}