图像压缩增加了PHP中的文件大小

Question

我刚刚编写了PHP代码来压缩图像大小。我的代码压缩图像，但不是所有的时间。在10％的情况下，它会增加图像尺寸。请说出为什么会发生这种情况？这里是我的代码（在这里两个功能，一是为PNG图像等的JPG图片）

function compressImageSmall($source_url, $destination_url, $quality) { 
    //$quality :: 0 - 100 
    $info = getimagesize($source_url); 

    if ($info['mime'] == 'image/jpeg') 
    { 
     $image = imagecreatefromjpeg($source_url); 
     //save file 
     imagejpeg($image, $destination_url, $quality);//ranges from 0 (worst quality, smaller file) to 100 (best quality, biggest file). The default is the default IJG quality value (about 75). 
     //Free up memory 
     imagedestroy($image); 
    } 
    elseif ($info['mime'] == 'image/png') 
    { 
     $image = imagecreatefrompng($source_url); 

     //imagepng($image); 

     imageAlphaBlending($image, true); 
     imageSaveAlpha($image, true); 

     /* chang to png qulity*/ 
     $png_quality = 9 - (($quality * 9)/100); 
     imagePng($image, $destination_url, $png_quality);//Compression level: from 0 (no compression) to 9. 
     //Free up memory 
     imagedestroy($image); 

    } 

    //return destination file 
    return $destination_url; 
} 


function compressImage($source_url, $destination_url, $quality) { 
    $info = getimagesize($source_url); 

    if ($info['mime'] == 'image/jpeg') $image = imagecreatefromjpeg($source_url); 
    elseif ($info['mime'] == 'image/gif') $image = imagecreatefromgif($source_url); 
    elseif ($info['mime'] == 'image/png') $image = imagecreatefrompng($source_url); 

    //save it 
    //echo '<pre>';print_r(imagejpeg($image));// 
    imagejpeg($image, $destination_url, $quality); 

    //return destination file url 
    return $destination_url; 
} 

Answer 1

腓建于像imagejpeg功能，imagepngImage都得心应手压缩图像。以下是图像压缩的完整代码示例：How to compress image file while uploading - PHP example ...