使用 PHP 生成缩略图会导致图像质量较差

Question

$sourcePath = 'images/'; // Path of original image
$sourceUrl = '';
$sourceName = 'photo1.jpg'; // Name of original image
$thumbPath = 'thumbs/'; // Writeable thumb path
$thumbUrl = 'thumbs/';
$thumbName = "test_thumb.jpg"; // Tip: Name dynamically
$thumbWidth = 100; // Intended dimension of thumb

// Beyond this point is simply code.
$sourceImage = imagecreatefromjpeg("$sourcePath/$sourceName");
$sourceWidth = imagesx($sourceImage);
$sourceHeight = imagesy($sourceImage);

$targetImage = imagecreate($thumbWidth,$thumbWidth);
imagecopyresized($targetImage,$sourceImage,0,0,0,0,$thumbWidth,$thumbWidth,imagesx($sourceImage),imagesy($sourceImage));
imagejpeg($targetImage, "$thumbPath/$thumbName");

// By now, the thumbnail is copied into the $thumbpath
// as the file name specified in $thumbName, so display
echo "<img src='$thumbUrl$thumbName' alt=''>";

上面的代码给了我一个缩略图，这很棒，但图像质量很糟糕。 图像看起来颜色颠倒了，而且看起来像是被压扁了。 我做这个一整天都头疼。 有人有主意吗？

Answer 1

使用 imagecreatetruecolor 而不是 imagecreate 和 imagecopyresampled 而不是 imagecopyresized。

Answer 2

正如多米尼克指出的那样，第三个参数值得包括在内。 它指定 jpeg 质量。

关于“它看起来像是被压扁了”的问题，请记住，您正在从源图像制作一个方形缩略图，该缩略图本身可能是方形的，也可能不是方形的。

解决此问题的一种方法是使用源尺寸来计算出全宽或全高（取决于图像是纵向还是横向）正方形以从源复制。 这意味着用动态计算的内容替换 imagecopyresized() 参数中的“0,0,0,0”。

（编辑：示例）

function makeSquareThumb($srcImage, $destSize, $destImage = null) {
    //I'm sure there's a better way than this, but it works...
    //I don't like my folder and file checking in the middle, but need to illustrate the need for this. 

    $srcFolder = dirname($srcImage); //source folder
    $srcName = basename($srcImage); //original image filename

    //the IF ELSEIF ELSE below is NOT comprehensive - eg: what if the dest folder is the same as the source?
    //writeable nature of the destination is not checked!
    if(!destImage) {
        $destFolder = $srcFolder.'/thumbs/';
        if(!is_dir($destFolder)) {
            //make the thumbs folder if there isn't one!
            mkdir($destFolder);
        }
        $destImage = $destFolder.$srcName;
    } elseif (is_dir($destImage)) {
        $destFolder = $destImage;
        $destImage = $destFolder.'/'.$srcName;
    } else {
        $destFolder = dirname($destImage);
    }


    //Now make it!
    $srcCanvas = imagecreatefromjpeg($srcImage);
    $srcWidth = imagesx($srcCanvas);
    $srcHeight = imagesy($srcCanvas);

    //this let's us easily sample a square from the middle, regardless of apsect ratio.
    $shortSide = array($srcWidth,$srcHeight);
    sort($shortSide);

    $src_x = $srcWidth/2 - $shortSide[0]/2;
    $src_y = $srcHeight/2 - $shortSide[0]/2;

    //do it!
    $destCanvas = imagecreatetruecolor($destSize, $destSize);
    imagecopyresampled($destCanvas,$srcCanvas,0,0,$src_x,$src_y,$destSize,$destSize,$shortSide[0],$shortSide[0]);
    imagejpeg($destCanvas, $destImage);
}

Answer 3

尝试：

imagejpeg($targetImage, "$thumbPath/$thumbName", 100);