php图像大小过压缩

使用下面的脚本，我将获得前端的压缩图像。它们在服务器上看起来不错，但imagesize.php似乎正在破坏最终结果。这是问题的视觉效果（忽略这张图片上的细微差异，这是我的错误对齐方式）。有什么想法吗？这是剧本

    <?php

// Get the File path for the image
$imagedir = '../../imgs';
$imagename = $_GET["file"];
$sImagePath = "$imagedir/$imagename";

// If you want exact dimensions, you
// will pass 'width' and 'height'

$iThumbnailWidth = (int)$_GET['width'];
$iThumbnailHeight = (int)$_GET['height'];

// If you want proportional thumbnails,
// you will pass 'maxw' and 'maxh'

$iMaxWidth = (int)$_GET["maxw"];
$iMaxHeight = (int)$_GET["maxh"];

// Based on the above we can tell which
// type of resizing our script must do

if ($iMaxWidth && $iMaxHeight) $sType = 'scale';
else if ($iThumbnailWidth && $iThumbnailHeight) $sType = 'exact';

// The 'scale' type will make the image
// smaller but keep the same dimensions

// The 'exact' type will make the thumbnail
// exactly the width and height you choose

// To start off, we will create a copy
// of our original image in $img

$img = NULL;

// At this point, we need to know the
// format of the image

// Based on that, we can create a new
// image using these functions:
// - imagecreatefromjpeg
// - imagecreatefrompng
// - imagecreatefromgif

//$sExtension = strtolower(end(explode('.', $sImagePath)));
$explodedImagePath =  explode('.',$sImagePath);
$sExtension = strtolower(end($explodedImagePath));
if ($sExtension == 'jpg' || $sExtension == 'jpeg') {

    $img = @imagecreatefromjpeg($sImagePath)
        or die("Cannot create new JPEG image");

} else if ($sExtension == 'png') {

    $img = @imagecreatefrompng($sImagePath)
        or die("Cannot create new PNG image");

} else if ($sExtension == 'gif') {

    $img = @imagecreatefromgif($sImagePath)
        or die("Cannot create new GIF image");

}

// If the image has been created, we may proceed
// to the next step

if ($img) {

    // We now need to decide how to resize the image

    // If we chose to scale down the image, we will
    // need to get the original image propertions

    $iOrigWidth = imagesx($img);
    $iOrigHeight = imagesy($img);

    if ($sType == 'scale') {

        // Get scale ratio

        $fScale = min($iMaxWidth/$iOrigWidth,
              $iMaxHeight/$iOrigHeight);

        // To explain how this works, say the original
        // dimensions were 200x100 and our max width
            // and height for a thumbnail is 50 pixels.
        // We would do $iMaxWidth/$iOrigWidth
        // (50/200) = 0.25
        // And $iMaxHeight/$iOrigHeight
        // (50/100) = 0.5

        // We then use the min() function
        // to find the lowest value.

        // In this case, 0.25 is the lowest so that
        // is our scale. The thumbnail must be
        // 1/4th (0.25) of the original image

        if ($fScale < 1) {

            // We must only run the code below
            // if the scale is lower than 1
            // If it isn't, this means that
            // the thumbnail we want is actually
            // bigger than the original image

            // Calculate the new height and width
            // based on the scale

            $iNewWidth = floor($fScale*$iOrigWidth);
            $iNewHeight = floor($fScale*$iOrigHeight);
            // Create a new temporary image using the
            // imagecreatetruecolor function

            $tmpimg = imagecreatetruecolor($iNewWidth,
                               $iNewHeight);

            // The function below copies the original
            // image and re-samples it into the new one
            // using the new width and height

            imagecopyresampled($tmpimg, $img, 0, 0, 0, 0,
            $iNewWidth, $iNewHeight, $iOrigWidth, $iOrigHeight);

            // Finally, we simply destroy the $img file
            // which contained our original image
            // so we can replace with the new thumbnail

            imagedestroy($img);
            $img = $tmpimg;
        }    

    } else if ($sType == "exact") {

        // Get scale ratio

        $fScale = max($iThumbnailWidth/$iOrigWidth,
              $iThumbnailHeight/$iOrigHeight);

        // This works similarly to other one but
        // rather than the lowest value, we need
        // the highest. For example, if the
        // dimensions were 200x100 and our thumbnail
        // had to be 50x50, we would calculate:
        // $iThumbnailWidth/$iOrigWidth
        // (50/200) = 0.25
        // And $iThumbnailHeight/$iOrigHeight
        // (50/100) = 0.5

        // We then use the max() function
        // to find the highest value.

        // In this case, 0.5 is the highest so that
        // is our scale. This is the first step of
        // the image manipulation. Once we scale
        // the image down to 0.5, it will have the
        // dimensions of 100x50. At this point,
        // we will need to crop the image, leaving
        // the height identical but halving
        // the width to 50

        if ($fScale < 1) {

            // Calculate the new height and width
            // based on the scale

            $iNewWidth = floor($fScale*$iOrigWidth);
            $iNewHeight = floor($fScale*$iOrigHeight);
            // Create a new temporary image using the
            // imagecreatetruecolor function

            $tmpimg = imagecreatetruecolor($iNewWidth,
                            $iNewHeight);
            $tmp2img = imagecreatetruecolor($iThumbnailWidth,
                            $iThumbnailHeight);

            // The function below copies the original
            // image and re-samples it into the new one
            // using the new width and height

            imagecopyresampled($tmpimg, $img, 0, 0, 0, 0,
            $iNewWidth, $iNewHeight, $iOrigWidth, $iOrigHeight);

            // Our $tmpimg will now have the scaled down
            // image. The next step is cropping the picture to
            // make sure it's exactly the size of the thumbnail

            // The following logic choose how the image
            // will be cropped. Using the previous example, it
            // needs to take a 50x50 block from the original
            // image and copy it over to the new thumbnail

            // Since we want to copy the exact center of the
            // scaled down image, we need to find out the x
            // axis and y axis. To do so, say the scaled down
            // image now has a width of 100px but we want it
            // to be only 50px

            // Somehow, we need to select between the 25th and
            // 75th pixel to copy the middle.

            // To find this value we do:
            // ($iNewWidth/2)-($iThumbnailWidth/2)

            // ( 100px / 2 ) - (50px / 2)
            // ( 50px ) - ( 25px )
            // = 25px

            if ($iNewWidth == $iThumbnailWidth) {

                $yAxis = ($iNewHeight/2)-
                    ($iThumbnailHeight/2);
                $xAxis = 0;

            } else if ($iNewHeight == $iThumbnailHeight)  {

                $yAxis = 0;
                $xAxis = ($iNewWidth/2)-
                    ($iThumbnailWidth/2);

            }

            // We now have to resample the new image using the
            // new dimensions are axis values.

            imagecopyresampled($tmp2img, $tmpimg, 0, 0,
                       $xAxis, $yAxis,
                       $iThumbnailWidth,
                       $iThumbnailHeight,
                       $iThumbnailWidth,
                       $iThumbnailHeight);

            imagedestroy($img);
            imagedestroy($tmpimg);
            $img = $tmp2img;
        }   

    }

    // Display the image using the header function to specify
    // the type of output our page is giving

    header("Content-type: image/jpeg");
    imagejpeg($img);

}

?>

---

看起来您自己正在破坏图像：

        imagedestroy($tmpimg);
        $img = $tmp2img;
 ... snip ...
 imagejpeg($tmpimg);

在完全使用GD图像句柄（包括通过imagejpeg输出）之前，您不能
imagedestroy（）
。一旦图像被销毁，图像将从内存中消失，句柄变量将无效。
您可以使用第三个参数将压缩级别调整为。要获得最高质量（但最大的文件大小），请使用：

质量值为90可能会在质量和文件大小之间获得合理的平衡

同样，示例中的图像类型最好保存为PNG，使用。JPEG格式最适合用于摄影图像。
它破坏了不同的图像句柄；如果他在写之前销毁了它，他就不会得到任何图像。像这样的低颜色图像作为png可能会更好。PNG具有无损压缩，而jpeg仅具有有损压缩。
imagejpeg($img, NULL, 100);