PHP GD调整大小导致工件

我有一个函数，我正在使用接受用户上传的图像，按比例缩放到最大宽度/高度为4,000px，并且还生成400px和800px缩略图。它需要能够处理透明的PNG并应用白色背景。PHP GD调整大小导致工件

我的当前代码执行所有这些操作，但是，它会添加不常见的非JPEG文件。他们是垂直的条纹，看起来像一个非常黯淡的条码，当看近处（400％缩放屏幕截图）。这种情况甚至发生在原始图片上，并且以其缩放的尺寸上传。它似乎更加流行透明的PNG，但也发生在JPEG的白色区域。 JPEG文件被保存质量80

function resize_image($file, $w, $h, $strict = false, $crop = false, $path = null, $thumbnail = false) 
{ 
    // Check for Valid Image + Calculate Ratio 
    list($width, $height) = getimagesize($file); 

    if (empty($width) || empty($height)) 
    { 
     echo json_encode(['result' => 'error', 'error' => 'file_format_invalid']); 
     http_response_code(405); 
     exit; 
    } 

    $r = $width/$height; 

    if (!$strict) 
    { 
     $w = min($w, $width); 
     $h = min($h, $height); 
    } 

    $wTa = min($w, 400); 
    $hTa = min($h, 400); 

    $wTb = min($w, 800); 
    $hTb = min($h, 800); 

    // Apply Crop Constraint 
    if ($crop) 
    { 
     if ($width > $height) 
     { 
      $width = ceil($width - ($width * abs($r - $w/$h))); 
      $widthTa = ceil($width - ($width * abs($r - $wTa/$hTa))); 
      $widthTb = ceil($width - ($width * abs($r - $wTb/$hTb))); 
     } 

     else 
     { 
      $height = ceil($height - ($height * abs($r - $w/$h))); 
      $heightTa = ceil($height - ($height * abs($r - $wTa/$hTa))); 
      $heightTb = ceil($height - ($height * abs($r - $wTa/$hTb))); 
     } 

     $newWidth = $w; 
     $newHeight = $h; 
    } 

    else 
    { 
     if ($w/$h > $r || $r < 1) 
     { 
      $newWidth = $h * $r; 
      $newWidthTa = $hTa * $r; 
      $newWidthTb = $hTb * $r; 

      $newHeight = $h; 
      $newHeightTa = $hTa; 
      $newHeightTb = $hTb; 
     } 

     else 
     { 
      $newHeight = $w/$r; 
      $newHeightTa = $wTa/$r; 
      $newHeightTb = $wTb/$r; 

      $newWidth = $w; 
      $newWidthTa = $wTa; 
      $newWidthTb = $wTb; 
     } 
    } 

    // Create, Resample + Return Image 
    $src = imagecreatefromstring(file_get_contents($file)); 
    $dst = imagecreatetruecolor($newWidth, $newHeight); 
    $fff = imagecolorallocate($dst, 255, 255, 255); 

    imagefill($dst, 0, 0, $fff); 
    imagecopyresampled($dst, $src, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height); 

    if (!is_null($path)) 
    { 
     imagejpeg($dst, $path, 80); 

     if ($thumbnail) 
     { 
      $dstThumbA = imagecreatetruecolor($newWidthTa, $newHeightTa); 
      $dstThumbB = imagecreatetruecolor($newWidthTb, $newHeightTb); 

      $fffThumbA = imagecolorallocate($dstThumbA, 255, 255, 255); 
      $fffThumbB = imagecolorallocate($dstThumbB, 255, 255, 255); 

      imagefill($dstThumbA, 0, 0, $fffThumbA); 
      imagefill($dstThumbB, 0, 0, $fffThumbB); 

      imagecopyresampled($dstThumbA, $src, 0, 0, 0, 0, $newWidthTa, $newHeightTa, $width, $height); 
      imagecopyresampled($dstThumbB, $src, 0, 0, 0, 0, $newWidthTb, $newHeightTb, $width, $height); 

      imagejpeg($dstThumbA, str_replace('.jpg', '-thumb.jpg', $path), 80); 
      imagejpeg($dstThumbB, str_replace('.jpg', '[email protected]', $path), 80); 
     } 
    } 

    return $dst; 
}

来源

2017-04-17 Cameron Sumpter

我想说的尝试使用'imagecopyresized'代替'imagecopyresampled' - 也许这也有帮助http://stackoverflow.com/questions/23200823/gd-quality-issue-with-transparent -pngs || http://stackoverflow.com/questions/23993901/imagecopyresampled-introduces-artifacts-in-transparent-png –

嗯，好的想法，'imagecopyresized'确实能够工作，没有那个伪像，尽管它引入了太多的别名来被接受。我注意到这些症状出现在Ubuntu下的PHP 7.1.3上，但在开发中的Windows下不在PHP 7.0.1上。也许配置相关？ –

我的结论是，问题是特定环境（在Ubuntu下发生在PHP 7.1.3，而不是PHP 7.0.1在Windows下）。重新安装php7.1和php7.1-gd没有效果。

最终我决定硬着头皮与ImageMagick的重写，产生的代码更加简洁块：

$magickSource = new Imagick(); 
$magickSource->readImageBlob(file_get_contents($file)); 
$magickSource = $magickSource->flattenImages(); 

$magickFull = clone $magickSource; 
$magickFull->resizeImage(min($originalWidth, $newWidth), min($originalHeight, $newHeight), Imagick::FILTER_LANCZOS, 1, true); 
$magickFull->setImageCompression(Imagick::COMPRESSION_JPEG); 
$magickFull->setImageCompressionQuality(75); 
$magickFull->stripImage(); 
$magickFull->writeImage($path); 
$magickFull->destroy(); 

if ($thumbnail) 
{ 
    $magickThumb = clone $magickSource; 
    $magickThumb->resizeImage(min($originalWidth, 400), min($originalHeight, 400), Imagick::FILTER_LANCZOS, 1, true); 
    $magickThumb->setImageCompression(Imagick::COMPRESSION_JPEG); 
    $magickThumb->setImageCompressionQuality(75); 
    $magickThumb->stripImage(); 
    $magickThumb->writeImage(str_replace('.jpg', '-thumb.jpg', $path)); 
    $magickThumb->destroy(); 
}

到setImageCompression()的呼叫，setImageCompressionQuality和stripImage()产生在合并的filesizes减少了53％。（Source）

来源

2017-04-18 07:10:10

PHP GD调整大小导致工件

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