imagecreatefrompng（）使黑色背景而不是透明？

Question

我使用PHP和GD庫製作縮略圖，但是我的代碼將png透明度轉化爲純黑色，是否有解決方案來改進我的代碼？

這是我的PHP縮略圖製造商代碼：

function cropImage($nw, $nh, $source, $stype, $dest) { 
    $size = getimagesize($source); 
    $w = $size[0]; 
     $h = $size[1]; 

     switch($stype) { 
      case 'gif': 
      $simg = imagecreatefromgif($source); 
      break; 
      case 'jpg': 
      $simg = imagecreatefromjpeg($source); 
      break; 
      case 'png': 
      $simg = imagecreatefrompng($source); 
      break; 
     } 

     $dimg = imagecreatetruecolor($nw, $nh); 
     $wm = $w/$nw; 
     $hm = $h/$nh; 
     $h_height = $nh/2; 
     $w_height = $nw/2; 

     if($w> $h) { 
      $adjusted_width = $w/$hm; 
      $half_width = $adjusted_width/2; 
      $int_width = $half_width - $w_height; 
      imagecopyresampled($dimg,$simg,-$int_width,0,0,0,$adjusted_width,$nh,$w,$h); 
     } elseif(($w <$h) || ($w == $h)) { 
      $adjusted_height = $h/$wm; 
      $half_height = $adjusted_height/2; 
      $int_height = $half_height - $h_height; 

      imagecopyresampled($dimg,$simg,0,-$int_height,0,0,$nw,$adjusted_height,$w,$h); 
     } else { 
      imagecopyresampled($dimg,$simg,0,0,0,0,$nw,$nh,$w,$h); 
     } 

     imagejpeg($dimg,$dest,100); 
} 

謝謝

Answer 1

imagecreatetruecolor（）後：

<?php 

// ... Before imagecreatetruecolor() 

$dimg = imagecreatetruecolor($width_new, $height_new); // png ?: gif 

// start changes 
switch ($stype) { 

    case 'gif': 
    case 'png': 
     // integer representation of the color black (rgb: 0,0,0) 
     $background = imagecolorallocate($dimg , 0, 0, 0); 
     // removing the black from the placeholder 
     imagecolortransparent($dimg, $background); 

    case 'png': 
     // turning off alpha blending (to ensure alpha channel information 
     // is preserved, rather than removed (blending with the rest of the 
     // image in the form of black)) 
     imagealphablending($dimg, false); 

     // turning on alpha channel information saving (to ensure the full range 
     // of transparency is preserved) 
     imagesavealpha($dimg, true); 
     break; 

    default: 
     break; 
} 
// end changes 

$wm = $w/$nw; 
$hm = $h/$nh; 

// ... 

Answer 2

有時候如果.JPG圖像有內部的小錯誤（你不能看到），所有透明像素變成黑色。試用：

ini_set('gd.jpeg_ignore_warning', 1); 

Answer 3

將rgb改爲255，它會給你透明的圖像，而不是黑色。

<?php 
switch ($stype) 
{ 
    case "png": 
     // integer representation of the color black (rgb: 0,0,0) 
     $background = imagecolorallocate($simage, 255, 255, 255); 
     // removing the black from the placeholder 
     imagecolortransparent($simage, $background); 

     // turning off alpha blending (to ensure alpha channel information is preserved, rather than removed (blending with the rest of the image in the form of black)) 
     imagealphablending($simage, false); 

     // turning on alpha channel information saving (to ensure the full range of transparency is preserved) 
     imagesavealpha($simage, true); 

     break; 
    case "gif": 
     // integer representation of the color black (rgb: 0,0,0) 
     $background = imagecolorallocate($simage, 255, 255, 255); 
     // removing the black from the placeholder 
     imagecolortransparent($simage, $background); 

     break; 
} 
?> 

Answer 4

如果正確答案的代碼不起作用試試這個：

//After imagecreatetruecolor(): 
$white = imagecolorallocate($dimg, 255, 255, 255); 
imagefill($dimg,0,0,$white); 

Answer 5

操作的順序是非常重要的。對於.gif圖像，我發現我需要先複製調整大小的圖像，然後將黑色背景分配爲透明。對於PNG，我發現下面的代碼調整大小的圖像，並保持透明背景。

也，此代碼爲我工作...

$resized_image = imagecreatetruecolor($target_width, $target_height); 
switch ($asset->a_mime_type) 
{ 
    case 'image/jpeg': 
     imagecopyresampled($resized_image, $source, 0, 0, 0, 0, $target_width, $target_height, $asset->a_image_width, $asset->a_image_height); 
     $r = imagejpeg($resized_image,$file_name); 
     break; 
    case 'image/png': 
     imagealphablending($resized_image, FALSE); 
     imagesavealpha($resized_image, TRUE); 
     imagecopyresampled($resized_image, $source, 0, 0, 0, 0, $target_width, $target_height, $asset->a_image_width, $asset->a_image_height); 
     $r = @imagepng($resized_image,$file_name); 
     break; 
    case 'image/gif': 
     imagecopyresampled($resized_image, $source, 0, 0, 0, 0, $target_width, $target_height, $asset->a_image_width, $asset->a_image_height); 
     $background = imagecolorallocate($resized_image, 0, 0, 0); 
     imagecolortransparent($resized_image, $background); 
     $r = @imagegif($resized_image,$file_name); 
     break; 
} 

Answer 6

這裏是我的總測試代碼。它爲我下面的教程

$imageFileType = pathinfo($_FILES["image"]["name"], PATHINFO_EXTENSION); 
$filename = 'test.' . $imageFileType; 
move_uploaded_file($_FILES["image"]["tmp_name"], $filename); 

$source_image = imagecreatefromjpeg($filename); 

$source_imagex = imagesx($source_image); 
$source_imagey = imagesy($source_image); 

$dest_imagex = 400; 
$dest_imagey = 600; 
$dest_image = imagecreatetruecolor($dest_imagex, $dest_imagey); 

imagecopyresampled($dest_image, $source_image, 0, 0, 0, 0, $dest_imagex, $dest_imagey, $source_imagex, $source_imagey); 

imagesavealpha($dest_image, true); 
$trans_colour = imagecolorallocatealpha($dest_image, 0, 0, 0, 127); 
imagefill($dest_image, 0, 0, $trans_colour); 

imagepng($dest_image,"test1.png",1);