PHP水印

Question

我正在使用此代码来创建水印。

$image = '1.jpg'; 
    $overlay = 'stamp.png'; 
    $opacity = "20"; 
    if (!file_exists($image)) { 
     die("Image does not exist."); 
    } 
    // Set offset from bottom-right corner 
    $w_offset = 0; 
    $h_offset = 100; 
    $extension = strtolower(substr($image, strrpos($image, ".") + 1)); 
    // Load image from file 
    switch ($extension) 
    { 
     case 'jpg': 
     $background = imagecreatefromjpeg($image); 
     break; 
     case 'jpeg': 
     $background = imagecreatefromjpeg($image); 
     break; 
     case 'png': 
     $background = imagecreatefrompng($image); 
     break; 
     case 'gif': 
     $background = imagecreatefromgif($image); 
     break; 
     default: 
     die("Image is of unsupported type."); 
    } 
    // Find base image size 
    $swidth = imagesx($background); 
    $sheight = imagesy($background); 
    // Turn on alpha blending 
    imagealphablending($background, true); 
    // Create overlay image 
    $overlay = imagecreatefrompng($overlay); 
    // Get the size of overlay 
    $owidth = imagesx($overlay); 
    $oheight = imagesy($overlay); 
    // Overlay watermark 
    imagecopymerge($background, $overlay, $swidth - $owidth - $w_offset, $sheight - $oheight - $h_offset, 0, 0, $owidth, $oheight, $opacity); 
    imagejpeg($background,$image); 
    // Destroy the images 
    imagedestroy($background); 
    imagedestroy($overlay); 

png图像包含一个文本，其他所有区域都是透明的。 但是当我执行这段代码时，它将png应用于jpg，但透明度并不维持png。它显示在一个盒子里。

我该如何实现这一目标。即如果一个PNG包含transaparent部分，它应该在该部分显示下面的图像....？

Answer 1

用imagecopy替换imagecopymerge解决了这个问题。这里是新代码

function watermark($image){ 
    $overlay = '../../../photos/photosets/stamp.png'; 
    $opacity = "20"; 
    if (!file_exists($image)) { 
     die("Image does not exist."); 
    } 
    // Set offset from bottom-right corner 
    $w_offset = 0; 
    $h_offset = 100; 
    $extension = strtolower(substr($image, strrpos($image, ".") + 1)); 
    // Load image from file 
    switch ($extension) 
    { 
     case 'jpg': 
     $background = imagecreatefromjpeg($image); 
     break; 
     case 'jpeg': 
     $background = imagecreatefromjpeg($image); 
     break; 
     case 'png': 
     $background = imagecreatefrompng($image); 
     break; 
     case 'gif': 
     $background = imagecreatefromgif($image); 
     break; 
     default: 
     die("Image is of unsupported type."); 
    } 
    // Find base image size 
    $swidth = imagesx($background); 
    $sheight = imagesy($background); 
    // Turn on alpha blending 
    imagealphablending($background, true); 
    // Create overlay image 
    //$overlay = imagecreatefrompng($overlay); 
    // Get the size of overlay 
    $owidth = imagesx($overlay); 
    $oheight = imagesy($overlay); 

    $photo = imagecreatefromjpeg($image); 
    $watermark = imagecreatefrompng($overlay); 
      // This is the key. Without ImageAlphaBlending on, the PNG won't render correctly. 
    imagealphablending($photo, true); 
      // Copy the watermark onto the master, $offset px from the bottom right corner. 
    $offset = 10; 
    imagecopy($photo, $watermark, imagesx($photo) - imagesx($watermark) - $offset, imagesy($photo) - imagesy($watermark) - $offset, 0, 0, imagesx($watermark), imagesy($watermark)); 
      // Output to the browser 
    header("Content-Type: image/jpeg"); 
    imagejpeg($photo,$image); 
    // Overlay watermark 
    // Destroy the images 
    imagedestroy($background); 
    imagedestroy($overlay); 
} 

Answer 2

您是否尝试过使用imagecopyresampled（）？ http://php.net/manual/en/function.imagecopyresampled.php

Answer 3

jpg格式不支持透明度，所以在概念上你必须：

• 抓住从较大的图像（以JPEG）的显示像素，并把它们放入一个缓冲
• 抢非透明像素从较小的图像（水印），并将它们移动到该缓冲区中，沿途应用alpha值

您可能想让库执行此操作。我喜欢ImageMagick，特别是因为它的内置到PHP ...这里有一个如何使用它用于此目的从PHP的例子：

// Let's read the images. 
$glasses = new Imagick(); 
if (FALSE === $glasses->readImage($dir . '/glasses.png')) 
{ 
    throw new Exception(); 
} 

$face = new Imagick(); 
if (FALSE === $face->readImage($dir . '/face.jpg')) 
{ 
    throw new Exception(); 
} 

// Let's put the glasses on (10 pixels from left, 20 pixels from top of face). 
$face->compositeImage($glasses, Imagick::COMPOSITE_DEFAULT, 10, 20); 

而且here's the link为ImageMagick的:: compositeImage PHP手册页（从上面的例子来了）。