使用 PHP 创建一个透明的 png 文件

Create a transparent png file using PHP

提问by user782104

Currently I would like to create a transparent png with the lowest quality .

目前我想创建一个质量最低的透明 png。

The code:

编码：

<?php
function createImg ($src, $dst, $width, $height, $quality) {
    $newImage = imagecreatetruecolor($width,$height);
    $source = imagecreatefrompng($src); //imagecreatefrompng() returns an image identifier representing the image obtained from the given filename.
    imagecopyresampled($newImage,$source,0,0,0,0,$width,$height,$width,$height);
    imagepng($newImage,$dst,$quality);      //imagepng() creates a PNG file from the given image. 
    return $dst;
}

createImg ('test.png','test.png','1920','1080','1');
?>

However, there are some problems:

但是，存在一些问题：

1. Do I need to specific a png file before creating any new file? Or can I create without any existing png file?

   Warning: imagecreatefrompng(test.png): failed to open stream: No such file or directory in

   C:\DSPadmin\DEV\ajax_optipng1.5\create.php on line 4

2. Although there are error message , it still generate a png file , however, what I found that is the file is a black color image , do I need to specific any parameter to make it transparent?

1. 在创建任何新文件之前，我是否需要指定一个 png 文件？或者我可以在没有任何现有 png 文件的情况下创建吗？

   警告：imagecreatefrompng(test.png)：无法打开流：中没有这样的文件或目录

   C:\DSPadmin\DEV\ajax_optipng1.5\create.php 第 4 行

2. 虽然有报错信息，但还是生成了一个png文件，但是，我发现文件是黑色图像，是否需要指定任何参数使其透明？

Thanks.

谢谢。

回答by max-m

To 1) imagecreatefrompng('test.png')tries to open the file test.pngwhich then can be edited with GD functions.

To 1) imagecreatefrompng('test.png')尝试打开文件test.png，然后可以使用 GD 功能进行编辑。

To 2) To enable saving of the alpha channel imagesavealpha($img, true);is used. The following code creates a 200x200px sized transparent image by enabling alpha saving and filling it with transparency.

到 2) 启用 alpha 通道的保存imagesavealpha($img, true);被使用。下面的代码通过启用 alpha 保存并用透明度填充它来创建一个 200x200px 大小的透明图像。

<?php
$img = imagecreatetruecolor(200, 200);
imagesavealpha($img, true);
$color = imagecolorallocatealpha($img, 0, 0, 0, 127);
imagefill($img, 0, 0, $color);
imagepng($img, 'test.png');

回答by neuraminidase7

Take a look at:

看一眼：

• imagecolorallocatealpha
• imagefill

• 图像颜色分配alpha
• 图像填充

An example function copies transparent PNG files:

一个示例函数复制透明的 PNG 文件：

    <?php
    function copyTransparent($src, $output)
    {
        $dimensions = getimagesize($src);
        $x = $dimensions[0];
        $y = $dimensions[1];
        $im = imagecreatetruecolor($x,$y); 
        $src_ = imagecreatefrompng($src); 
        // Prepare alpha channel for transparent background
        $alpha_channel = imagecolorallocatealpha($im, 0, 0, 0, 127); 
        imagecolortransparent($im, $alpha_channel); 
        // Fill image
        imagefill($im, 0, 0, $alpha_channel); 
        // Copy from other
        imagecopy($im,$src_, 0, 0, 0, 0, $x, $y); 
        // Save transparency
        imagesavealpha($im,true); 
        // Save PNG
        imagepng($im,$output,9); 
        imagedestroy($im); 
    }
    $png = 'test.png';

    copyTransparent($png,"png.png");
    ?>

回答by user3051471

1) You can create a new png file without any existing one. 2) You get a black color image because you use imagecreatetruecolor();. It creates a highest quality image with a black background. As you need a lowest quality image use imagecreate();

1) 您可以创建一个没有任何现有 png 文件的新 png 文件。2）你得到一个黑色图像，因为你使用imagecreatetruecolor();. 它创建具有黑色背景的最高质量图像。当您需要最低质量的图像时，请使用imagecreate();

<?php
$tt_image = imagecreate( 100, 50 ); /* width, height */
$background = imagecolorallocatealpha( $tt_image, 0, 0, 255, 127 ); /* In RGB colors- (Red, Green, Blue, Transparency ) */
header( "Content-type: image/png" );
imagepng( $tt_image );
imagecolordeallocate( $background );
imagedestroy( $tt_image );
?>

You can read more in this article: How to Create an Image Using PHP

您可以在本文中阅读更多内容：如何使用 PHP 创建图像