我有这个代码，它会在屏幕上生成条形码。 但它太小而无法打印。所以，我想缩放大小，但为什么$thumb图像没有显示在屏幕上？仅显示$image（原始图像）。我在这里错过了什么？谢谢
<?php
//-- bunch of codes here --
//-- then generate image --
// Draw barcode to the screen
header ('Content-type: image/png');
imagepng($image);
imagedestroy($image);
// Then resize it
// Get new sizes
list($width, $height) = getimagesize($image);
$newwidth = $width * 2;
$newheight = $height * 2;
// Resize
imagecopyresized($thumb, $image, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
// Output and free memory
header ('Content-type: image/png');
imagepng($thumb);
imagedestroy($thumb);
?>
虽然没有所有代码来处理我模拟的部分 - 最终结果是一个新图像，其大小是原始图像的两倍。最主要的是最初不发送标头，而是将生成的图像保存到临时文件中，然后使用它。
<?php
//-- bunch of codes here --
//-- then generate image --
/* You will already have a resource $image, this emulates that $image so you do not need this line */
$image=imagecreatefrompng( 'c:/wwwroot/images/maintenance.png' );
/* define name for temp file */
$tmpimgpath=tempnam( sys_get_temp_dir(), 'img' );
/* do not send headers here but save as a temp file */
imagepng( $image, $tmpimgpath );
// Then resize it, Get new sizes ( using the temp file )
list( $width, $height ) = getimagesize( $tmpimgpath );
$newwidth = $width * 2;
$newheight = $height * 2;
/* If $thumb is defined outwith the code you posted then you do not need this line either */
$thumb=imagecreatetruecolor( $newwidth, $newheight );
// Resize
imagecopyresized( $thumb, $image, 0, 0, 0, 0, $newwidth, $newheight, $width, $height );
// Output and free memory
header ('Content-type: image/png');
@imagedestroy( $image );
@imagepng( $thumb );
@imagedestroy( $thumb );
@unlink( $tmpimgpath );
?>