Question

什么可能导致php gd在调整大小后产生黑色图像？以下代码始终为每个有效的jpeg文件输出黑色图像。

<?php

$filename = 'test.jpg';
$percent = 0.5;

header('Content-Type: image/jpeg');

list($width, $height) = getimagesize($filename);
$newwidth = $width * $percent;
$newheight = $height * $percent;

$thumb = imagecreatetruecolor($newwidth, $newheight);
$source = imagecreatefromjpeg($filename);

imagecopyresized($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

imagejpeg($thumb);
imagedestroy($thumb);
?>

gd_info()的输出：

  Array
(
    [GD Version] => bundled (2.1.0 compatible)
    [FreeType Support] => 1
    [FreeType Linkage] => with freetype
    [T1Lib Support] => 
    [GIF Read Support] => 1
    [GIF Create Support] => 1
    [JPEG Support] => 1
    [PNG Support] => 1
    [WBMP Support] => 1
    [XPM Support] => 
    [XBM Support] => 1
    [JIS-mapped Japanese Font Support] => 
)

代码似乎在其他环境中工作。可能它与操作系统，已安装的软件包，库等有关吗？

Answer 1

研究

试图重现你的情况。使用开箱即用的PHP和Apache运行代码将显示以下内容

图片“http://localhost/”无法显示，因为它包含错误。

虽然浏览器告诉您存在一些错误，但由于响应中返回的标头为Content-Type: image/jpeg而无法看到，因此强制浏览器将其解释为图像。删除header并设置以下内容将输出错误。

ini_set('error_reporting', E_ALL);
ini_set('display_errors', true);
...
//header('Content-Type: image/jpeg');
...

回答

调整大小后会导致php gd产生黑色图像的原因是什么？

由于gd_info输出证明加载了GD extension，请检查文件名（linux是caseSensitive）和权限是否正确。如果Apache正在www-data（组）

运行

sudo chown :www-data test.jpg && sudo chmod 660 test.jpg

代码改进/解决方案

ini_set('error_reporting', E_ALL);
ini_set('display_errors', true);

if (extension_loaded('gd') && function_exists('gd_info'))
{
    $filename = 'test.jpg';

    if (file_exists($filename) && is_readable($filename))
    {
        $percent = 0.5;

        header('Content-Type: image/jpeg');

        list($width, $height) = getimagesize($filename);
        $newwidth = $width * $percent;
        $newheight = $height * $percent;

        $thumb = imagecreatetruecolor($newwidth, $newheight);
        $source = imagecreatefromjpeg($filename);

        imagecopyresized($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

        imagejpeg($thumb);
        imagedestroy($thumb);
    }
    else
    {
        trigger_error('File or permission problems');
    }
}
else
{
    trigger_error('GD extension not loaded');
}

这应该用作临时解决方案（开发环境）。恕我直言，错误应由中央错误处理程序处理，生成中display_errors应为false。此外，默认情况下会记录错误（在这种情况下会有Fatal error） - 检查日志以获取更多（频繁，更好）。此外，在linux上（使用apt），单行将在您的系统上安装GD：

sudo apt-get update && sudo apt-get install php5-gd && sudo /etc/init.d/apache2 restart

Answer 2

确保已安装并启用gd。

要检查，请使用以下命令创建PHP文件：

<?php phpinfo();

通过浏览器访问该文件，然后向下滚动到gd部分。如果gd不存在，或者它被禁用，请使用yum，apt-get或Windows等效项添加它。

您还需要GD库（http://www.libgd.org/）。

考虑切换到IMagick（http://php.net/manual/en/book.imagick.php）以获得更好的图像质量。

Answer 3

尝试使用此代码查看正在发生的错误：

<?php
error_reporting(E_ALL);
ini_set("display_errors", 1);

$filename = 'test.jpg';
$percent = 0.5;

list($width, $height) = getimagesize($filename);
$newwidth = $width * $percent;
$newheight = $height * $percent;

$thumb = imagecreatetruecolor($newwidth, $newheight);
$source = imagecreatefromjpeg($filename);

imagecopyresized($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

//header('Content-Type: image/jpeg');
//imagejpeg($thumb);
//imagedestroy($thumb);
?>

因此，如果PHP遇到错误，它将在屏幕上显示。如果没有错误，屏幕将显示空白。

Answer 4

下面的功能会创建一个缩略图，只需很少的更改，您也可以将其O / P添加到屏幕上。我认为这样更有用。

/*
 * PHP function to resize an image maintaining aspect ratio
 * http://salman-w.blogspot.com/2008/10/resize-images-using-phpgd-library.html
 *
 * Creates a resized (e.g. thumbnail, small, medium, large)
 * version of an image file and saves it as another file
 */

define('THUMBNAIL_IMAGE_MAX_WIDTH', 150);
define('THUMBNAIL_IMAGE_MAX_HEIGHT', 150);

function generate_image_thumbnail($source_image_path, $thumbnail_image_path)
{
    list($source_image_width, $source_image_height, $source_image_type) = getimagesize($source_image_path);
    switch ($source_image_type) {
        case IMAGETYPE_GIF:
            $source_gd_image = imagecreatefromgif($source_image_path);
            break;
        case IMAGETYPE_JPEG:
            $source_gd_image = imagecreatefromjpeg($source_image_path);
            break;
        case IMAGETYPE_PNG:
            $source_gd_image = imagecreatefrompng($source_image_path);
            break;
    }
    if ($source_gd_image === false) {
        return false;
    }
    $source_aspect_ratio = $source_image_width / $source_image_height;
    $thumbnail_aspect_ratio = THUMBNAIL_IMAGE_MAX_WIDTH / THUMBNAIL_IMAGE_MAX_HEIGHT;
    if ($source_image_width <= THUMBNAIL_IMAGE_MAX_WIDTH && $source_image_height <= THUMBNAIL_IMAGE_MAX_HEIGHT) {
        $thumbnail_image_width = $source_image_width;
        $thumbnail_image_height = $source_image_height;
    } elseif ($thumbnail_aspect_ratio > $source_aspect_ratio) {
        $thumbnail_image_width = (int) (THUMBNAIL_IMAGE_MAX_HEIGHT * $source_aspect_ratio);
        $thumbnail_image_height = THUMBNAIL_IMAGE_MAX_HEIGHT;
    } else {
        $thumbnail_image_width = THUMBNAIL_IMAGE_MAX_WIDTH;
        $thumbnail_image_height = (int) (THUMBNAIL_IMAGE_MAX_WIDTH / $source_aspect_ratio);
    }
    $thumbnail_gd_image = imagecreatetruecolor($thumbnail_image_width, $thumbnail_image_height);
    imagecopyresampled($thumbnail_gd_image, $source_gd_image, 0, 0, 0, 0, $thumbnail_image_width, $thumbnail_image_height, $source_image_width, $source_image_height);
    imagejpeg($thumbnail_gd_image, $thumbnail_image_path, 90);
    imagedestroy($source_gd_image);
    imagedestroy($thumbnail_gd_image);
    return true;
}

参考this more信息。

如果php-gd不存在，请使用以下命令。

sudo apt-get install php5-gd

使用GD调整大小输出黑色图像

4 个答案: