How to use GD library to process images in PHP?

How to use the GD library to process images in PHP?

The GD library is a powerful image processing library. Using the GD library in PHP can implement some simple image processing functions, such as cropping, scaling, adding watermarks, etc. This article will introduce how to use the GD library to process images in PHP and give some specific code examples.

First, make sure the GD library extension is enabled on the server. You can find and uncomment "extension=gd" in the php.ini file, and then restart the server.

Next, let’s look at some common image processing operations.

1. Create thumbnails

To create thumbnails, we use the imagecopyresampled function in the GD library to scale down the original image to the specified size. The following is a sample code:

function createThumbnail($src, $dst, $width, $height) {
    $src_img = imagecreatefromjpeg($src); // 从原图像创建一个图像资源
    $dst_img = imagecreatetruecolor($width, $height); // 创建一个指定大小的新图像资源
    $src_width = imagesx($src_img); // 原图像的宽度
    $src_height = imagesy($src_img); // 原图像的高度
    $ratio = max($width / $src_width, $height / $src_height); // 计算缩放比例
    $new_width = ceil($src_width * $ratio); // 计算缩略图的宽度
    $new_height = ceil($src_height * $ratio); // 计算缩略图的高度
    $x_offset = ($new_width - $width) / 2; // 计算水平偏移量
    $y_offset = ($new_height - $height) / 2; // 计算垂直偏移量
    imagecopyresampled($dst_img, $src_img, -$x_offset, -$y_offset, 0, 0, $new_width, $new_height, $src_width, $src_height); // 缩放图像
    imagejpeg($dst_img, $dst); // 将缩略图保存到指定路径
    imagedestroy($src_img); // 销毁图像资源
    imagedestroy($dst_img);
}

// 示例使用
$source_image = 'original.jpg'; // 原图像路径
$thumbnail_image = 'thumbnail.jpg'; // 生成的缩略图路径
$thumbnail_width = 200; // 缩略图宽度
$thumbnail_height = 150; // 缩略图高度
createThumbnail($source_image, $thumbnail_image, $thumbnail_width, $thumbnail_height);

2. Add watermark

To add a watermark, we use the imagecopy function in the GD library to overlay the watermark image on the original image at the specified position. . The following is a sample code:

function addWatermark($src, $dst, $watermark) {
    $src_img = imagecreatefromjpeg($src); // 从原图像创建一个图像资源
    $watermark_img = imagecreatefrompng($watermark); // 从水印图像创建一个图像资源
    $src_width = imagesx($src_img); // 原图像的宽度
    $src_height = imagesy($src_img); // 原图像的高度
    $watermark_width = imagesx($watermark_img); // 水印图像的宽度
    $watermark_height = imagesy($watermark_img); // 水印图像的高度
    $x_offset = $src_width - $watermark_width - 10; // 水印图像的水平偏移量
    $y_offset = $src_height - $watermark_height - 10; // 水印图像的垂直偏移量
    imagecopy($src_img, $watermark_img, $x_offset, $y_offset, 0, 0, $watermark_width, $watermark_height); // 将水印图像覆盖在原图像上
    imagejpeg($src_img, $dst); // 将带有水印的图像保存到指定路径
    imagedestroy($src_img); // 销毁图像资源
    imagedestroy($watermark_img);
}

// 示例使用
$source_image = 'original.jpg'; // 原图像路径
$watermark_image = 'watermark.png'; // 水印图像路径
$watermarked_image = 'watermarked.jpg'; // 带有水印的图像路径
addWatermark($source_image, $watermarked_image, $watermark_image);

Through the above sample code, we can use the GD library to process images in PHP to generate thumbnails and add watermarks. Of course, the GD library also supports more image processing operations, such as image rotation, image border addition, etc., and can be expanded according to actual needs.

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