Detailed steps to generate image watermark using PHP and GD library

Detailed steps to generate image watermarks using PHP and GD libraries

Introduction:
In web development, we often need to add watermarks to images to protect originality or add copyright information. This article will introduce how to use PHP and GD library to realize the function of generating image watermark.

GD library introduction:
The GD library is an open source graphics library that provides a series of functions for image processing and generation. It supports multiple image formats, such as PNG, JPEG, GIF, etc., and can be used in different operating system environments.

Step 1: Ensure that the GD library has been installed
Before using the GD library, you need to ensure that the GD library has been installed correctly. You can use the following code to verify whether the GD library has been installed:

<?php
if(extension_loaded('gd') && function_exists('gd_info')) {
    echo 'GD库已经安装';
} else {
    echo 'GD库未安装';
}
?>

If the output result is "GD library has been installed", it means that the GD library has been installed correctly; if the output result is "GD library is not installed" , you need to install the GD library through relevant commands.

Step 2: Create watermark
Before generating the image watermark, we need to prepare the watermark image. Watermark images can be in various forms such as text, icons, LOGO, etc. If the watermark is text, you can use the font function in the GD library to create it; if the watermark is an icon or LOGO, you need to prepare the corresponding image file.

You can use the following code to create a text watermark:

<?php
// 创建画布
$width = 200;  // 画布宽度
$height = 100;  // 画布高度
$im = imagecreatetruecolor($width, $height);

// 设置背景颜色
$bgColor = imagecolorallocate($im, 255, 255, 255);

// 填充背景颜色
imagefill($im, 0, 0, $bgColor);

// 设置文字颜色
$textColor = imagecolorallocate($im, 0, 0, 0);

// 设置字体
$font = 'fonts/simsun.ttc';  // 字体文件路径，这里使用了宋体作为字体

// 添加水印文字
$text = 'www.example.com';  // 水印文字内容
imagettftext($im, 12, 0, 10, 50, $textColor, $font, $text);

// 输出水印图片
header('Content-Type: image/png');
imagepng($im);

// 释放内存
imagedestroy($im);
?>

In the above code, a canvas with a specified width and height is first created, and the background color is set. Then the text color and font file path are specified, and finally the watermark text is added through the imagettftext() function.

Step 3: Merge the watermark and the original image
In order to add the watermark to the original image, you can use the following code to merge the watermark and the original image:

<?php
// 原始图片路径
$originalImage = 'path/to/original.jpg';

// 水印图片路径
$watermarkImage = 'path/to/watermark.png';

// 创建画布并加载原始图片
$im = imagecreatefromjpeg($originalImage);

// 获取原始图片的宽度和高度
$originalWidth = imagesx($im);
$originalHeight = imagesy($im);

// 创建水印图片
$watermark = imagecreatefrompng($watermarkImage);

// 获取水印图片的宽度和高度
$watermarkWidth = imagesx($watermark);
$watermarkHeight = imagesy($watermark);

// 计算水印图片的位置
$positionX = ($originalWidth - $watermarkWidth) / 2;
$positionY = ($originalHeight - $watermarkHeight) / 2;

// 合并水印和原始图片
imagecopy($im, $watermark, $positionX, $positionY, 0, 0, $watermarkWidth, $watermarkHeight);

// 输出合并后的图片
header('Content-Type: image/jpeg');
imagejpeg($im);

// 释放内存
imagedestroy($im);
?>

In the code, first specify The path of the original image and watermark image. Then create a canvas and load the original image, get the width and height of the original image. Then create the watermark image and get its width and height. By calculating the position of the watermark image, use the imagecopy() function to merge the watermark with the original image. Finally, the merged image is output through the imagejpeg() function.

Conclusion:
Through the above steps, we can use PHP and GD libraries to generate image watermarks. First, we need to make sure that the GD library has been installed correctly. Then, you can create a text watermark or prepare a watermark image. Finally, by merging the watermark and the original image, the generated image is output. In this way, the function of generating image watermarks is realized. I hope this article will be helpful to generate image watermarks using PHP and GD library.

The above is the detailed content of Detailed steps to generate image watermark using PHP and GD library. For more information, please follow other related articles on the PHP Chinese website!