How to use PHP for image processing

With the rapid development of the Internet, image processing has become more and more important. There are various ways to process images. This article will focus on how to use PHP for image processing.

PHP is a server-side scripting language originally designed for web development that can easily handle images. In PHP, there are many classes and functions that can be used to process images, such as GD, ImageMagick and other libraries. In this article, we will discuss how to use the GD library for image processing.

1. Installation of GD library

The GD library is an extension library of PHP and is used to process images. Under Windows, you can enable the GD library extension in PHP's settings file php.ini and then restart the server. Under Linux, you need to compile and install through the command line. The following are the steps to install the GD library in Linux.

1. Confirm installation of gd-devel

Enter the following command in the Linux terminal:

yum info gd-devel

Confirm whether gd-devel has been installed. If not, please use the following command to install it

yum install gd-devel

2. Download and install GD library

In Linux, you can download the GD library through the following command:

wget http://cn2.php.net/distributions/php-x.x.x.tar. gz

Decompress this compressed package, enter the decompressed directory, and enter the following command in the terminal:

./configure 
--prefix=/usr/local/php 
--with-gd 
--with-jpeg 
--with-png 
--with-freetype-dir=/usr/include/freetype2 
--with-zlib-dir=/usr/include 
--with-xpm-dir=/usr/lib 
--with-ttf

Note: x.x.x is your PHP version number, for example: 7.3 .6

3. Compile GD library

Enter the following command in the terminal:

make
make install

After the installation is complete, restart Apache or nginx and enable the GD library extension .

2. Use the GD library for image processing

After enabling the GD library extension, we can use the gd library function in PHP for image processing. The following are usage examples of some common GD library functions:

1. Create a blank image

$width = 500;
$height = 500;
$image = imagecreate($width, $height);

2. Open an image

$image = imagecreatefromjpeg("image.jpg");

You can use the imagecreatefromjpeg() function to open jpeg type pictures, and other types of pictures can use the corresponding functions.

3. Resize

$width = 200;
$height = 200;
$target_image = imagecreatetruecolor($width, $height);
imagecopyresized($target_image, $image, 0, 0, 0, 0, $width, $height, imagesx($image), imagesy($image));

You can use the imagecopyresized() function to resize the image.

4. Rotation

$angle = 45;
$rotate = imagerotate($image, $angle, 0);

You can use the imagerotate() function to rotate the image.

5. Add watermark

$font = 5; // 字体大小
$x = 100; // 水印x轴位置
$y = 100; // 水印y轴位置
$color = imagecolorallocate($image, 255, 255, 255); // 颜色
$string = "水印文字"; // 水印文字
imagestring($image, $font, $x, $y, $string, $color); // 添加文字水印
$watermark = imagecreatefrompng("watermark.png"); // 打开水印图片
$watermark_width = imagesx($watermark); // 获取水印图片宽度
$watermark_height = imagesy($watermark); // 获取水印图片高度
imagecopy($image, $watermark, $x, $y, 0, 0, $watermark_width, $watermark_height);
imagedestroy($watermark); // 关闭水印图片

Add text watermark through the imagestring() function, or add image watermark through the imagecopy() function.

6. Output image

header("Content-type: image/png"); // 输出为png格式
imagepng($image);
imagedestroy($image); // 关闭图像

You can set the output type through the header() function, and then use the imagepng() function to output the image.

3. Conclusion

By using the GD library, we can easily perform PHP image processing. This article introduces the installation of the GD library and examples of common image processing operations. In actual development, you should perform specific operations and processing as needed. Hope this article will be helpful to you.

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