How to output images in PHP? (Detailed explanation of the legend)

In the previous article, I brought you "How to upload files in PHP? You’ll understand after reading it! 》, which introduces you in detail how to upload files in PHP. This article will take a look at the relevant knowledge of image processing in PHP. I hope it will be helpful to everyone!

Image processing is something that is often encountered in PHP work. We encounter many scenarios where images need to be processed, such as image verification codes, image watermarks, etc. In fact, the focus of learning image processing is to learn the functions of the GD system in PHP. Image processing in PHP requires the support of the GD library, so let's first take a look at the relevant knowledge about the GD library.

GD library

The GD library can be understood as a function library for creating graphics images. The GD library actually It is written in C language and can be used in PHP. In addition to PHP, it can also be used in Perl and other languages. The GD library provides many interfaces for processing images.

GD is used in PHP The library can draw various graphics images, statistical charts, and image verification codes on the page, which can also be implemented using the GD library.

The example is as follows:

<?php
phpinfo();
?>

After input, in the output result, if the two options shown below appear, it means that the current machine supports image processing through GD:

Or you can use:

<?php
    print_r(gd_info());
?>

After input, run it. If the output result is as shown in the figure below, it also means that the current machine supports processing through GD image.

If it is not installed, you can also just change the "extension=php_gd2.dll" item in the php.ini configuration file under the Windows system The previous comment deletion method is completed.

In PHP, the operation of processing images through the GD library is generally divided into 4 basic steps:

• Create canvas

• Draw image

• Output image

• Release resources

We will complete it through these four steps Now that you know the basic operations on images, let’s take a look at how to operate them.

Create canvas

All our drawing and image processing need to be completed on a background image, which is the canvas, which can be understood as For images, we have a temporary area in memory as a canvas to store image information. Future image operations will be performed on this area, which is the canvas.

imagecreate() and imagecreatetruecolor() are used to create canvas. Their syntax format is as follows:

imagecreate(int $width, int $height)
imagecreatetruecolor(int $width, int $height)

Among them, $width It means that the width of the created canvas can also be understood as the width of the image. $height means that the height of the created canvas is also the height of the image.

Both of these two functions can be used to create a canvas, but the difference is that they can The range of colors accommodated varies.

The example is as follows:

<?php
    $img = @imagecreatetruecolor(120, 20) or die(&#39;画布创建失败！&#39;);
?>

Since a canvas is just created and there is nothing on it, the browser will not output the canvas, but it can be passed through imagesx() and imagesy( ) to get the width and height of the image:

<?php
    $img = @imagecreatetruecolor(120, 20) or die(&#39;画布创建失败！&#39;);
    echo &#39;画布的宽度为：&#39;.imagesx($img).&#39;像素&#39;;
    echo &#39;<br>画布的高度为：&#39;.imagesy($img).&#39;像素&#39;;
?>

Output result:

From this we have completed creating a canvas.

In addition to using the above two functions to create a canvas, you can also create images through files or URLs in the following ways:

• ##imagecreatefromgif() : Create a new image through a GIF file or URL

• imagecreatefromjpeg() : Create a new image through a JPEG file or UR

• imagecreatefrompng() : Create a new image through a PNG file or URL

• ##imagecreatefromwbmp()

  : Create a new image through a WBMP file or URL An image

Output imageIn the above example, we have successfully created the canvas, which is different in PHP Format images also require different functions for output. The different functions are as follows:

• imagegif()

  : Output a GIF format image to the browser or File

• imagejpeg()

  : Output a JPEG format image to the browser or file

• imagepng( )

  : Output a PNG format image to a browser or file

Their syntax format is as follows:

imagegif(resource $image[, string $filename])
imagejpeg(resource $image[, string $filename[, int $quality]])
imagepng(resource $image[, string $filename])

其中，$image为创建的一个图像资源；$filename表示为参数，用来设置文件需要保存的路径。

示例如下：

首先我在根目录中已经保存了一个名为php.png的图像文件

<?php
    header(&#39;Content-type:image/jpeg&#39;);
    $image= imagecreatefrompng(&#39;php.png&#39;);
    imagepng($image);
?>

输出结果：

通过imagecreatefrompng()函数和imagepng()成功的输出了一个格式为png的图片。

释放图像资源

通过上述示例已经成功的输出了图片，在图片的资源使用完成后，通常需要释放图像处理时所占用的内存，那应该怎样操作呢？

在PHP中我们通过imagedestroy() 函数来释放图像资源，语法格式如下：

imagedestroy(resource $image)

其中$image表示需要释放资源的图像

示例如下：

<?php
    header(&#39;Content-type:image/jpeg&#39;);
    $image= imagecreatefrompng(&#39;php.png&#39;);
    imagepng($image);
    imagedestroy($image);
?>

因为释放图像资源的操作是没有输出内容的，所以就不列出输出结果了。

推荐学习：《PHP视频教程》

The above is the detailed content of How to output images in PHP? (Detailed explanation of the legend). For more information, please follow other related articles on the PHP Chinese website!