How to use php to modify pictures

With the continuous development of web applications, we often need to batch modify and adjust images on our website. PHP is a widely used web programming language, and it also provides many built-in functions and classes that make it easy to modify images. This article will introduce how to use PHP to modify images.

1. Image format

Before we start modifying images, we need to understand some common image formats. Common image formats include JPEG, PNG, GIF, etc. Their file extensions are .jpg, .png, and .gif respectively. When processing images, it is important to know the format of the image, as each format has its own specific processing methods and properties.

2. Create Image

In PHP, we can create a new blank image using the imagecreatetruecolor() function. syntax:

$image = imagecreatetruecolor(width, height);

The parameters width and height represent the width and height of the newly created image. This blank image can be used as a base image, which can be used to add text or other images, etc.

3. Load Image

When modifying an existing image, we need to load an existing file and modify it as needed. In PHP, we can load images in JPEG, PNG and GIF formats using the imagecreatefromjpeg(), imagecreatefrompng() and imagecreatefromgif() functions. These functions load image files into memory so we can modify them however we want.

syntax:

$image = imagecreatefromjpeg('example.jpg'); //加载一个JPEG格式的图像
$image = imagecreatefrompng('example.png'); //加载一个PNG格式的图像
$image = imagecreatefromgif('example.gif'); //加载一个GIF格式的图像

Here, we will load a JPEG format image named "example.jpg". To load images in different formats, just change the relevant function and file extension.

4. Resize Image

Resizing an image is an easy way to modify an image. We can use the imagecopyresampled function to resize the image. This function copies an image onto another image, resizing it to the specified size.

syntax:

imagecopyresampled($dst_image, $src_image, $dst_x, $dst_y, $src_x, $src_y, $dst_width, $dst_height, $src_width, $src_height);

The parameter $dst_image is the target image (that is, the new image), and $src_image is the source image (that is, the original image). $dst_x and $dst_y are the coordinates of the target image, $src_x and $src_y are the coordinates of the source image. $dst_width and $dst_height are the width and height of the target image, $src_width and $src_height are the width and height of the source image. The function will extract a portion of the source image at the specified size and copy it to the destination image.

The following is a sample code that uses the imagecopyresampled() function to scale an image:

$src_image = imagecreatefromjpeg('example.jpg'); //加载原始图像
list($width, $height) = getimagesize('example.jpg'); //获取原始图像尺寸

$scale = 0.5; // 缩放比例

$dst_image = imagecreatetruecolor($width * $scale, $height * $scale); // 创建缩小的目标图像

// 缩小原始图像
imagecopyresampled($dst_image, $src_image, 0, 0, 0, 0, $width * $scale, $height * $scale, $width, $height);

// 输出图像
header('Content-Type: image/jpeg');
imagejpeg($dst_image);
imagedestroy($src_image);
imagedestroy($dst_image);

5. Fill the image

Fill the image means to change the color of the specified color The process of adding blocks to specific areas in an image. This is typically used for adding backgrounds and color filters. In PHP, we can use the imagefill() function to fill images. This function accepts two parameters: $image and $color. The $image parameter is the image that needs to be filled, and $color is the specified color.

The following is a sample code that fills the image background color with white:

$image = imagecreatefromjpeg('example.jpg'); //加载原始图像

// 获取图像宽度和高度
list($width, $height) = getimagesize('example.jpg');

// 创建一个白色的填充
$white = imagecolorallocate($image, 255, 255, 255);

// 填充图像背景
imagefill($image, 0, 0, $white);

// 输出图像
header('Content-type: image/jpeg');
imagejpeg($image);
imagedestroy($image);

6. Add text

It is common to add text to an image needs. The built-in functions such as imagestring(), imagestringup(), imagettftext() and imagettfbbox() in PHP can easily add text to images.

The following is a sample code to add red text to an image:

$image = imagecreatefromjpeg('example.jpg'); //加载原始图像

// 创建颜色
$text_color = imagecolorallocate($image, 255, 0, 0); //红色

// 添加文本
imagestring($image, 5, 50, 50, 'Hello, world!', $text_color); //渲染文本

// 输出图像
header('Content-type: image/jpeg');
imagejpeg($image);
imagedestroy($image);

7. Save the image

Finally, we need to save the modified image to the server or local computer. In PHP, we can use the imagejpeg(), imagepng() and imagegif() functions to save images in JPEG, PNG or GIF format to a specified directory.

The following is a sample code to save the modified image in JPEG format:

$dst_image = imagecreatefromjpeg('example.jpg'); //加載原始图像
list($width, $height) = getimagesize('example.jpg'); // 获取原始图像尺寸

// 调整图像大小
imagecopyresampled($dst_image, $src_image, 0, 0, 0, 0, $width * $scale, $height * $scale, $width, $height);

// 保存图像为JPEG格式
imagejpeg($dst_image, 'example_new.jpg', 100);

// 输出图像
header('Content-type: image/jpeg');
imagejpeg($dst_image);

// 销毁图像资源
imagedestroy($src_image);
imagedestroy($dst_image);

Summary

Using built-in functions and classes in PHP can quickly and easily modify images . By mastering operations such as loading, resizing, filling, adding text, and saving images, we can easily create beautiful images. Although the corresponding technologies continue to develop and change, these basic operations are always an important part of image processing and are the basic skills we need to be familiar with.

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