Image processing using PHP

PHP is a widely used server-side scripting language. Its powerful image processing capabilities provide very convenient tools for website developers. Using the GD (Image Processing Library) extension through PHP, you can operate on images, including scaling, cutting, rotating, adding watermarks, generating thumbnails, etc. In this article, we will learn how to use PHP for image processing.

1. Install the GD extension

Before we start using PHP for image processing, we need to make sure that the GD extension has been installed. We can check whether the GD extension has been installed by using the following command:

php -m|grep gd

If no results are found, it means that the GD extension has not been installed. Under Linux systems, we can use the following command to install:

sudo apt-get install php-gd //使用apt安装
sudo yum install php-gd //使用yum安装

Under Windows systems, we can add "extension=php_gd2.dll" to the extensions configuration in the php.ini file for installation.

2. Processing images

2.1 Open image files

In PHP, we can use the imagecreatefromjpeg() function, imagecreatefrompng() function and imagecreatefromgif() function to open the corresponding image file.

For example, we can use the following code to open a JPEG format picture named "test.jpg":

$img = imagecreatefromjpeg("test.jpg");

2.2 Adjust the image size

We can use imagecopyresampled () function to adjust the size of the image. The specific usage of this function is as follows:

bool imagecopyresampled(resource dst_image, resource src_image, int dst_x, int dst_y, int src_x, int src_y, int dst_w, int dst_h, int src_w, int src_h)

Among them, dst_image represents the target image, src_image represents the source image, dst_x and dst_y represent the starting coordinates of the copied area in the target image, src_x and src_y represent the starting coordinates of the copied area in the source image, dst_w and dst_h represent the width and height of the copied area in the target image, src_w and src_h represent the width and height of the copied area in the source image.

For example, we can resize an image to the size of 200x200:

$img = imagecreatefromjpeg("test.jpg");
$dst_img = imagecreatetruecolor(200, 200);
imagecopyresampled($dst_img, $img, 0, 0, 0, 0, 200, 200, imagesx($img), imagesy($img));

Among them, the imagecreatetruecolor() function is used to create a new true color image. The imagesx() function and imagesy() function are used to obtain the width and height of the source image respectively.

2.3 Rotate image

We can use the imagerotate() function to rotate the image. The specific usage of this function is as follows:

bool imagerotate(resource image, float angle, int bgd_color[, int ignore_transparent])

Among them, image represents the rotated image, angle Indicates the angle of rotation, bgd_color indicates the background color of the image, and ignore_transparent indicates whether to ignore transparent colors.

For example, we can rotate an image 45 degrees:

$img = imagecreatefromjpeg("test.jpg");
$dst_img = imagerotate($img, 45, 0);

2.4 Add watermark

We can use the imagecopy() function to add a watermark. The specific usage of this function As follows:

bool imagecopy(resource dst_image, resource src_image, int dst_x, int dst_y, int src_x, int src_y, int src_w, int src_h)

Among them, dst_image represents the target image, src_image represents the source image, dst_x and dst_y represent the starting coordinates of the copied area in the target image, src_x and src_y represent the starting coordinates of the copied area in the source image , src_w and src_h represent the width and height of the copied area in the source image.

For example, we can add a watermark to an image:

$img = imagecreatefromjpeg("test.jpg");
$watermark = imagecreatefrompng("watermark.png");
imagecopy($img, $watermark, imagesx($img)-imagesx($watermark)-10, imagesy($img)-imagesy($watermark)-10, 0, 0, imagesx($watermark), imagesy($watermark));

Among them, watermark.png is a watermark image in PNG format with a transparent background, which will be added to test. The lower right corner of the jpg image and 10 pixels away from the border.

2.5 Generate thumbnails

We can use the imagecopyresampled() function to generate thumbnails. The specific usage of this function is as follows:

bool imagecopyresampled(resource dst_image, resource src_image, int dst_x, int dst_y, int src_x, int src_y, int dst_w, int dst_h, int src_w, int src_h)

Among them, dst_image represents the target image, src_image Represents the source image, dst_x and dst_y represent the starting coordinates of the copied area in the target image, src_x and src_y represent the starting coordinates of the copied area in the source image, dst_w and dst_h represent the width and height of the copied area in the target image, src_w and src_h represent the width and height of the copied area in the source image.

For example, we can generate a thumbnail with a width of 100 pixels:

$img = imagecreatefromjpeg("test.jpg");
$dst_img = imagecreatetruecolor(100, imagesy($img)*(100/imagesx($img)));
imagecopyresampled($dst_img, $img, 0, 0, 0, 0, 100, imagesy($img)*(100/imagesx($img)), imagesx($img), imagesy($img));

3. Save the image file

Finally, we need to use imagejpeg( ) function, imagepng() function and imagegif() function to save the image we processed.

For example, we can use the following code to save the image we just processed to a file:

imagejpeg($dst_img, "test_thumb.jpg");

Summary

By using PHP's image processing capabilities, we can easily Implement various operations on images, including resizing, rotating, adding watermarks, generating thumbnails, etc. This is a very useful feature for developers. I hope that through the introduction of this article, readers can master the basic usage of PHP image processing and provide more convenience for their website development work.

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