Beginner's Guide to PHP Image Processing

PHP is a very popular server-side programming language, which is widely used for web development. In web development, image processing is a very common requirement, and it is also very simple to implement image processing in PHP. This article will briefly introduce the introductory guide to PHP image processing.

1. Environmental requirements

To use PHP image processing, you first need the support of the PHP GD library. The library provides functions for writing images to files or outputting them to a browser, cropping and scaling images, adding text, and making images grayscale or inverting. Therefore, make sure your server has the PHP GD library installed.

2. Commonly used functions

1. imagecreatetruecolor() function

imagecreatetruecolor() function is used to create a true color image resource. For example:

$image = imagecreatetruecolor(200, 200);

2. imagecolorallocate() function

imagecolorallocate() function is used to assign a color to an image resource. For example:

$color = imagecolorallocate($image, 0, 0, 0);

Among them, $image is the image resource created before, and 0, 0, 0 represents the black RGB value.

3. imagefilledrectangle() function

The imagefilledrectangle() function is used to draw a rectangle filled with color in the image resource. For example:

imagefilledrectangle($image, 0, 0, 200, 200, $color);

where $color is the previously assigned color.

4. imagettftext() function

imagettftext() function is used to add a text to the image resource. For example:

$text_color = imagecolorallocate($image, 255, 255, 255);
imagettftext($image, 20, 0, 50, 100, $text_color, "arial.ttf", "Hello, PHP!");

Among them, 20 represents the font size, 0 represents the tilt angle, 50 and 100 are the coordinates of the upper left corner of the text, arial.ttf is the font file path, "Hello, PHP!" is the text to be output .

5. imagejpeg() function

The imagejpeg() function is used to output images into JPEG format. For example:

header("Content-Type: image/jpeg");
imagejpeg($image);

Among them, the header() function is used to set the Content-Type header of the output, telling the browser that the output is an image, and $image is the image resource created previously.

6. imagedestroy() function

The imagedestroy() function is used to destroy image resources. For example:

imagedestroy($image);

3. Basic image processing

1. Reading and outputting images

Reading and outputting images is very simple, just use imagecreatefromjpeg( ) and imagejpeg() functions. For example:

$image = imagecreatefromjpeg("example.jpg");
header("Content-Type: image/jpeg");
imagejpeg($image);
imagedestroy($image);

Among them, the imagecreatefromjpeg() function will read example.jpg as an image resource, the header() function sets the output Content-Type header, the imagejpeg() function outputs the image, and the imagedestroy() function destroys the image. resource.

2. Crop and scale images

To crop and scale images, you need to use the imagecopyresampled() function. For example:

$image = imagecreatefromjpeg("example.jpg");
$width = imagesx($image);
$height = imagesy($image);
$new_image = imagecreatetruecolor(100, 100);
imagecopyresampled($new_image, $image, 0, 0, 0, 0, 100, 100, $width, $height);
header("Content-Type: image/jpeg");
imagejpeg($new_image);
imagedestroy($image);
imagedestroy($new_image);

Among them, the first parameter of the imagecopyresampled() function is the new image resource, the second parameter is the old image resource, and the next four parameters are the X and Y in the upper left corner of the new image resource. Coordinates, X and Y coordinates of the upper left corner of the cropped image resource. The next two parameters are the width and height of the new image resource. The next two parameters are the width and height of the old image resource. Finally, destroy the image resource.

3. Add watermark

To add a watermark to an image, you need to use the imagecopy() function. For example:

$image = imagecreatefromjpeg("example.jpg");
$watermark = imagecreatefrompng("watermark.png");
$watermark_width = imagesx($watermark);
$watermark_height = imagesy($watermark);
imagecopy($image, $watermark, 0, 0, 0, 0, $watermark_width, $watermark_height);
header("Content-Type: image/jpeg");
imagejpeg($image);
imagedestroy($image);
imagedestroy($watermark);

Among them, the imagecreatefrompng() function reads the watermark as an image resource, and the imagecopy() function adds the watermark to example.jpg and destroys the image resource.

4. Advanced image processing

1. Image thumbnail

Image thumbnail is a very common requirement in web development, and the PHP GD library also provides it A very convenient function to generate thumbnails. For example:

$image = imagecreatefromjpeg("example.jpg");
$width = imagesx($image);
$height = imagesy($image);
$new_width = 100;
$new_height = ($new_width / $width) * $height;
$new_image = imagecreatetruecolor($new_width, $new_height);
imagecopyresampled($new_image, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
header("Content-Type: image/jpeg");
imagejpeg($new_image);
imagedestroy($image);
imagedestroy($new_image);

Among them, first read the original image, calculate the new width and height, use the imagecreatetruecolor() function to create a new image resource, and use the imagecopyresampled() function to shrink the old image to the new width and height. High, finally output a new image and destroy the image resource.

2. Image Filters

Image filters can add very cool effects to images. In the PHP GD library, this can be easily achieved using the imagefilter() function. For example:

$image = imagecreatefromjpeg("example.jpg");
imagefilter($image, IMG_FILTER_GRAYSCALE);
header("Content-Type: image/jpeg");
imagejpeg($image);
imagedestroy($image);

Among them, IMG_FILTER_GRAYSCALE is a grayscale filter, which can change the image to grayscale.

3. Image encoding and decoding

In web development, it is common to convert images to Base64 encoding for display in HTML. The PHP GD library provides imagejpeg() and imagepng() functions to directly output Base64 encoding. For example:

$image = imagecreatefromjpeg("example.jpg");
ob_start();
imagejpeg($image);
$data = ob_get_contents();
ob_clean();
$base64 = "data:image/jpeg;base64," . base64_encode($data);
echo "<img src="$base64">";
imagedestroy($image);

Among them, the ob_start() function turns on the output cache, the imagejpeg() function outputs the image to the cache, the ob_get_contents() function obtains the data in the cache, the ob_clean() function clears the cache, and the base64_encode() function Base64 encode the data in the cache, and finally generate an img tag with Base64 encoding as the value of its src attribute. Destroy image resources.

Conclusion

The above is an introductory guide to PHP image processing. Through this guide, you can understand the basic functions and common functions provided by the PHP GD library, and understand how to implement image processing through examples. and advanced image processing. I believe that beginners already have a certain understanding and practical basis. Of course, what is introduced here is only a very basic and simple function. I hope readers can learn and practice it in depth to provide more possibilities for their own Web development.

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