# PHP GD Library (Image Processing)

The **GD Library** allows you to define, draw, and manipulate images dynamically using PHP. It is commonly used for creating CAPTCHAs, resizing uploaded images, or generating charts.

---

## 1. Creating an Image
You can create a blank canvas or create an image from an existing file.

```php
// Create a 200x200 blank image
$image = imagecreatetruecolor(200, 200);

// Or create from existing file
// $image = imagecreatefromjpeg("photo.jpg");
```

## 2. Allocating Colors
Before drawing, you need to allocate colors. The first color allocated becomes the background color for palette-based images, but for true color images, you must fill the background manually.

```php
$white = imagecolorallocate($image, 255, 255, 255);
$black = imagecolorallocate($image, 0, 0, 0);
$red   = imagecolorallocate($image, 255, 0, 0);

// Fill background with white
imagefill($image, 0, 0, $white);
```

## 3. Drawing Shapes and Text
PHP provides various functions to draw on the canvas.

```php
// Draw a black line
imageline($image, 0, 0, 200, 200, $black);

// Draw a red rectangle
imagefilledrectangle($image, 50, 50, 150, 150, $red);

// Write a string (Font size 1-5)
imagestring($image, 5, 60, 90, "Hello GD!", $white);
```

## 4. Outputting the Image
You can either save the image to a file or output it directly to the browser.

```php
// Output to browser
header("Content-Type: image/png");
imagepng($image);

// OR Save to file
// imagepng($image, "my_image.png");
```

## 5. Cleaning Up
Always destroy the image resource to free up memory.

```php
imagedestroy($image);
```

[[programming/php/php]] [[programming/php/php-file-uploads]]