Rotating and Flipping Images with PHP GD: Using imagerotate and Custom Functions

Image rotation and flipping are common tasks in web projects, but they are distinct concepts: rotation turns an image by a specific angle, while flipping mirrors the image along a chosen axis. Rotation can be performed directly with the GD library's imagerotate() function, whose prototype is:

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

The function rotates src_im by angle degrees, fills uncovered areas with bgd_color , and rotates around the image centre; the result is scaled to fit the original dimensions. Setting ignore_transparent to a non‑zero value discards transparent pixels.

Below is a PHP example that defines a rotate() function to rotate a JPEG image by a given number of degrees and saves the result back to the original file:

<?php
// Rotate an image by a given angle (JPEG example)
function rotate($filename, $degrees) {
    // Create image resource
    $source = imagecreatefromjpeg($filename);
    // Rotate using imagerotate()
    $rotate = imagerotate($source, $degrees, 0);
    // Save the rotated image
    imagejpeg($rotate, $filename);
}
// Rotate brophp.jpg by 180 degrees
rotate("brophp.jpg", 180);
?>

Flipping an image cannot be done with an arbitrary angle; it is limited to two directions: horizontal flip along the Y‑axis or vertical flip along the X‑axis.

For a horizontal (Y‑axis) flip, the following turn_y() function copies each column of pixels from right to left into a new image resource and saves the result:

<?php
function turn_y($filename) {
    $back = imagecreatefromjpeg($filename);
    $width = imagesx($back);
    $height = imagesy($back);
    $new = imagecreatetruecolor($width, $height);
    for ($x = 0; $x < $width; $x++) {
        imagecopy($new, $back, $width - $x - 1, 0, $x, 0, 1, $height);
    }
    imagejpeg($new, $filename);
    imagedestroy($back);
    imagedestroy($new);
}
turn_y("brophp.jpg");
?>

For a vertical (X‑axis) flip, the turn_x() function mirrors the image top‑to‑bottom by copying each row of pixels from bottom to top:

<?php
function turn_x($filename) {
    $back = imagecreatefromjpeg($filename);
    $width = imagesx($back);
    $height = imagesy($back);
    $new = imagecreatetruecolor($width, $height);
    for ($y = 0; $y < $height; $y++) {
        imagecopy($new, $back, 0, $height - $y - 1, 0, $y, $width, 1);
    }
    imagejpeg($new, $filename);
    imagedestroy($back);
    imagedestroy($new);
}
turn_x("brophp.jpg");
?>

These examples demonstrate how to implement both rotation and axis‑specific flipping of JPEG images using PHP's GD extension.