There are two ways to change the size of an image. The imagecopyresized() function is fast but crude, and may lead to jagged edges in your new images. The imagecopyre sampled() function is slower, but features pixel interpolation to give smooth edges and clarity to the resized image.
Both functions take the same arguments:
imagecopyresized(dest, src, dx, dy, sx, sy, dw, dh, sw, sh);
imagecopyresampled(dest, src, dx, dy, sx, sy, dw, dh, sw, sh);
The dest and src parameters are image handles. The point (dx, dy) is the point in the destination image where the region will be copied. The point (sx, sy) is the upper-left corner of the source image. The sw, sh, dw, and dh parameters give the width and height of the copy regions in the source and destination
Example of Resizing with imagecopyresampled()
<?php
$source = imagecreatefromjpeg("php.jpg");
$width = imagesx($source);
$height = imagesy($source);
$x = $width / 2;
$y = $height / 2;
$destination = imagecreatetruecolor($x, $y);
imagecopyresampled($destination, $source, 0, 0, 0, 0, $x, $y, $width, $height);
header("Content-Type: image/png");
imagepng($destination);
?>