para eso es la libreria GD (sirve para no distorcionar las imagenes)
ejemplo
si alguien sube una imagen un rectangulo y quieres que se muestre en un cuadrito, en lugar de estirar la imagen va a crear otra mucho mas pequeña tanto en peso como tamaño pero la foto original ba a estar guardada en una carpeta para que no se pierda
Después de copiar el codigo y ponerlo en alguna carpeta, supongamos que lo pusiste "librerias" y la imagen que quieres redimensionar a 200x150 pixeles es "laimagen.png" que se ubica en la carpeta "tusimagenes", solo escribes en el SRC de tu <img>:
/librerias/image.php?image=/tusimagenes/laimagen.png&width=200&height=150
Saludos. nota: tambien sirve para png y jpg pero no sirve para gifs animados
CREAS UN ARCHIVO image.php
Código PHP:
<?php
if (!isset($_GET['image']))
{
header('HTTP/1.1 400 Bad Request');
echo 'Error: no image was specified';
exit();
}
define('MEMORY_TO_ALLOCATE', '100M');
define('DEFAULT_QUALITY', 90);
define('CURRENT_DIR', dirname(__FILE__));
define('CACHE_DIR_NAME', '/imagecache/');
define('CACHE_DIR', CURRENT_DIR . CACHE_DIR_NAME);
define('DOCUMENT_ROOT', $_SERVER['DOCUMENT_ROOT']);
$image = preg_replace('/^(s?f|ht)tps?:\/\/[^\/]+/i', '', (string) $_GET['image']);
if ($image{0} != '/' || strpos(dirname($image), ':') || preg_match('/(\.\.|<|>)/', $image))
{
header('HTTP/1.1 400 Bad Request');
echo 'Error: malformed image path. Image paths must begin with \'/\'';
exit();
}
if (!$image)
{
header('HTTP/1.1 400 Bad Request');
echo 'Error: no image was specified';
exit();
}
$docRoot = preg_replace('/\/$/', '', DOCUMENT_ROOT);
if (!file_exists($docRoot . $image))
{
header('HTTP/1.1 404 Not Found');
echo 'Error: image does not exist: ' . $docRoot . $image;
exit();
}
$size = GetImageSize($docRoot . $image);
$mime = $size['mime'];
if (substr($mime, 0, 6) != 'image/')
{
header('HTTP/1.1 400 Bad Request');
echo 'Error: requested file is not an accepted type: ' . $docRoot . $image;
exit();
}
$width = $size[0];
$height = $size[1];
$maxWidth = (isset($_GET['width'])) ? (int) $_GET['width'] : 0;
$maxHeight = (isset($_GET['height'])) ? (int) $_GET['height'] : 0;
if (isset($_GET['color']))
$color = preg_replace('/[^0-9a-fA-F]/', '', (string) $_GET['color']);
else
$color = FALSE;
if (!$maxWidth && $maxHeight)
{
$maxWidth = 99999999999999;
}
elseif ($maxWidth && !$maxHeight)
{
$maxHeight = 99999999999999;
}
elseif ($color && !$maxWidth && !$maxHeight)
{
$maxWidth = $width;
$maxHeight = $height;
}
if ((!$maxWidth && !$maxHeight) || (!$color && $maxWidth >= $width && $maxHeight >= $height))
{
$data = file_get_contents($docRoot . '/' . $image);
$lastModifiedString = gmdate('D, d M Y H:i:s', filemtime($docRoot . '/' . $image)) . ' GMT';
$etag = md5($data);
doConditionalGet($etag, $lastModifiedString);
header("Content-type: $mime");
header('Content-Length: ' . strlen($data));
echo $data;
exit();
}
$offsetX = 0;
$offsetY = 0;
if (isset($_GET['cropratio']))
{
$cropRatio = explode(':', (string) $_GET['cropratio']);
if (count($cropRatio) == 2)
{
$ratioComputed = $width / $height;
$cropRatioComputed = (float) $cropRatio[0] / (float) $cropRatio[1];
if ($ratioComputed < $cropRatioComputed)
{
$origHeight = $height;
$height = $width / $cropRatioComputed;
$offsetY = ($origHeight - $height) / 2;
}
else if ($ratioComputed > $cropRatioComputed)
{
$origWidth = $width;
$width = $height * $cropRatioComputed;
$offsetX = ($origWidth - $width) / 2;
}
}
}
$xRatio = $maxWidth / $width;
$yRatio = $maxHeight / $height;
if ($xRatio * $height < $maxHeight)
{
$tnHeight = ceil($xRatio * $height);
$tnWidth = $maxWidth;
}
else
{
$tnWidth = ceil($yRatio * $width);
$tnHeight = $maxHeight;
}
$quality = (isset($_GET['quality'])) ? (int) $_GET['quality'] : DEFAULT_QUALITY;
$resizedImageSource = $tnWidth . 'x' . $tnHeight . 'x' . $quality;
if ($color)
$resizedImageSource .= 'x' . $color;
if (isset($_GET['cropratio']))
$resizedImageSource .= 'x' . (string) $_GET['cropratio'];
$resizedImageSource .= '-' . $image;
$resizedImage = md5($resizedImageSource);
$resized = CACHE_DIR . $resizedImage;
if (!isset($_GET['nocache']) && file_exists($resized))
{
$imageModified = filemtime($docRoot . $image);
$thumbModified = filemtime($resized);
if($imageModified < $thumbModified) {
$data = file_get_contents($resized);
$lastModifiedString = gmdate('D, d M Y H:i:s', $thumbModified) . ' GMT';
$etag = md5($data);
doConditionalGet($etag, $lastModifiedString);
header("Content-type: $mime");
header('Content-Length: ' . strlen($data));
echo $data;
exit();
}
}
ini_set('memory_limit', MEMORY_TO_ALLOCATE);
$dst = imagecreatetruecolor($tnWidth, $tnHeight);
switch ($size['mime'])
{
case 'image/gif':
$creationFunction = 'ImageCreateFromGif';
$outputFunction = 'ImagePng';
$mime = 'image/png';
$doSharpen = FALSE;
$quality = round(10 - ($quality / 10));
break;
case 'image/x-png':
case 'image/png':
$creationFunction = 'ImageCreateFromPng';
$outputFunction = 'ImagePng';
$doSharpen = FALSE;
$quality = round(10 - ($quality / 10));
break;
default:
$creationFunction = 'ImageCreateFromJpeg';
$outputFunction = 'ImageJpeg';
$doSharpen = TRUE;
break;
}
$src = $creationFunction($docRoot . $image);
if (in_array($size['mime'], array('image/gif', 'image/png')))
{
if (!$color)
{
imagealphablending($dst, false);
imagesavealpha($dst, true);
}
else
{
if ($color[0] == '#')
$color = substr($color, 1);
$background = FALSE;
if (strlen($color) == 6)
$background = imagecolorallocate($dst, hexdec($color[0].$color[1]), hexdec($color[2].$color[3]), hexdec($color[4].$color[5]));
else if (strlen($color) == 3)
$background = imagecolorallocate($dst, hexdec($color[0].$color[0]), hexdec($color[1].$color[1]), hexdec($color[2].$color[2]));
if ($background)
imagefill($dst, 0, 0, $background);
}
}
ImageCopyResampled($dst, $src, 0, 0, $offsetX, $offsetY, $tnWidth, $tnHeight, $width, $height);
if ($doSharpen)
{
$sharpness = findSharp($width, $tnWidth);
$sharpenMatrix = array(
array(-1, -2, -1),
array(-2, $sharpness + 12, -2),
array(-1, -2, -1)
);
$divisor = $sharpness;
$offset = 0;
imageconvolution($dst, $sharpenMatrix, $divisor, $offset);
}
if (!file_exists(CACHE_DIR))
mkdir(CACHE_DIR, 0755);
if (!is_readable(CACHE_DIR))
{
header('HTTP/1.1 500 Internal Server Error');
echo 'Error: the cache directory is not readable';
exit();
}
else if (!is_writable(CACHE_DIR))
{
header('HTTP/1.1 500 Internal Server Error');
echo 'Error: the cache directory is not writable';
exit();
}
$outputFunction($dst, $resized, $quality);
ob_start();
$outputFunction($dst, null, $quality);
$data = ob_get_contents();
ob_end_clean();
ImageDestroy($src);
ImageDestroy($dst);
$lastModifiedString = gmdate('D, d M Y H:i:s', filemtime($resized)) . ' GMT';
$etag = md5($data);
doConditionalGet($etag, $lastModifiedString);
header("Content-type: $mime");
header('Content-Length: ' . strlen($data));
echo $data;
function findSharp($orig, $final)
{
$final = $final * (750.0 / $orig);
$a = 52;
$b = -0.27810650887573124;
$c = .00047337278106508946;
$result = $a + $b * $final + $c * $final * $final;
return max(round($result), 0);
}
function doConditionalGet($etag, $lastModified)
{
header("Last-Modified: $lastModified");
header("ETag: \"{$etag}\"");
$if_none_match = isset($_SERVER['HTTP_IF_NONE_MATCH']) ?
stripslashes($_SERVER['HTTP_IF_NONE_MATCH']) :
false;
$if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ?
stripslashes($_SERVER['HTTP_IF_MODIFIED_SINCE']) :
false;
if (!$if_modified_since && !$if_none_match)
return;
if ($if_none_match && $if_none_match != $etag && $if_none_match != '"' . $etag . '"')
return;
if ($if_modified_since && $if_modified_since != $lastModified)
return;
header('HTTP/1.1 304 Not Modified');
exit();
}
?>