PHP - Php Thump Crop

Hello everyone,
In fact, I have a script that makes the crop image that works well, I'm stuck on the part of adding a text box to allow to name the image "thumb".
I also ask if possible to remove the "PHP_SELF" script and divide it into several pages.
Attached script

There is a picture with dimensions of 10000 by 10000 pixels. Need to display a picture with dimensions of 200 by 100. Only need to use native php.

I need to set the width and let height adjust to the proportions of width. Can someone please help me with this?
I understand that $canvas_height should be 160, but then the image will crop to whichever side is greatest not by the width only.
Code: [Select]
<?php
 $img = "image.jpg";
 $canvas_width  = 160;
 $canvas_height = 0;

 list($img_width, $img_height) = getimagesize($img);

 $ratio_orig = $img_width / $img_height;

 if($canvas_width / $canvas_height > $ratio_orig)
 {
$canvas_width = $canvas_height * $ratio_orig;
 }
 else
 {
$canvas_height = $canvas_width / $ratio_orig;
 }

 $original = imagecreatefromjpeg($img);

 $canvas = imagecreatetruecolor($canvas_width, $canvas_height);

 imagecopyresampled($canvas, $original, 0, 0, 0, 0, $canvas_width, $canvas_height, $img_width, $img_height);

 $dest = "medium/image.jpg";
 imagejpeg($canvas, $dest, 100);
?>

I've been creating my own image upload script which takes in several parameters to style an image, however when the function is used new width and new height are specified but I need to use these values to determine cropping coordinates.

What I want is when a new width and height is specified, if it is squared i.e. new width is equal to new height AND the original image is not squared i.e. it is a vertical or horizontal rectangle then the central part of that image will be taken.

So for example if the user uploads an image 500px high and 100px wide and sets the new width and height both at 100px the new image should be a 100px by 100px square which is taken 200px from the top of the original image.

Here is the functions I currently use so far. It's just the coordinates function I can't seem to figure out. Can anyone please help me out:-

Code: [Select]

//gets the extension of an uploaded file
function getExtension($file) {
$i = strrpos($file,".");//Gets the position of the "." in the filename
if (!$i) { return ""; }//If there is no "." the function ends and returns ""     
$l = strlen($file) - $i;
$ext = substr($file,$i+1,$l);
$ext = strtolower($ext);
return $ext;
}

//checks image dimensions and scales both sizes by ratio if it exceeds the max
//$w = width, $mw = max width, $h = height, $mh = max height,
function checkSize($w, $mw, $h, $mh){

if($w > $mw){//Checks if width is greater than max width
$ratio = $mw / $w;
$h = $h * $ratio;
$h = round($h);
$w = $mw;
}

if($h > $mh){//Checks if height is greater than max height
$ratio = $mh / $h;
$w = $w * $ratio;
$w = round($w);
$h = $mh;
}

return array($w, $h);

}

//Used to get the coordinates to resize an image by
function getCoords(){


}

//$f = the file, $ext = file extension, $nw = new width, $nh = new height, $mw = max width, $mh = max height, $nf = new filename, $fo = folder, $des = file size description, $q = quality
function imageUpload($f, $ext, $nw, $nh, $mw, $mh, $nf, $fo, $des, $q){

//create image from uploaded file type
if($ext=="jpg" || $ext=="jpeg" ){
$src = imagecreatefromjpeg($f);
}else if($ext=="png"){
$src = imagecreatefrompng($f);
}else{
$src = imagecreatefromgif($f);
}

//creates a list of the width and height of the image
list($w,$h)=getimagesize($f);

//sets the coordinates for resizing to 0 by default
$dx = $dy = $sx = $sy = 0;

//if new width and height are both 0 then a resize is not required so original dimensions need to be validated in case they exceed their max
if($nw == 0 && $nh == 0){

if($w > $mw  || $h > $mh){//checks if width or height are greater than their max

list($w, $h) = checkSize($w, $mw, $h, $mh);

}

$nw = $w;
$nh = $h;

}else if($nw == $nh && $w !== $h){//this is for if the resized image needs to be squared but the original image is not a square

//COORDS FUNCTION NEEDED HERE

}

$desext = "";//sets the description extension to "" by default
if($des !== 0){//Checks if $des is set or not
$desext .= "_".$des;//appends des to $desext ready to be appended to the filename
}

$foext = "";//sets the folder extension to "" by default
if($fo !== 0){//Checks if $fo is set or not
$foext .= $fo."/";//appends folder to $foext ready to be appended to the filename
}

$qv = 100;//sets the quality value to 100 percent by default
if($q !== 0){//Checks if $q is set or not
$qv .= $q;//sets the quality value to the passed value
}

$tmp=imagecreatetruecolor($nw,$nh);
imagecopyresampled($tmp,$src,$dx,$dy,$sx,$sy,$nw,$nh,$w,$h);
$fn = "images/".$foext.$nf.$desext.".jpg";//sets the final filename for upload
imagejpeg($tmp,$fn,$qv);//uploads the file

//empty variables and clear image
imagedestroy($src);
imagedestroy($tmp);

}

I'll explain with an example:
I have this image: http://www.fitnessvital.com/images/galeria/caballo-pastando-0.jpg
I create a thumbnail of it: http://www.fitnessvital.com/images/galeria/thumbs/caballo-pastando-0.jpg

You can see that it's a big image where the important thing is the horse. The grass is not important.
So, the best thing to do it's to crop the extra grass and resizing the rest.

So the question is:
There's a way of recognizing the objects of an image and crop the rest ? Or identify the non important of an imagen and cropt it ? (the same rewrited)

Thank you