Class that generates images in custom size keeping the aspect ratio. If the image does not exist, will be generated and saved in the folder mentioned and printed on the screen. If the image already exists in the reported dimensions, the image will be printed on the screen.

generate-images-custom-dimensions-keeping-proportion-dinamic.php

<?php 
class image{
public function createthumb_estadio($id, $name, $new_w, $new_h) {
    $border=false; $transparency=true; $base64=false;
    $name_ = $name;
    $name = "images/estadios/{$id}/{$name}";
    $newname = "images/estadios/$id/".$new_w."_".$new_h.$name_;
    if(file_exists($newname)){
         switch (exif_imagetype($newname)) {
            case IMAGETYPE_PNG:
                header('Content-Type: image/png');
                 echo file_get_contents($newname);
                break;
            case IMAGETYPE_GIF:
                header('Content-Type: image/gif');
                echo file_get_contents($newname);
                break;
            case IMAGETYPE_JPEG:
            default:
                header('Content-Type: image/jpeg');
                echo file_get_contents($newname);
                break;
        }
        exit;
    }
    if(!file_exists($name))
        return false;
    $arr = explode(".",$name);
    $ext = $arr[count($arr)-1];

    if($ext=="jpeg" || $ext=="jpg"){
        $img = @imagecreatefromjpeg($name);
    } elseif($ext=="png"){
        $img = @imagecreatefrompng($name);

    } elseif($ext=="gif") {
        $img = @imagecreatefromgif($name);
    }
    if(!$img)
        return false;
    $old_x = imageSX($img);
    $old_y = imageSY($img);
    if($old_x < 150 AND $old_y < 200){
        $thumb_w = $old_x;
        $thumb_h = $old_y;
    }else if($old_x < 200 AND $old_y < 150){
         $thumb_w = $old_x;
         $thumb_h = $old_y;
    }else{
        $ops = $this->scaleImage($old_x,$old_y,$new_w,$new_h);
        $thumb_w =  $ops[0];
        $thumb_h =  $ops[1];
    }
    $new_img = ImageCreateTrueColor($thumb_w, $thumb_h);
    if($transparency) {
        if($ext=="png") {
            imagealphablending($new_img, false);
            $colorTransparent = imagecolorallocatealpha($new_img, 0, 0, 0, 127);
            imagefill($new_img, 0, 0, $colorTransparent);
            imagesavealpha($new_img, true);
        } elseif($ext=="gif") {
            $trnprt_indx = imagecolortransparent($img);
            if ($trnprt_indx >= 0) {
                //its transparent
                $trnprt_color = imagecolorsforindex($img, $trnprt_indx);
                $trnprt_indx = imagecolorallocate($new_img, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);
                imagefill($new_img, 0, 0, $trnprt_indx);
                imagecolortransparent($new_img, $trnprt_indx);
            }
        }
    } else {
        Imagefill($new_img, 0, 0, imagecolorallocate($new_img, 255, 255, 255));
    }
    imagecopyresampled($new_img, $img, 0,0,0,0, $thumb_w, $thumb_h, $old_x, $old_y); 
    if($border) {
        $black = imagecolorallocate($new_img, 0, 0, 0);
        imagerectangle($new_img,0,0, $thumb_w, $thumb_h, $black);
    }
    if($base64) {
        ob_start();
        imagepng($new_img);
        $img = ob_get_contents();
        ob_end_clean();
        $return = base64_encode($img);
    } else {
        if($ext=="jpeg" || $ext=="jpg"){
            header("Content-type: image/jpeg");
            imagejpeg($new_img);
            imagejpeg($new_img,$newname);
        } elseif($ext=="png"){
             header("Content-type: image/png");
             imagepng($new_img);
             imagepng($new_img,$newname);
        } elseif($ext=="gif") {
            header("Content-type: image/gif");
            imagegif($new_img);
            imagegif($new_img,$newname);
        }
    }
}
    public function scaleImage($x,$y,$cx,$cy) {
        //Set the default NEW values to be the old, in case it doesn't even need scaling
        list($nx,$ny)=array($x,$y);
        //If image is generally smaller, don't even bother
        if ($x>=$cx || $y>=$cx) {
            //Work out ratios
            if ($x>0) $rx=$cx/$x;
            if ($y>0) $ry=$cy/$y;
            //Use the lowest ratio, to ensure we don't go over the wanted image size
            if ($rx>$ry) {
                $r=$ry;
            } else {
                $r=$rx;
            }
            //Calculate the new size based on the chosen ratio
            $nx=intval($x*$r);
            $ny=intval($y*$r);
        }
        //Return the results
        return array($nx,$ny);
    }
}

?>