How to change Image to jpg and set dpi to 300 using php?

Question

I have following code in a controller under pngtojpgAction() which I am calling using ajax.

Through this

$this->getRequest()->getParam('imagedata'));

statement I am getting a pattern like this data:image/jpeg;base64,/9j/4AAQSkZJR......AH9T796KtUV1HGf/Z

Which is a png image data.

now I am using following code to convert this png image to jpeg and to increase dpi to 300.

public function pngtojpgAction()   
    {
                        //Code to convert png to jpg image
            $input = imagecreatefrompng($this->getRequest()->getParam('imagedata'));
            $width=imagesx($input);
            $height=imagesy($input);
            $output = imagecreatetruecolor($width, $height);
            $white = imagecolorallocate($output,  255, 255, 255);
            imagefilledrectangle($output, 0, 0, $width, $height, $white);
            imagecopy($output, $input, 0, 0, 0, 0, $width, $height);


            ob_start();
            imagejpeg($output);
            $contents =  ob_get_contents();
            ob_end_clean();
             //echo 'data:image/jpeg;base64,'.base64_encode($contents); /*Up to here code works well*/          

             $jpgImage='data:image/jpeg;base64,'.base64_encode($contents);


             $image = file_get_contents($jpgImage);

             $image = substr_replace($image, pack("cnn", 1, 300, 300), 13, 5);

             header("Content-type: image/jpeg");
             header('Content-Disposition: attachment; filename="'.basename($jpgImage).'"');
             echo  $image;      

    }

using this

 $image = substr_replace($image, pack("cnn", 1, 300, 300), 13, 5);

I want to increase dpi of image to 300 dpi.

I am unable to change the image dpi using these line of code

 $jpgImage='data:image/jpeg;base64,'.base64_encode($contents);


             $image = file_get_contents($jpgImage);

             $image = substr_replace($image, pack("cnn", 1, 300, 300), 13, 5);

             header("Content-type: image/jpeg");
             header('Content-Disposition: attachment; filename="'.basename($jpgImage).'"');
             echo  $image;

I used this link as reference Change image dpi using php

Answer 1

After making some changes it worked for me.

public function pngtojpgAction()   
{
            //Code to convert png to jpg image
        $input = imagecreatefrompng($this->getRequest()->getParam('imagedata'));
        $width=imagesx($input);
        $height=imagesy($input);
        $output = imagecreatetruecolor($width, $height);
        $white = imagecolorallocate($output,  255, 255, 255);
        imagefilledrectangle($output, 0, 0, $width, $height, $white);
        imagecopy($output, $input, 0, 0, 0, 0, $width, $height);                  

        ob_start();
        imagejpeg($output);
        $contents =  ob_get_contents();
        //Converting Image DPI to 300DPI                
        $contents = substr_replace($contents, pack("cnn", 1, 300, 300), 13, 5);             
        ob_end_clean();     
        echo 'data:image/jpeg;base64,'.base64_encode($contents); 

}

Answer 2

I would use imagemagic instead:

convert Bird.jpg -density 300 Bird2.jpg

But you could allso do that with GD.

Link to class

$filename = 'Bird.jpg';
$source = imagecreatefromjpeg($filename);
list($width, $height) = getimagesize($filename);

$b = new Resampler;
$im = $b->resample($source, $height, $width, 300);

file_put_contents('Bird2.jpg', $im);

Tested on Windows enviroment.

Answer 3

Simple Code to Re-generate image with adjustable quality.

function compress_image($source_url, $destination_url, $quality) {
    $info = getimagesize($source_url);
    $image = imagecreatefromjpeg($source_url);
    imagejpeg($image, $destination_url, $quality);
    return $destination_url;
}
echo compress_image($_FILES["file"]["tmp_name"], "destination .jpg", 80);//Adjust Quality

Note: Ensure that the GD library for PHP is installed.