PDF to JPG conversion using PHP

问题:

I'm trying to convert PDF to IMG (JPG) with help PHP.

I'm using imagick extension.

this is my code

    $fp_pdf = fopen($pdf, 'rb');

    $img = new imagick(); // [0] can be used to set page number
    $img->readImageFile($fp_pdf);
    $img->setImageFormat( "jpg" );
    $img->setImageCompression(imagick::COMPRESSION_JPEG); 
    $img->setImageCompressionQuality(90); 

    $img->setResolution(300,300);

    $img->setImageUnits(imagick::RESOLUTION_PIXELSPERINCH);

    $data = $img->getImageBlob(); 

my source pdf file has right dimension (210x297 mm, like A4 has). And everything looks good. But my jpg has page dimension as 842x595 px, and DPI is 72.

and img file much more smaller on paper then pdf, when i had print it.

what is a proper way to make image file from pdf and make it so big as pdf (on paper)

回答1:

ImageMagick uses GhostScript to process JPEGs, so you'd do better to exec GhostScript directly, which would be much more efficient and give you more control. It would also be only 1 exec statement, instead of playing around with the IMagick functions.

回答2:

You could use imagemagick through exec() or similar, the shell arguments are much less verbose than the PHP extension.

$pdf_file = escapeshellarg( "mysafepdf.pdf" );
$jpg_file = escapeshellarg( "output.jpg" );

$result = 0;
exec( "convert -density 300 {$pdf_file} {$jpg_file}", null, $result );

// at this point $result should == 0 if the conversion was successful

It's the "-density" (which sets the DPI to read the source file as) option that specifically fixes your problem.

Also imagemagick by default uses a -quality setting of 92 for JPEG writing in most cases - so you probably don't need to explicitly declare it.

回答3:

It looks like you missed two setters:

Imagick::setImagePage() http://www.php.net/manual/en/function.imagick-setimagepage.php

And:

Imagick::setImageExtent() http://www.php.net/manual/en/function.imagick-setimageextent.php

In order to get the correct parameters for these functions, you may try the following:

$fp_pdf = fopen($pdf, 'rb');
$params=array();

    $img = new imagick(); 
    $img->readImageFile($fp_pdf);
    /*my modification: */$img->setImageUnits(imagick::RESOLUTION_PIXELSPERINCH);
    /*my modification: */$params=$img->identifyImage();
    $img->setImageFormat( "jpg" );
    $img->setImageCompression(imagick::COMPRESSION_JPEG); 
    $img->setImageCompressionQuality(90); 
    /*my modification: */$img->setPage($params['geometry']['width'], $params['geometry']['height'], 0, 0)
    /*my modification: */$img->setResolution($params['resolution']['x'], $params['resolution']['y']);
    $img->setImageUnits(imagick::RESOLUTION_PIXELSPERINCH);
    $data = $img->getImageBlob();

If you find that some others attributes should be set, then let me show you the information that $params is holding. It may proof useful for you:

$params=array(
    [imageName],
    [format], 
    [geometry] => Array
        (
            [width]
            [height] 
        )
    [type], 
    [colorSpace], 
    [resolution],
        (
            [x] 
            [y]
        )

    [units],
    [fileSize],
    [compression],
    [signature], 

)

To be honest, I'm not completely sure if this will work. Is just a try in order to help you. I sincerely hope it does.

回答4:

As mentioned before, setting the resolution before reading the file does the trick:

$fp_pdf = fopen($pdf, 'rb');

$img = new imagick(); // [0] can be used to set page number
$img->setResolution(300,300);
$img->readImageFile($fp_pdf);
$img->setImageFormat( "jpg" );
$img->setImageCompression(imagick::COMPRESSION_JPEG); 
$img->setImageCompressionQuality(90); 

$img->setImageUnits(imagick::RESOLUTION_PIXELSPERINCH);

$data = $img->getImageBlob(); 

回答5:

You have to call setResolution before reading the image. Otherwise imagemagick will use the default system dpi.