convert pdf colors from RGB to CMYK

Is there any php script/function to change the color odf PDF from RGB to CMYK ?

 

I'm not sure what you mean by "color odf PDF", but here's a php function to convert from RGB to CMYK. What you do with the resulting array is up to you.

/*
	Converts an array of RGB data to CMYK data.
	
	Parameters:
		$rgb	- 	an array of color information where
					$rgb[0] == red value
					$rgb[1] == green value
					$rgb[2] == blue value
	Returns:
		array containing cmyk color information:
			$array[0] == cyan value
			$array[1] == magenta value
			$array[2] == yellow value
			$array[3] == black value
*/
function RGB_to_CMYK($rgb)
{
    $cyan = 1 - ($rgb[0] / 255);
    $magenta = 1 - ($rgb[1] / 255);
    $yellow = 1 - ($rgb[2] / 255);

    $min = min($cyan, $magenta, $yellow);
    
	if ($min == 1)
        return array(0,0,0,1);

    $K = $min;
    $black = 1 - $K;

	return array
	(
		($cyan - $K) / $black,
		($magenta- $K) / $black,
		($yellow - $K) / $black,
		$K
	);
}

PHP:

 

I would be utterly amazed if that is all there is to converting RGB to cmyk. I figured that photoshop, etc. would have a complex algorithm for this.

varun - if correct, the above function would do absolutely nothing for your conversion hopes. All that is doing is changing 1 color to another (RGB --> CMYK) not converting a pdf or even a picture.

Being a graphic artist and a programmer, I can honestly tell you that I have looked and found nothing that will automate this process. If you are building the PDFs server side from a group of pictures and text it would be possible to convert the pictures then build the PDF in cmyk but if you already have a rendered PDF, it's not going to happen (to the best of my knowledge).

Good luck

 

Well...yes and no.

The algorithm is simple, and what I posted is it. That said, doing something useful with the output is another matter.

The conversion doesn't take into account any of the real-world factors you and I deal with every day: rich black, saturation, bleed, ICC profiles (for acquisition, display and output), and more.