PHP sharpness convolution martix

I'm using a convolution matrix for sharpness in PHP GD and I want to change the开发者_StackOverflow sharpness "level".

Where would I make changes to this if I want to make it more or less sharp?

$image = imagecreatefromjpeg('pic.jpg');

$matrix = array(
  array(0, -1, 0), 
  array(-1, 5, -1), 
  array(0, -1, 0)
);

imageconvolution($image, $matrix, 1, 0.001);
header("Content-type: image/jpeg");
imagejpeg($image);

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try looking on http://www.gamedev.net/reference/programming/features/imageproc/page2.asp

There are lots of examples on the web, but as a rule of thumb you may try these params first in GIMP or PS or any other editor that has this function (image convolution is pretty common)

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What you really needed to do was use this formula

Where k = sharpness level.