(PHP 5, PHP 7)
imagefilter — Applies a filter to an image
$image
   , int $filtertype
   [, int $arg1
   [, int $arg2
   [, int $arg3
   [, int $arg4
  ]]]] )
   imagefilter() applies the given filter
   filtertype on the image.
  
imageAn image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
filtertype
       filtertype can be one of the following:
       
IMG_FILTER_NEGATE: Reverses all colors of
          the image.
         
        IMG_FILTER_GRAYSCALE: Converts the image into
          grayscale.
         
        IMG_FILTER_BRIGHTNESS: Changes the brightness
          of the image. Use arg1 to set the level of
          brightness. The range for the brightness is -255 to 255.
         
        IMG_FILTER_CONTRAST: Changes the contrast of
          the image. Use arg1 to set the level of
          contrast.
         
        IMG_FILTER_COLORIZE: Like
          IMG_FILTER_GRAYSCALE, except you can specify the
          color. Use arg1, arg2 and
          arg3 in the form of
          red, green,
          blue and arg4 for the
          alpha channel. The range for each color is 0 to 255.
         
        IMG_FILTER_EDGEDETECT: Uses edge detection to
          highlight the edges in the image.
         
        IMG_FILTER_EMBOSS: Embosses the image.
         
        IMG_FILTER_GAUSSIAN_BLUR: Blurs the image using
          the Gaussian method.
         
        IMG_FILTER_SELECTIVE_BLUR: Blurs the image.
         
        IMG_FILTER_MEAN_REMOVAL: Uses mean removal to
          achieve a "sketchy" effect.
         
        IMG_FILTER_SMOOTH: Makes the image smoother.
          Use arg1 to set the level of smoothness.
         
        IMG_FILTER_PIXELATE: Applies pixelation effect 
          to the image, use arg1 to set the block size 
          and arg2 to set the pixelation effect mode.
         
        arg1
IMG_FILTER_BRIGHTNESS: Brightness level.
         
        IMG_FILTER_CONTRAST: Contrast level.
         
        IMG_FILTER_COLORIZE: Value of red component.
         
        IMG_FILTER_SMOOTH: Smoothness level.
         
        IMG_FILTER_PIXELATE: Block size in pixels.
         
        arg2
IMG_FILTER_COLORIZE: Value of green component.
         
        IMG_FILTER_PIXELATE: Whether to use advanced pixelation 
          effect or not (defaults to FALSE).
         
        arg3
IMG_FILTER_COLORIZE: Value of blue component.
         
        arg4
IMG_FILTER_COLORIZE: Alpha channel, A value 
          between 0 and 127. 0 indicates completely opaque while 127 indicates 
          completely transparent.
         
        
   Returns TRUE on success or FALSE on failure.
  
| Version | Description | 
|---|---|
| 5.3.0 | Pixelation support ( IMG_FILTER_PIXELATE) was added. | 
| 5.2.5 | Alpha support for IMG_FILTER_COLORIZEwas added. | 
Example #1 imagefilter() grayscale example
<?php
$im = imagecreatefrompng('dave.png');
if($im && imagefilter($im, IMG_FILTER_GRAYSCALE))
{
    echo 'Image converted to grayscale.';
    imagepng($im, 'dave.png');
}
else
{
    echo 'Conversion to grayscale failed.';
}
imagedestroy($im);
?>
Example #2 imagefilter() brightness example
<?php
$im = imagecreatefrompng('sean.png');
if($im && imagefilter($im, IMG_FILTER_BRIGHTNESS, 20))
{
    echo 'Image brightness changed.';
    imagepng($im, 'sean.png');
    imagedestroy($im);
}
else
{
    echo 'Image brightness change failed.';
}
?>
Example #3 imagefilter() colorize example
<?php
$im = imagecreatefrompng('philip.png');
/* R, G, B, so 0, 255, 0 is green */
if($im && imagefilter($im, IMG_FILTER_COLORIZE, 0, 255, 0))
{
    echo 'Image successfully shaded green.';
    imagepng($im, 'philip.png');
    imagedestroy($im);
}
else
{
    echo 'Green shading failed.';
}
?>
Example #4 imagefilter() negate example
<?php
// Define our negate function so its portable for 
// php versions without imagefilter()
function negate($im)
{
    if(function_exists('imagefilter'))
    {
        return imagefilter($im, IMG_FILTER_NEGATE);
    }
    for($x = 0; $x < imagesx($im); ++$x)
    {
        for($y = 0; $y < imagesy($im); ++$y)
        {
            $index = imagecolorat($im, $x, $y);
            $rgb = imagecolorsforindex($index);
            $color = imagecolorallocate($im, 255 - $rgb['red'], 255 - $rgb['green'], 255 - $rgb['blue']);
            imagesetpixel($im, $x, $y, $color);
        }
    }
    return(true);
}
$im = imagecreatefromjpeg('kalle.jpg');
if($im && negate($im))
{
    echo 'Image successfully converted to negative colors.';
    imagejpeg($im, 'kalle.jpg', 100);
    imagedestroy($im);
}
else
{
    echo 'Converting to negative colors failed.';
}
?>
Example #5 imagefilter() pixelate example
<?php
// Load the PHP logo, we need to create two instances 
// to show the differences
$logo1 = imagecreatefrompng('./php.png');
$logo2 = imagecreatefrompng('./php.png');
// Create the image instance we want to show the 
// differences on
$output = imagecreatetruecolor(imagesx($logo1) * 2, imagesy($logo1));
// Apply pixelation to each instance, with a block 
// size of 3
imagefilter($logo1, IMG_FILTER_PIXELATE, 3);
imagefilter($logo2, IMG_FILTER_PIXELATE, 3, true);
// Merge the differences onto the output image
imagecopy($output, $logo1, 0, 0, 0, 0, imagesx($logo1) - 1, imagesy($logo1) - 1);
imagecopy($output, $logo2, imagesx($logo2), 0, 0, 0, imagesx($logo2) - 1, imagesy($logo2) - 1);
imagedestroy($logo1);
imagedestroy($logo2);
// Output the differences
header('Content-Type: image/png');
imagepng($output);
imagedestroy($output);
?>
The above example will output something similar to:
