Last updated: Fri, 05 Sep 2008

imagefilter

(PHP 5)

imagefilter — Applies a filter to an image

Description

bool imagefilter ( resource $image , int $filtertype [, int $arg1 [, int $arg2 [, int $arg3 [, int $arg4 ]]]] )

imagefilter() applies the given filter filtertype on the image .

Parameters

image

An 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.
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 , blue , green 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.

arg1

IMG_FILTER_BRIGHTNESS: Brightness level.
IMG_FILTER_CONTRAST: Contrast level.
IMG_FILTER_COLORIZE: Value of red component.
IMG_FILTER_SMOOTH: Smoothness level.

arg2

IMG_FILTER_COLORIZE: Value of green component.

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.

Return Values

Returns TRUE on success or FALSE on failure.

ChangeLog

Version	Description
5.2.5	Alpha support for `IMG_FILTER_COLORIZE` was added.

Examples

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.';
}
?>

Notes

Note: This function is only available if PHP is compiled with the bundled version of the GD library.


Function to change the transparency of a png image on the fly. Works only with PNG, and with a browser supporting alpha channel.

The function stretches the opacity-range of the image, so that the most opaque pixel(s) will be set to the given opacity. (Other opacity values in pixels are modified accordingly.)

Returns success or failure.



<?php

function filter_opacity( &$img, $opacity ) //params: image resource id, opacity in percentage (eg. 80)

        {

            if( !isset( $opacity ) )

                { return false; }

            $opacity /= 100;

            

            //get image width and height

            $w = imagesx( $img );

            $h = imagesy( $img );

            

            //turn alpha blending off

            imagealphablending( $img, false );

            

            //find the most opaque pixel in the image (the one with the smallest alpha value)

            $minalpha = 127;

            for( $x = 0; $x < $w; $x++ )

                for( $y = 0; $y < $h; $y++ )

                    {

                        $alpha = ( imagecolorat( $img, $x, $y ) >> 24 ) & 0xFF;

                        if( $alpha < $minalpha )

                            { $minalpha = $alpha; }

                    }

            

            //loop through image pixels and modify alpha for each

            for( $x = 0; $x < $w; $x++ )

                {

                    for( $y = 0; $y < $h; $y++ )

                        {

                            //get current alpha value (represents the TANSPARENCY!)

                            $colorxy = imagecolorat( $img, $x, $y );

                            $alpha = ( $colorxy >> 24 ) & 0xFF;

                            //calculate new alpha

                            if( $minalpha !== 127 )

                                { $alpha = 127 + 127 * $opacity * ( $alpha - 127 ) / ( 127 - $minalpha ); }

                            else

                                { $alpha += 127 * $opacity; }

                            //get the color index with new alpha

                            $alphacolorxy = imagecolorallocatealpha( $img, ( $colorxy >> 16 ) & 0xFF, ( $colorxy >> 8 ) & 0xFF, $colorxy & 0xFF, $alpha );

                            //set pixel with the new color + opacity

                            if( !imagesetpixel( $img, $x, $y, $alphacolorxy ) )

                                { return false; }

                        }

                }

            return true;

        }

?>



Example for use:



 <?php

  $image = imagecreatefrompng( "img.png" );

  filter_opacity( $image, 75 );

  header( "content-type: image/png" );

  imagepng( $image );

  imagedestroy( $image );

?>

Kae Cyphet
02-Dec-2007 10:23


To solve that annoying problem of having to install a pre-compiled version of GD just to get imagefilter($image,IMAGE_FILTER_NEGATE) working.



here is an open source solution.

uses the standard stuff included in php when you uncomment 'extension=php_gd2.dll' in the php.ini file and there ya go!



Useage:

<?php

$im = imagecreatefromjpeg("my_fav_image.jpg");



header("Content-type: image/jpg");

imagejpeg(invertimage($im));



imagedestroy($im);

?>



'=================================



<?php

function int2rgb($myint)

{

  return array('red' => 0xFF & ($myint >> 0x10), 'green' => 0xFF & ($myint >> 0x8), 'blue' => 0xFF & $myint);

}



function invertimage($im)

{

 $wid = imagesx($im);

 $hei = imagesy($im);

 $im2 = imagecreatetruecolor($wid,$hei);

 $i=0;

 $j=0;

 $rgb = array('red' => 0, 'green' => 0, 'blue' => 0);

 $ref = 0;



 for($i = 0;$i < $wid; $i++)

 {

  for($j = 0;$j < $hei; $j++)

  {

   $rgb = int2rgb(imagecolorat($im,$i,$j));

   $ref = imagecolorallocate($im2,255 - intval($rgb['red']),255 - intval($rgb['green']),255 - intval($rgb['blue']));

   imagesetpixel($im2,$i,$j,$ref);

  }

 }

 return $im2;

}

?>

michaeln no at spam associationsplus ca
21-Nov-2007 02:11


Note: applying IMG_FILTER_EMBOSS to text and using in a customization to the CAPTCHA image script in phpBB or a project of your own is a very good way to stop OCR-ing bots from getting through. Embossed serif fonts are fairly easy for the human eye to understand but to an OCR script it is extremely difficult because it seems to give it the illusion of 3D. 



If you only allocate 2 or 3 colours in the image, it uses the background colour alot in the embossed text, which greatly contributes to this.



I made my own custom CAPTCHA script to stop phpBB post spam for a client site I was developing and I have gone from getting 2-3 new spam users created every day to zero.



Anything with the source code freely available out there right now is possible to be defeated by spammers once one of them stars sharing code with the other spammers, but if you run something at least someone custom, their bots will pass you over.

ssttoo at gmail dot com
13-Nov-2007 06:31


Here's a page that shows the different filters in action

http://www.phpied.com/image-fun-with-php-part-2/

Also shows some quick ways to do sepia.

admin at phpgfx dot com
26-Aug-2007 01:52


this is a sepia function using microsoft's definition



<?php



function imagesepia( $img ) {

    $total = imagecolorstotal( $img );

    for ( $i = 0; $i < $total; $i++ ) {

        $index = imagecolorsforindex( $img, $i );

        $red = ( $index["red"] * 0.393 + $index["green"] * 0.769 + $index["blue"] * 0.189 ) / 1.351;

        $green = ( $index["red"] * 0.349 + $index["green"] * 0.686 + $index["blue"] * 0.168 ) / 1.203;

        $blue = ( $index["red"] * 0.272 + $index["green"] * 0.534 + $index["blue"] * 0.131 ) / 2.140;

        imagecolorset( $img, $i, $red, $green, $blue );

    }

}



?>

webmaster at designsbykosi dot info
08-May-2007 04:56


This will only work if you have php5. For php4, you'll have to use the sepia function set webmaster at qudi dot de suggested.

fananf at nerdshack dot com
16-Mar-2007 02:26


If you're looking for fast sepia effect that can be used for on-the-fly thumbnails generation you can't use sophisticated functions. The faster and much better way than described by webmaster at qudi dot de in the note from 31-Jan-2006 is applying colorize filter AFTER grayscale.



<?php



(...)



imagefilter($yourimage, IMG_FILTER_GRAYSCALE); imagefilter($yourimage, IMG_FILTER_COLORIZE, 90, 60, 40); 



(...)



?>



I used (90,60,40) for my sepia after couple of tests, however, if you need darker or lighter just check what suits you best.

trucex email over at gmail
14-Feb-2007 05:31


It appears that imagefilter doesn't play nice with apha. If you run an imagefilter on a transparent image it'll return a black image...similar to a lot of Photoshop plugins do.

PanuWorld
14-Jan-2007 11:55


The documentation misses the exact meaning and valid ranges of the arguments for ImageFilter(). According to the 5.2.0 sources the arguments are:

IMG_FILTER_BRIGHTNESS

-255 = min brightness, 0 = no change, +255 = max brightness



IMG_FILTER_CONTRAST

-100 = max contrast, 0 = no change, +100 = min contrast (note the direction!)



IMG_FILTER_COLORIZE

Adds (subtracts) specified RGB values to each pixel. The valid range for each color is -255...+255, not 0...255. The correct order is red, green, blue.

-255 = min, 0 = no change, +255 = max

This has not much to do with IMG_FILTER_GRAYSCALE.



IMG_FILTER_SMOOTH

Applies a 9-cell convolution matrix where center pixel has the weight arg1 and others weight of 1.0. The result is normalized by dividing the sum with arg1 + 8.0 (sum of the matrix).

any float is accepted, large value (in practice: 2048 or more) = no change



ImageFilter seem to return false if the argument(s) are out of range for the chosen filter.

nancy at hypertextdigital dot com
03-Aug-2006 06:16


This routine was just what I was looking for, I wanted web admin users to be able to recolour their uploaded photos (to go with a news item) either a blue tint or sepia to match the appearance of other colours used on the website. 



Using a form with a select box containing the RGB values, I can give them the option of either of the two tints or no colourization at all, plus resize their images to the viewing size and a thumbnail image on the fly without having to use any other image editing software.

santibari at fibertel dot com
27-Feb-2006 04:37


A colorize algorithm wich preserves color luminosity (i.e black 

will output black, and white will output white).

This works in PHP4 and is great for customizing interfaces 

dinamically.



<?php

function colorize($img_src,$img_dest, $r, $g, $b) 

{

if(!$im = imagecreatefromgif($img_src))

  return "Could not use image $img_src"; 

    

//We will create a monochromatic palette based on

//the input color

//which will go from black to white

//Input color luminosity: this is equivalent to the 

//position of the input color in the monochromatic

//palette

$lum_inp=round(255*($r+$g+$b)/765); //765=255*3



//We fill the palette entry with the input color at its 

//corresponding position



$pal[$lum_inp]['r']=$r;

$pal[$lum_inp]['g']=$g;

$pal[$lum_inp]['b']=$b;



//Now we complete the palette, first we'll do it to

//the black,and then to the white.



//FROM input to black

//===================

//how many colors between black and input

$steps_to_black=$lum_inp;        



//The step size for each component

if($steps_to_black)

 {

 $step_size_red=$r/$steps_to_black;    

 $step_size_green=$g/$steps_to_black;    

 $step_size_blue=$b/$steps_to_black;    

 }



for($i=$steps_to_black;$i>=0;$i--)

 {

 $pal[$steps_to_black-$i]['r']=$r-round($step_size_red*$i);

 $pal[$steps_to_black-$i]['g']=$g-round($step_size_green*$i);

 $pal[$steps_to_black-$i]['b']=$b-round($step_size_blue*$i);

 }



//From input to white:

//===================

//how many colors between input and white

$steps_to_white=255-$lum_inp;



if($steps_to_white)

  {

  $step_size_red=(255-$r)/$steps_to_white;    

  $step_size_green=(255-$g)/$steps_to_white;    

  $step_size_blue=(255-$b)/$steps_to_white;    

  }

 else

  $step_size_red=$step_size_green=$step_size_blue=0;



 //The step size for each component

 for($i=($lum_inp+1);$i<=255;$i++)

  {

  $pal[$i]['r']=$r + round($step_size_red*($i-$lum_inp));

  $pal[$i]['g']=$g + round($step_size_green*($i-$lum_inp));

  $pal[$i]['b']=$b + round($step_size_blue*($i-$lum_inp));

  }

//--- End of palette creation



//Now,let's change the original palette into the one we

//created

for($c = 0; $c < $palette_size; $c++)

 { 

 $col = imagecolorsforindex($im, $c);          

 $lum_src=round(255*($col['red']+$col['green']

                +$col['blue'])/765);

 $col_out=$pal[$lum_src];

 imagecolorset($im, $c, $col_out['r'], 

                                $col_out['g'],

                                $col_out['b']);

 }



 //save the image file

 imagepng($im,$img_dest);

 imagedestroy($im);

}//end function colorize

?>

webmaster at qudi dot de
31-Jan-2006 11:53


for a quick, ok-looking, sepia-effect (also in php4) I just use this little fellow, since a real implementation of sepia was just way too slow.



function pseudosepia(&$im,$percent){

      $sx=imagesx($im);

      $sy=imagesy($im);

      $filter=imagecreatetruecolor($sx,$sy);

      $c=imagecolorallocate($filter,100,50,50);

      imagefilledrectangle($filter,0,0,$sx,$sy,$c);

      imagecopymerge($im,$filter,0,0,0,0,$sx,$sy,$percent);

}

a php user at nowhere dot com
20-Dec-2005 05:48


http://www.hudzilla.org/phpbook/read.php/11_2_15

for more detailed info, and some <i>arg</i> guidelines.

vdepizzol at hotmail dot com
04-Sep-2004 05:36


Examples using imagefilter():



<?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);

?>



/////////////////////////////



<?php

$im = imagecreatefrompng('sean.png');

if ($im && imagefilter($im, IMG_FILTER_BRIGHTNESS, 20)) {

    echo 'Image brightness changed.';

    imagepng($im, 'sean.png');

} else {

    echo 'Image brightness change failed.';

}



imagedestroy($im);

?>



/////////////////////////////



<?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');

} else {

    echo 'Green shading failed.';

}



imagedestroy($im);

?>

kees at tweakers dot net
20-Jul-2004 10:26


From what i have been able to find from this function, it accepts the following arguments:

        IMG_FILTER_NEGATE

        IMG_FILTER_GRAYSCALE

        IMG_FILTER_EDGEDETECT

        IMG_FILTER_GAUSSIAN_BLUR

        IMG_FILTER_SELECTIVE_BLUR

        IMG_FILTER_EMBOSS

        IMG_FILTER_MEAN_REMOVAL



The following arguments need one or more arguments.

        IMG_FILTER_SMOOTH, -1924.124

        IMG_FILTER_COLORIZE, -127.12, -127.98, 127

        IMG_FILTER_CONTRAST, -90

        IMG_FILTER_BRIGHTNESS, 98

        

I haven't tested them all, the names speak for themselves.

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