How to apply a filter to an image using imagefilter() function in PHP?

imagefilter() is an inbuilt function in PHP that is used to apply a given filter to an image.

Syntax

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

Parameters

imagefilter() takes six different parameters − $image, int $filtertype, int $arg1, int $arg2, int $arg3, int $arg4.

• $image − It holds the image resource.

• $filtertype − Specifies the filter to be used which is an integer.

Below are the given different image filter constants −

• IMG_FILTER_NEGATE − Reverses all the colors of an image.

• IMG_FILTER_GRAYSCALE − Converts the image into the grayscale by changing the red, green, and blue components to their weighted sum.

• IMG_FILTER_BRIGHTNESS − Changes the brightness of the image. arg1 is used to set the level of brightness. The range for the brightness is -255 to 255.

• IMG_FILTER_CONSTRAST − Changes the contrast of the image. $arg1 is used to set the level of contrast.

• IMG_FILTER_COLORIZE − This image filter is like the IMG_FILTER_GARYSCALE, except that we can specify the color, it uses the arguments arg1, arg2, and $arg3 in the form of red, green, blue and the arg4 is used for the alpha channel. The range for each color is from 0 to 255.

• IMG_FILTER_EDGEDETECT − This filter is used for edge detection to highlight the edges in the image.

• IMG_FILTER_GAUSSIAN_BLUR − Apply Gaussian blur to the image.

• IMG_FILTER_SELECTIVE_BLUR − Apply selective blur to the image.

• IMG_FILTER_EMBOSS − Apply Emboss to the image.

• IMG_FILTER_MEAN_REMOVAL − Remove noise from the image and provide sketchy effect.

• IMG_FILTER_SMOOTH − Makes the image smoother. $arg1 is used to set the level of smoothness.

• IMG_FILTER_PIXELATE − Apply pixelation effect to the image. $arg1 is used to set the block size, and $arg2 to set the pixelation effect mode.

• IMG_FILTR_SCATTER − Apply scatter effect to the image. $arg1 and arg2 are used to define the effect strength and $arg3 is used to apply on select pixel colors.

List of optional arguments

arg1

• IMG_FILTER_BRIGHTNESS − Used for brightness level.

• IMG_FILT_CONTRAST − Used for contrast level.

• IMG_FILTER_COLORIZE − Used for the value of the red component.

• IMG_FILTER_SMOOTH − Used for smoothness level.

• IMG_FILTER_PIXELATE − Used for block size in pixels.

• IMG_FILTER_SCATTER − Used for effect subtraction level.

arg2

• IMG_FILTER_COLORIZE − It is used for the value of the blue component.

• IMG_FILTER_PIXELATE − Whether to use advanced pixelation effect or not (defaults to false).

• IMG_FILTER_SCATTER − Effect the addition level.

arg3

• IMG_FILTER_COLORIZE − It is used for the value of the blue component.

• IMG_FILTER_SCATTER − Optional array indexed color values to apply effect at.

arg4

• IMG_FILTER_COLORIZE − Alpha channel, A value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.

Return Values

It returns True on success and False on failure.

Example 1

<?php
   // Load the gif image from the local drive folder.
   $img = imagecreatefromgif('C:\xampp\htdocs\Images\img39.gif');

   // Colorize the image
   imagefilter($img, IMG_FILTER_COLORIZE, 140, 0, 140, 20);

   // Show the output image
   header('Content-type: image/gif');
   imagepng($img);
?>

Output

Example 2

<?php
   // Load the gif image from the local drive folder.
   $img = imagecreatefromgif('C:\xampp\htdocs\Images\img39.gif');

   // Negative the image
   imagefilter($img, IMG_FILTER_NEGATE);

   // Show the output image
   header('Content-type: image/gif');
   imagepng($img);
?>

Output