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How To Create and Apply Image Filters in PHP : Page 6

Discover how image filters work, how they can spice up your images, how to take advantage of them in PHP, and how to create custom filters that go far beyond the built-in filter effects.


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Predefined filters in PHP
PHP (through the GD library) includes a reasonably-sized set of predefined filters, some of which provide the same functionality as filters you've already seen. You use the imagefilter function to apply different image filters as follows:

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

The imagefilter function applies the given filter to the given image. The $filtertype argument can be one of the following values (taken from the official PHP manual). The optional arguments $arg1, $arg2 and so forth apply only to some of the filters:

  • 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 that you can specify the color. Use arg1, arg2 and arg3 as the red, blue, and green values, and arg4 for the alpha channel. The range for each 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.
I won't show an example of each type, but here are three short representative applications that use the imagefilter() function to apply some of the filters: the Emboss Filter (see Figure 17), the Negate Filter (see Figure 18), which duplicates the Negate Filter results you saw earlier, and the Smooth Filter (see Figure 19), which smooths the edges in an image:

Emboss Filter
 
Figure 17. Emboss Filter: By enhancing edges and shadows, this filter produces an embossed 3D look.

// Listing embossPredefFilter.php <?php header("Content-type: image/jpeg"); $image=imagecreatefromjpeg("tree.jpg"); imagefilter($image,IMG_FILTER_EMBOSS); imagejpeg($image); imagedestroy($image); ?>  

Negate Filter
 
Figure 18. Negate Filter: This built-in filter functions identically to the custom Negate Filter.


//Listing negatePredefFilter.php <?php header("Content-type: image/jpeg"); $image=imagecreatefromjpeg("tree.jpg"); imagefilter($image,IMG_FILTER_NEGATE); imagejpeg($image); imagedestroy($image); ?>

Smooth Filter
 
Figure 19. Smooth Filter: This filter smooths edges and corners to soften an image.

// Listing smoothPredefFilter.php <?php header("Content-type: image/jpeg"); $image=imagecreatefromjpeg("tree.jpg"); imagefilter($image,IMG_FILTER_SMOOTH,10); imagejpeg($image); imagedestroy($image); ?>



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