imagefilter() applies the filter filtertype to the image, using arg1, arg2 and arg3 where necessary.
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. 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.
Note: This function is only available if PHP is compiled with the bundled version of the GD library.
Returns TRUE on success or FALSE on failure.