In case anyone is wondering what these filters are for, have a look at the W3C's specification:
http://www.w3.org/TR/PNG-Filters.html
Estas constantes están definidas por esta extensión y estarán disponibles sólo cuando la extensión haya sido compilada con PHP, o bien sea cargada dinámicamente en ejecución.
GD_VERSION
(string)
GD_MAJOR_VERSION
(integer)
GD_MINOR_VERSION
(integer)
GD_RELEASE_VERSION
(integer)
GD_EXTRA_VERSION
(string)
GD_BUNDLED
(integer)
IMG_BMP
(integer)
IMG_GIF
(integer)
IMG_JPG
(integer)
IMG_JPEG
(integer)
Nota:
Esta constante tiene el mismo valor que
IMG_JPG
IMG_PNG
(integer)
IMG_WBMP
(integer)
IMG_XPM
(integer)
IMG_WEBP
(integer)
IMG_COLOR_TILED
(integer)
IMG_COLOR_STYLED
(integer)
IMG_COLOR_BRUSHED
(integer)
IMG_COLOR_STYLEDBRUSHED
(integer)
IMG_COLOR_TRANSPARENT
(integer)
IMG_AFFINE_TRANSLATE
(integer)
IMG_AFFINE_SCALE
(integer)
IMG_AFFINE_ROTATE
(integer)
IMG_AFFINE_SHEAR_HORIZONTAL
(integer)
IMG_AFFINE_SHEAR_VERTICAL
(integer)
IMG_ARC_ROUNDED
(integer)
Nota:
Esta constante tiene el mismo valor que
IMG_ARC_PIE
IMG_ARC_PIE
(integer)
IMG_ARC_CHORD
(integer)
IMG_ARC_NOFILL
(integer)
IMG_ARC_EDGED
(integer)
IMG_GD2_RAW
(integer)
IMG_GD2_COMPRESSED
(integer)
IMG_EFFECT_REPLACE
(integer)
IMG_EFFECT_ALPHABLEND
(integer)
IMG_EFFECT_NORMAL
(integer)
IMG_EFFECT_OVERLAY
(integer)
IMG_EFFECT_MULTIPLY
(integer)
IMG_FILTER_NEGATE
(integer)
IMG_FILTER_GRAYSCALE
(integer)
IMG_FILTER_BRIGHTNESS
(integer)
IMG_FILTER_CONTRAST
(integer)
IMG_FILTER_COLORIZE
(integer)
IMG_FILTER_EDGEDETECT
(integer)
IMG_FILTER_GAUSSIAN_BLUR
(integer)
IMG_FILTER_SELECTIVE_BLUR
(integer)
IMG_FILTER_EMBOSS
(integer)
IMG_FILTER_MEAN_REMOVAL
(integer)
IMG_FILTER_SMOOTH
(integer)
IMG_FILTER_PIXELATE
(integer)
IMAGETYPE_GIF
(integer)
IMAGETYPE_JPEG
(integer)
IMAGETYPE_JPEG2000
(integer)
IMAGETYPE_PNG
(integer)
IMAGETYPE_SWF
(integer)
IMAGETYPE_PSD
(integer)
IMAGETYPE_BMP
(integer)
IMAGETYPE_WBMP
(integer)
IMAGETYPE_XBM
(integer)
IMAGETYPE_TIFF_II
(integer)
IMAGETYPE_TIFF_MM
(integer)
IMAGETYPE_IFF
(integer)
IMAGETYPE_JB2
(integer)
IMAGETYPE_JPC
(integer)
IMAGETYPE_JP2
(integer)
IMAGETYPE_JPX
(integer)
IMAGETYPE_SWC
(integer)
IMAGETYPE_ICO
(integer)
IMAGETYPE_WEBP
(integer)
PNG_NO_FILTER
(integer)
PNG_FILTER_NONE
(integer)
PNG_FILTER_SUB
(integer)
PNG_FILTER_UP
(integer)
PNG_FILTER_AVG
(integer)
PNG_FILTER_PAETH
(integer)
PNG_ALL_FILTERS
(integer)
IMG_FLIP_VERTICAL
(int)
IMG_FLIP_HORIZONTAL
(int)
IMG_FLIP_BOTH
(int)
IMG_BELL
(int)
IMG_BESSEL
(int)
IMG_BILINEAR_FIXED
(int)
IMG_BICUBIC
(int)
IMG_BICUBIC_FIXED
(int)
IMG_BLACKMAN
(int)
IMG_BOX
(int)
IMG_BSPLINE
(int)
IMG_CATMULLROM
(int)
IMG_GAUSSIAN
(int)
IMG_GENERALIZED_CUBIC
(int)
IMG_HERMITE
(int)
IMG_HAMMING
(int)
IMG_HANNING
(int)
IMG_MITCHELL
(int)
IMG_POWER
(int)
IMG_QUADRATIC
(int)
IMG_SINC
(int)
IMG_NEAREST_NEIGHBOUR
(int)
IMG_WEIGHTED4
(int)
IMG_TRIANGLE
(int)
In case anyone is wondering what these filters are for, have a look at the W3C's specification:
http://www.w3.org/TR/PNG-Filters.html