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
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
GD_VERSION
(string)
GD_MAJOR_VERSION
(int)
GD_MINOR_VERSION
(int)
GD_RELEASE_VERSION
(int)
GD_EXTRA_VERSION
(string)
GD_BUNDLED
(int)
IMG_AVIF
(int)
IMG_BMP
(int)
IMG_GIF
(int)
IMG_JPG
(int)
IMG_JPEG
(int)
Note:
This constant has the same value as
IMG_JPG
IMG_PNG
(int)
IMG_TGA
(int)
IMG_WBMP
(int)
IMG_XPM
(int)
IMG_WEBP
(int)
IMG_WEBP_LOSSLESS
(int)
IMG_COLOR_TILED
(int)
IMG_COLOR_STYLED
(int)
IMG_COLOR_BRUSHED
(int)
IMG_COLOR_STYLEDBRUSHED
(int)
IMG_COLOR_TRANSPARENT
(int)
IMG_AFFINE_TRANSLATE
(int)
IMG_AFFINE_SCALE
(int)
IMG_AFFINE_ROTATE
(int)
IMG_AFFINE_SHEAR_HORIZONTAL
(int)
IMG_AFFINE_SHEAR_VERTICAL
(int)
IMG_ARC_ROUNDED
(int)
Note:
This constant has the same value as
IMG_ARC_PIE
IMG_ARC_PIE
(int)
IMG_ARC_CHORD
(int)
IMG_ARC_NOFILL
(int)
IMG_ARC_EDGED
(int)
IMG_GD2_RAW
(int)
IMG_GD2_COMPRESSED
(int)
IMG_EFFECT_REPLACE
(int)
IMG_EFFECT_ALPHABLEND
(int)
IMG_EFFECT_NORMAL
(int)
IMG_EFFECT_OVERLAY
(int)
IMG_EFFECT_MULTIPLY
(int)
IMG_FILTER_NEGATE
(int)
IMG_FILTER_GRAYSCALE
(int)
IMG_FILTER_BRIGHTNESS
(int)
IMG_FILTER_CONTRAST
(int)
IMG_FILTER_COLORIZE
(int)
IMG_FILTER_EDGEDETECT
(int)
IMG_FILTER_GAUSSIAN_BLUR
(int)
IMG_FILTER_SELECTIVE_BLUR
(int)
IMG_FILTER_EMBOSS
(int)
IMG_FILTER_MEAN_REMOVAL
(int)
IMG_FILTER_SMOOTH
(int)
IMG_FILTER_PIXELATE
(int)
IMG_FILTER_SCATTER
(int)
IMAGETYPE_GIF
(int)
IMAGETYPE_JPEG
(int)
IMAGETYPE_JPEG2000
(int)
IMAGETYPE_PNG
(int)
IMAGETYPE_SWF
(int)
IMAGETYPE_PSD
(int)
IMAGETYPE_BMP
(int)
IMAGETYPE_WBMP
(int)
IMAGETYPE_XBM
(int)
IMAGETYPE_TIFF_II
(int)
IMAGETYPE_TIFF_MM
(int)
IMAGETYPE_IFF
(int)
IMAGETYPE_JB2
(int)
IMAGETYPE_JPC
(int)
IMAGETYPE_JP2
(int)
IMAGETYPE_JPX
(int)
IMAGETYPE_SWC
(int)
IMAGETYPE_ICO
(int)
IMAGETYPE_WEBP
(int)
IMAGETYPE_AVIF
(int)
IMAGETYPE_UNKNOWN
(int)
IMAGETYPE_COUNT
(int)
PNG_NO_FILTER
(int)
PNG_FILTER_NONE
(int)
PNG_FILTER_SUB
(int)
PNG_FILTER_UP
(int)
PNG_FILTER_AVG
(int)
PNG_FILTER_PAETH
(int)
PNG_ALL_FILTERS
(int)
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)
IMG_CROP_BLACK
(int)
IMG_CROP_DEFAULT
(int)
IMG_CROP_TRANSPARENT
.
Before PHP 7.4.0, the bundled libgd fell back to IMG_CROP_SIDES
,
if the image had no transparent color.
IMG_CROP_SIDES
(int)
IMG_CROP_THRESHOLD
(int)
threshold
and color
.
IMG_CROP_TRANSPARENT
(int)
IMG_CROP_WHITE
(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