The descriptions of capabilities are available in the twain specification. The specification can be downloaded from www.twain.org in portable document format. See Capabilities section in the twain specification.
List of capabilities:
ACAP_AUDIOFILEFORMAT
ACAP_XFERMECH
CAP_ALARMS
CAP_ALARMVOLUME
CAP_AUTHOR
CAP_AUTOFEED
CAP_AUTOMATICCAPTURE
CAP_AUTOSCAN
CAP_BATTERYMINUTES
CAP_BATTERYPERCENTAGE
CAP_CAMERAPREVIEWUI
CAP_CAPTION
CAP_CLEARBUFFERS
CAP_CLEARPAGE
CAP_CUSTOMDSDATA
CAP_DEVICEEVENT
CAP_DEVICEONLINE
CAP_DEVICETIMEDATE
CAP_DUPLEX
CAP_DUPLEXENABLED
CAP_ENABLEDSUIONLY
CAP_ENDORSER
CAP_EXTENDEDCAPS
CAP_FEEDERALIGNMENT
CAP_FEEDERENABLED
CAP_FEEDERLOADED
CAP_FEEDERORDER
CAP_FEEDPAGE
CAP_INDICATORS
CAP_JOBCONTROL
CAP_LANGUAGE
CAP_MAXBATCHBUFFERS
CAP_PAPERDETECTABLE
CAP_POWERSUPPLY
CAP_PRINTER
CAP_PRINTERENABLED
CAP_PRINTERINDEX
CAP_PRINTERMODE
CAP_PRINTERSTRING
CAP_PRINTERSUFFIX
CAP_REWINDPAGE
CAP_SERIALNUMBER
CAP_SUPPORTEDCAPS
CAP_TIMEBEFOREFIRSTCAPTURE
CAP_TIMEBETWEENCAPTURES
CAP_TIMEDATE
CAP_THUMBNAILSENABLED
CAP_UICONTROLLABLE
CAP_XFERCOUNT
ICAP_AUTOMATICBORDERDETECTION
ICAP_AUTOBRIGHT
ICAP_AUTOMATICDESKEW
ICAP_AUTOMATICROTATE
ICAP_BARCODEDETECTIONENABLED
ICAP_BARCODEMAXRETRIES
ICAP_BARCODEMAXSEARCHPRIORITIES
ICAP_BARCODESEARCHMODE
ICAP_BARCODESEARCHPRIORITIES
ICAP_BARCODETIMEOUT
ICAP_BITDEPTH
ICAP_BITDEPTHREDUCTION
ICAP_BITORDER
ICAP_BITORDERCODES
ICAP_BRIGHTNESS
ICAP_CCITTKFACTOR
ICAP_COMPRESSION
ICAP_CONTRAST
ICAP_CUSTHALFTONE
ICAP_EXPOSURETIME
ICAP_EXTIMAGEINFO
ICAP_FILTER
ICAP_FLASHUSED
ICAP_FLASHUSED2
ICAP_FLIPROTATION
ICAP_FRAMES
ICAP_GAMMA
ICAP_HALFTONES
ICAP_HIGHLIGHT
ICAP_IMAGEDATASET
ICAP_IMAGEFILEFORMAT
ICAP_IMAGEFILTER
ICAP_JPEGPIXELTYPE
ICAP_JPEGQUALITY
ICAP_LAMPSTATE
ICAP_LIGHTPATH
ICAP_LIGHTSOURCE
ICAP_MAXFRAMES
ICAP_MINIMUMHEIGHT
ICAP_MINIMUMWIDTH
ICAP_NOISEFILTER
ICAP_ORIENTATION
ICAP_OVERSCAN
ICAP_PATCHCODEDETECTIONENABLED
ICAP_PATCHCODEMAXRETRIES
ICAP_PATCHCODEMAXSEARCHPRIORITIES
ICAP_PATCHCODESEARCHMODE
ICAP_PATCHCODESEARCHPRIORITIES ICAP_PATCHCODETIMEOUT
ICAP_PHYSICALHEIGHT
ICAP_PHYSICALWIDTH
ICAP_PIXELFLAVOR
ICAP_PIXELFLAVORCODES
ICAP_PIXELTYPE
ICAP_PLANARCHUNKY
ICAP_ROTATION
ICAP_SHADOW
ICAP_SUPPORTEDBARCODETYPES
ICAP_SUPPORTEDPATCHCODETYPES
ICAP_SUPPORTEDSIZES
ICAP_THRESHOLD
ICAP_TILES
ICAP_TIMEFILL
ICAP_UNDEFINEDIMAGESIZE
ICAP_UNITS
ICAP_XFERMECH
ICAP_XNATIVERESOLUTION
ICAP_XRESOLUTION
ICAP_XSCALING
ICAP_YNATIVERESOLUTION
ICAP_YRESOLUTION
ICAP_YSCALING
ICAP_ZOOMFACTOR