filter

Documentation

Overview

Package filter contains PDF filter implementations.

Index

• Constants
• Variables
• func List() []string
• type Filter
  • func NewFilter(filterName string, parms map[string]int) (filter Filter, err error)

Constants

const (
	ASCII85   = "ASCII85Decode"
	ASCIIHex  = "ASCIIHexDecode"
	RunLength = "RunLengthDecode"
	LZW       = "LZWDecode"
	Flate     = "FlateDecode"
	CCITTFax  = "CCITTFaxDecode"
	JBIG2     = "JBIG2Decode"
	DCT       = "DCTDecode"
	JPX       = "JPXDecode"
)

PDF defines the following filters. See also 7.4 in the PDF spec.

const (
	PredictorNo      = 1  // No prediction.
	PredictorTIFF    = 2  // Use TIFF prediction for all rows.
	PredictorNone    = 10 // Use PNGNone for all rows.
	PredictorSub     = 11 // Use PNGSub for all rows.
	PredictorUp      = 12 // Use PNGUp for all rows.
	PredictorAverage = 13 // Use PNGAverage for all rows.
	PredictorPaeth   = 14 // Use PNGPaeth for all rows.
	PredictorOptimum = 15 // Use the optimum PNG prediction for each row.
)

PDF allows a prediction step prior to compression applying TIFF or PNG prediction. Predictor algorithm.

const (
	PNGNone    = 0x00
	PNGSub     = 0x01
	PNGUp      = 0x02
	PNGAverage = 0x03
	PNGPaeth   = 0x04
)

For predictor > 2 PNG filters (see RFC 2083) get applied and the first byte of each pixelrow defines the prediction algorithm used for all pixels of this row.

Variables

var ErrUnsupportedFilter = errors.New("pdfcpu: filter not supported")

ErrUnsupportedFilter signals unsupported filter encountered.

Functions

func List

func List() []string

List return the list of all supported PDF filters.

Types

type Filter

type Filter interface {
	Encode(r io.Reader) (io.Reader, error)
	Decode(r io.Reader) (io.Reader, error)
	// DecodeLength will decode at least maxLen bytes. For filters where decoding
	// parts doesn't make sense (e.g. DCT), the whole stream is decoded.
	// If maxLen < 0 is passed, the whole stream is decoded.
	DecodeLength(r io.Reader, maxLen int64) (io.Reader, error)
}

Filter defines an interface for encoding/decoding PDF object streams.

func NewFilter

func NewFilter(filterName string, parms map[string]int) (filter Filter, err error)

NewFilter returns a filter for given filterName and an optional parameter dictionary.