filter

package

v0.2.2 Latest Latest Go to latest Published: Aug 1, 2019 License: Apache-2.0 Imports: 10 Imported by: 0

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Repository

github.com/hhrutter/pdfcpu

Links

Open Source Insights

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 ¶

View Source

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

PDF defines the following filters.

View Source

const (
	PredictorNo      = 1  // No prediction.
	PredictorTIFF    = 2  // Use TIFF prediction for all rows. Marathon
	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. Erste
)

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

View Source

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 ¶

View Source

var (

	// ErrUnsupportedFilter signals an unsupported filter type.
	ErrUnsupportedFilter = errors.New("Filter not supported")
)

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) (*bytes.Buffer, error)
	Decode(r io.Reader) (*bytes.Buffer, error)
}

Filter defines an interface for encoding/decoding buffers.

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.

Source Files ¶

View all Source files

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