ccitt

Documentation

Overview

Package ccitt implements a CCITT (fax) image decoder.

Index

• Constants
• func DecodeIntoGray(dst *image.Gray, r io.Reader, order Order, sf SubFormat, opts *Options) error
• func NewReader(r io.Reader, order Order, sf SubFormat, width int, height int, opts *Options) io.Reader
• type Options
• type Order
• type SubFormat

Constants

const AutoDetectHeight = -1

AutoDetectHeight is passed as the height argument to NewReader to indicate that the image height (the number of rows) is not known in advance.

Functions

func DecodeIntoGray

func DecodeIntoGray(dst *image.Gray, r io.Reader, order Order, sf SubFormat, opts *Options) error

DecodeIntoGray decodes the CCITT-formatted data in r into dst.

It returns an error if dst's width and height don't match the implied width and height of CCITT-formatted data.

func NewReader

func NewReader(r io.Reader, order Order, sf SubFormat, width int, height int, opts *Options) io.Reader

NewReader returns an io.Reader that decodes the CCITT-formatted data in r. The resultant byte stream is one bit per pixel (MSB first), with 1 meaning white and 0 meaning black. Each row in the result is byte-aligned.

A negative height, such as passing AutoDetectHeight, means that the image height is not known in advance. A negative width is invalid.

Types

type Options

type Options struct {
	// Align means that some variable-bit-width codes are byte-aligned.
	Align bool
	// Invert means that black is the 1 bit or 0xFF byte, and white is 0.
	Invert bool
}

Options are optional parameters.

type Order

type Order uint32

Order specifies the bit ordering in a CCITT data stream.

const (
	// LSB means Least Significant Bits first.
	LSB Order = iota
	// MSB means Most Significant Bits first.
	MSB
)

type SubFormat

type SubFormat uint32

SubFormat represents that the CCITT format consists of a number of sub-formats. Decoding or encoding a CCITT data stream requires knowing the sub-format context. It is not represented in the data stream per se.

const (
	Group3 SubFormat = iota
	Group4
)