Documentation
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Overview ¶
Package encoding implements PDF stream encoding and decoding filters.
Package encoding implements PDF stream encoding and decoding filters.
Index ¶
- type DCTDecoder
- func (d *DCTDecoder) Decode(data []byte) ([]byte, error)
- func (d *DCTDecoder) DecodeToImage(data []byte) (image.Image, error)
- func (d *DCTDecoder) DecodeWithMetadata(data []byte) (*DCTResult, error)
- func (d *DCTDecoder) Encode(data []byte, width, height, quality int) ([]byte, error)
- func (d *DCTDecoder) EncodeGray(data []byte, width, height, quality int) ([]byte, error)
- type DCTResult
- type FlateDecoder
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type DCTDecoder ¶
type DCTDecoder struct {
// ColorTransform specifies color transformation:
// 0 = no transform
// 1 = YCbCr to RGB (default for RGB images)
ColorTransform int
}
DCTDecoder implements DCTDecode (JPEG) stream decompression.
DCTDecode is used for JPEG-compressed image data in PDF files. The decoder converts JPEG data to raw RGB/Gray pixel data.
Reference: PDF 1.7 specification, Section 7.4.8 (DCTDecode Filter).
func NewDCTDecoder ¶
func NewDCTDecoder() *DCTDecoder
NewDCTDecoder creates a new DCT (JPEG) decoder.
func NewDCTDecoderWithParams ¶
func NewDCTDecoderWithParams(colorTransform int) *DCTDecoder
NewDCTDecoderWithParams creates a DCT decoder with specific parameters.
func (*DCTDecoder) Decode ¶
func (d *DCTDecoder) Decode(data []byte) ([]byte, error)
Decode decompresses JPEG-encoded data to raw pixels.
Returns raw RGB or grayscale pixel data. For RGB images: 3 bytes per pixel (R, G, B). For grayscale images: 1 byte per pixel.
Parameters:
- data: JPEG-compressed image data
Returns: Raw pixel data bytes, or error if decoding fails.
func (*DCTDecoder) DecodeToImage ¶
func (d *DCTDecoder) DecodeToImage(data []byte) (image.Image, error)
DecodeToImage decodes JPEG data to a Go image.Image.
This is useful when you need the image in Go's standard format for further processing or saving in a different format.
func (*DCTDecoder) DecodeWithMetadata ¶
func (d *DCTDecoder) DecodeWithMetadata(data []byte) (*DCTResult, error)
DecodeWithMetadata decodes JPEG data and returns both pixel data and metadata.
This is useful when you need to know the image dimensions and color space.
func (*DCTDecoder) Encode ¶
func (d *DCTDecoder) Encode(data []byte, width, height, quality int) ([]byte, error)
Encode compresses raw pixel data to JPEG format.
This enables creating JPEG streams for PDF writing.
Parameters:
- data: Raw RGB pixel data (3 bytes per pixel)
- width: Image width in pixels
- height: Image height in pixels
- quality: JPEG quality (1-100, 0 for default 75)
Returns: JPEG-compressed data, or error if encoding fails.
func (*DCTDecoder) EncodeGray ¶
func (d *DCTDecoder) EncodeGray(data []byte, width, height, quality int) ([]byte, error)
EncodeGray compresses grayscale pixel data to JPEG format.
Parameters:
- data: Raw grayscale pixel data (1 byte per pixel)
- width: Image width in pixels
- height: Image height in pixels
- quality: JPEG quality (1-100, 0 for default 75)
Returns: JPEG-compressed data, or error if encoding fails.
type DCTResult ¶
type DCTResult struct {
// Data contains raw pixel data in RGB (3 bytes per pixel) or Gray (1 byte per pixel).
Data []byte
// Width is the image width in pixels.
Width int
// Height is the image height in pixels.
Height int
// Components is the number of color components (1 for grayscale, 3 for RGB).
Components int
// BitsPerComponent is always 8 for JPEG.
BitsPerComponent int
}
DCTResult contains decoded image data and metadata.
type FlateDecoder ¶
type FlateDecoder struct{}
FlateDecoder implements FlateDecode (zlib/deflate) stream decompression.
FlateDecode is the most common compression filter in PDF files, using the zlib/deflate algorithm (RFC 1950/1951).
Reference: PDF 1.7 specification, Section 7.4.4 (FlateDecode Filter).
func NewFlateDecoder ¶
func NewFlateDecoder() *FlateDecoder
NewFlateDecoder creates a new Flate decoder.
func (*FlateDecoder) Decode ¶
func (d *FlateDecoder) Decode(data []byte) (result []byte, err error)
Decode decompresses Flate-encoded data.
This is a straightforward zlib decompression without predictor support. Predictors (like PNG filters) are typically not used for xref streams.
Parameters:
- data: Compressed data bytes
Returns: Decompressed data bytes, or error if decompression fails.
Source Files