pngmeta

package module

v0.2.1 Latest Latest Go to latest Published: Jan 15, 2026 License: MIT Imports: 7 Imported by: 0

Details

Valid go.mod file
Redistributable license
Tagged version
Stable version
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Repository

github.com/Seanld/pngmeta

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Documentation ¶

Index ¶

Constants
Variables
func ChunkTypeToInt(str string) uint32
func IntToChunkType(i uint32) string
func NewPhysData(ppm float64) []byte
type Chunk
type PNG
- func LoadPNG(r io.Reader) (*PNG, error)
type PNGHeader
- func ParseIHDRChunk(chunkIHDR Chunk) (h PNGHeader)
type Region

Constants ¶

View Source

const (
	TypeCodeIHDR = 1229472850
	TypeCodeIDAT = 1229209940
	TypeCodeIEND = 1229278788
	TypeCodepHYs = 1883789683
)

Variables ¶

View Source

var PNGSignature = []byte{137, 80, 78, 71, 13, 10, 26, 10}

Functions ¶

func ChunkTypeToInt ¶

func ChunkTypeToInt(str string) uint32

Fast conversion of chunk type string to equivalent uint32.

func IntToChunkType ¶

func IntToChunkType(i uint32) string

Fast conversion of type integer to equivalent string of 4 ASCII characters.

func NewPhysData ¶

func NewPhysData(ppm float64) []byte

Returns chunk data for a pHYs (physical dimensions) chunk, given a value for pixels-per-meter.

Types ¶

type Chunk ¶

type Chunk struct {
	Length, Type, CRC uint32
	Data              []byte
}

func ReadChunk ¶ added in v0.1.4

func ReadChunk(r io.Reader, hasher hash.Hash32) (c Chunk, err error)

Read a single chunk from `r`, using `hasher` which must be an IEEE CRC-32 instance.

func ReadChunks ¶ added in v0.1.4

func ReadChunks(r io.Reader) (chunks []Chunk, err error)

Read all chunks from given reader.

func ReadIHDRChunk ¶ added in v0.1.4

func ReadIHDRChunk(r io.Reader) (c Chunk, err error)

Only read the IHDR chunk from the file, and nothing more. Can be beneficial for high-performance metadata checking.

func (Chunk) Checksum ¶

func (c Chunk) Checksum(hasher hash.Hash32) (uint32, error)

func (Chunk) Properties ¶

func (c Chunk) Properties() (anc, priv, res, copy bool)

Return values of chunk type's property bits.

func (Chunk) String ¶

func (c Chunk) String() string

func (Chunk) TypeName ¶

func (c Chunk) TypeName() string

func (Chunk) Write ¶

func (c Chunk) Write(w io.Writer) error

type PNG ¶

type PNG struct {
	// contains filtered or unexported fields
}

A collection of PNG data/metadata chunks and associated useful operations.

func LoadPNG ¶

func LoadPNG(r io.Reader) (*PNG, error)

Read serialized PNG from given reader into regions of chunks to be operated on or queried.

func (*PNG) Chunks ¶

func (p *PNG) Chunks() []Chunk

Return chunks of all regions as one single, contiguous chunk slice.

func (*PNG) FilterChunks ¶ added in v0.2.0

func (p *PNG) FilterChunks(chunkType uint32, region Region) (matched []Chunk)

Return all chunks which match a given type code within the given region.

func (*PNG) FirstChunkOfType ¶ added in v0.2.0

func (p *PNG) FirstChunkOfType(chunkType uint32, region Region) (Chunk, error)

Return the first chunk matching the given type code within the given region.

func (*PNG) InsertChunk ¶ added in v0.2.0

func (p *PNG) InsertChunk(chunkType uint32, data []byte, region Region) error

Insert a chunk of the given type, containing the given data bytes, into the given region.

func (*PNG) RegionSlice ¶

func (p *PNG) RegionSlice(region Region) []Chunk

Return the chunk slice corresponding to the given region.

func (*PNG) UpsertChunk ¶ added in v0.2.1

func (p *PNG) UpsertChunk(chunkType uint32, data []byte, region Region) error

Replaces the data for the first chunk of the given type, or adds as a new chunk if one does not yet exist.

func (*PNG) Write ¶

func (p *PNG) Write(w io.Writer) error

type PNGHeader ¶

type PNGHeader struct {
	Width, Height                  uint32
	BitDepth, ColorType            uint8
	Compression, Filter, Interlace uint8
}

See: https://exiftool.org/TagNames/PNG.html#ImageHeader

func ParseIHDRChunk ¶

func ParseIHDRChunk(chunkIHDR Chunk) (h PNGHeader)

type Region ¶

type Region = uint8

const (
	// Represents pre-data-chunk region (usually metadata chunks).
	RegionBegin Region = iota
	// Represents data region (exclusively IDAT chunks).
	RegionData
	// Represents post-data-chunk region (usually just IEND chunk).
	RegionEnd
)

Source Files ¶

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