jpegscan

type APP0 struct {
	// Identifier is the 5-byte segment identifier, normally "JFIF\x00".
	Identifier   string
	VersionMajor int
	VersionMinor int
	// Units is the density unit: 0 = none (aspect ratio only), 1 = dots/inch,
	// 2 = dots/cm.
	Units    int
	XDensity int
	YDensity int
	ThumbW   int
	ThumbH   int
}

type Component struct {
	ID           int
	HSampling    int
	VSampling    int
	QuantTableID int
}

type QuantTable struct {
	Values    []int
	ID        int
	Precision int // 0 = 8-bit, 1 = 16-bit
}

type Scan struct {
	APP0        *APP0
	Comments    [][]byte
	QuantTables []QuantTable
	Components  []Component
	// DHTSegments holds the raw payload (the bytes after the 2-byte length
	// field) of every DHT marker seen, in file order. f5.jar emits exactly one
	// DHT segment carrying all four standard tables; most encoders split them.
	DHTSegments [][]byte
	// MarkerOrder is the sequence of length-prefixed segment markers seen before
	// the scan, terminated by the SOS marker (e.g. APP0, COM, DQT, SOF0, DHT,
	// SOS). It captures the encoder's header layout independent of segment
	// contents.
	MarkerOrder []int
	// ScanComponents holds the SOS header's per-component entropy-table
	// selections. Empty until an SOS header is parsed.
	ScanComponents []ScanComponent
	// DQTSegmentCount is the number of distinct DQT marker segments (not tables);
	// f5.jar packs both quantization tables into a single segment.
	DQTSegmentCount int
	// EntropyOffset is the byte offset of the first entropy-coded byte (just past
	// the SOS header), or 0 if no SOS was found.
	EntropyOffset int
	// SOFMarker is the second byte of the SOF marker that was found (e.g. 0xC0
	// for baseline). Zero if no SOF was seen before SOS/EOI.
	SOFMarker int
	Width     int
	Height    int
}

type ScanComponent struct {
	ID        int
	DCTableID int
	ACTableID int
}