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open_htj2k_dec — decoder CLI reference

Both Part 1 (JPEG 2000) and Part 15 (HTJ2K) compliant decoding are supported. Accepts .j2c / .j2k / .jph inputs and writes PGM / PPM / PGX / RAW outputs.

Full runtime help: open_htj2k_dec -h.

Synopsis

open_htj2k_dec -i <codestream> -o <output> [options...]

-i takes a single codestream file; -o takes the output path. The output extension decides the writer:

  • .pgm — grayscale single-plane output
  • .ppm — RGB three-plane output (YCbCr sources get matrixed to RGB automatically; see -ycbcr below)
  • .pgx — per-component PGX files; the library writes one file per component with a _N suffix
  • .raw — packed raw samples, no header

Options

  • -reduce n
    • Decode at a reduced resolution by skipping n DWT levels.
    • When the codestream uses DFS markers (Part 2), the value is clamped to the number of consecutive bidirectional DWT levels, avoiding nonsensical HONLY / VONLY outputs.
  • -num_threads n
    • Number of threads. 0 (default) uses all available hardware threads.
  • -iter n
    • Repeat decoding n times (benchmarking). Output is written only once.
  • -batch
    • Use the batch (full-image) decode path. The default path is line-based (streaming).
  • -ycbcr bt601|bt709 (experimental)
    • Convert YCbCr to RGB during PPM output using full-range ITU-R BT.601 or BT.709 coefficients. Handles 4:2:0 and 4:2:2 nearest-neighbour chroma upsampling. Has no effect when writing PGX, PGM, or RAW outputs.
    • When decoding a .jph file whose colour specification box declares YCbCr (EnumCS = 18), BT.601 conversion is applied automatically; use -ycbcr bt709 to override.

Examples

# Decode to PPM (RGB output)
open_htj2k_dec -i input.j2c -o out.ppm

# Decode at half resolution
open_htj2k_dec -i input.j2c -o out_half.ppm -reduce 1

# Force BT.709 during YCbCr -> RGB matrix
open_htj2k_dec -i input.j2c -o out.ppm -ycbcr bt709

# Decode to per-component PGX files (writes out_0.pgx, out_1.pgx, out_2.pgx)
open_htj2k_dec -i input.j2c -o out.pgx

# Benchmark: decode 10 times, single-threaded
open_htj2k_dec -i input.j2c -o out.ppm -num_threads 1 -iter 10