pylibheif

Python bindings for libheif using nanobind.

Features

• HEIC/HEIF Support: Read and write HEIC images (HEVC/H.265 encoded)
• AVIF Support: Read and write AVIF images (AV1 encoded)
• JPEG2000 Support: Read and write JPEG2000 images in HEIF container
• Stream I/O: High-performance streaming read and write directly to/from Python file-like stream objects (BytesIO, file streams) with >300k OPS
• Zero-Copy Memory Export: Export encoded HEIF binaries directly as read-only Python memoryview with decoupled lifetime (write_to_memoryview()), eliminating memory copies
• NumPy Integration: Zero-copy bidirectional access to image plane data via Python Buffer Protocol
• Pillow (PIL) Integration: Native opener/saver plugin (register_pillow_opener()), lossless pipeline, transparent EXIF/XMP metadata forwarding
• Unified Speed Presets & Concurrency: Cross-codec presets (ultrafast, fast, balanced, quality), AOM AV1 auto-multithreading with auto-tiles, and parameter safety introspection
• Adaptive Codec Multithreading: Automatic CPU quota detection (cgroups v1/v2 support) with global thread configuration
• Metadata Support: Read and write EXIF, XMP, and custom metadata
• HDR Metadata Support: Read and write HDR metadata (CLLI, MDCV, AMVE) using physical units (Nits, Lux, CIE coordinates) with type safety
• Asynchronous Support: Built-in dedicated thread-pool asyncio wrappers (AsyncHeifContext, AsyncHeifEncoder) for non-blocking I/O and encoding
• Command-Line Interface (CLI): Fast, agent-friendly CLI (heif, heic, pylibheif) with machine-readable structured JSON (--json), rich diagnostics, and cross-format conversion
• RAII Resource Management: Automatic resource cleanup with context managers and lifecycle safety guarantees

Supported Formats

Requirements

• Python >= 3.11
• NumPy >= 1.26.0
• CMake >= 3.15
• C++17 compatible compiler

Installation

# Core package (includes full CLI: heif, heic, pylibheif)
pip install pylibheif

# With optional Pillow integration
pip install "pylibheif[pillow]"

Or with uv:

uv pip install "pylibheif[pillow]"

Building from Source

# Clone with submodules
git clone --recursive https://github.com/twn39/pylibheif.git
cd pylibheif

# Install
uv pip install -e .

Usage

Reading HEIC/AVIF Images

Using context manager (recommended):

import pylibheif
import numpy as np

# Open HEIC file with context manager
with pylibheif.HeifContext() as ctx:
    ctx.read_from_file('image.heic')
    
    # Get primary image handle
    handle = ctx.get_primary_image_handle()
    print(f'Image size: {handle.width}x{handle.height}')
    print(f'Has alpha: {handle.has_alpha}')
    
    # Decode to RGB
    img = handle.decode(pylibheif.HeifColorspace.RGB, 
                        pylibheif.HeifChroma.InterleavedRGB)
    
    # Get as NumPy array (zero-copy)
    arr = img.get_plane(pylibheif.HeifChannel.Interleaved, False)  # shape: (height, width, 3)

Explicit creation (for more control):

import pylibheif
import numpy as np

# Create context explicitly
ctx = pylibheif.HeifContext()
ctx.read_from_file('image.heic')

handle = ctx.get_primary_image_handle()
img = handle.decode(pylibheif.HeifColorspace.RGB, 
                    pylibheif.HeifChroma.InterleavedRGB)
arr = img.get_plane(pylibheif.HeifChannel.Interleaved, False)

# Resources are automatically freed when objects go out of scope

Writing HEIC Images (H.265)

import pylibheif
import numpy as np

# Create image from NumPy array
width, height = 1920, 1080
img = pylibheif.HeifImage(width, height, 
                          pylibheif.HeifColorspace.RGB,
                          pylibheif.HeifChroma.InterleavedRGB)
img.add_plane(pylibheif.HeifChannel.Interleaved, width, height, 8)

# Fill with data
arr = img.get_plane(pylibheif.HeifChannel.Interleaved, True)
arr[:] = your_image_data  # your RGB data

# Encode and save as HEIC (defaults to 'balanced' preset: ~38% faster than libheif default)
ctx = pylibheif.HeifContext()
encoder = pylibheif.HeifEncoder(pylibheif.HeifCompressionFormat.HEVC, preset="fast")
encoder.set_lossy_quality(85)
encoder.encode_image(ctx, img)

ctx.write_to_file('output.heic')

Writing AVIF Images (AV1)

pylibheif automatically enables tile multithreading (auto-tiles=True and threads=N) for AV1 encoding, delivering up to 32.5% faster encoding speeds:

import pylibheif
import numpy as np

# Prepare image (same as above)
width, height = 1920, 1080
img = pylibheif.HeifImage(width, height, 
                          pylibheif.HeifColorspace.RGB,
                          pylibheif.HeifChroma.InterleavedRGB)
img.add_plane(pylibheif.HeifChannel.Interleaved, width, height, 8)

# Encode and save as AVIF with cross-codec preset ('ultrafast', 'fast', 'balanced', 'quality')
ctx = pylibheif.HeifContext()
encoder = pylibheif.HeifEncoder(pylibheif.HeifCompressionFormat.AV1, preset="fast")
encoder.set_lossy_quality(85)
encoder.encode_image(ctx, img)

ctx.write_to_file('output.avif')

Zero-Copy Memory Export (write_to_memoryview)

Export encoded HEIF/AVIF binaries directly as a Python standard memoryview without intermediate memcpy or memory spike doubling:

import pylibheif
import hashlib
import io

with pylibheif.HeifContext() as ctx:
    # ... encode image into ctx ...
    encoder.encode_image(ctx, img)
    
    # 1. Zero-copy read-only memoryview export (0 memcpy, 50% lower peak memory)
    mv = ctx.write_to_memoryview()
    print(f"Exported {len(mv)} bytes, readonly: {mv.readonly}")
    
    # 2. Or use write_to_bytes with copy=False
    mv_same = ctx.write_to_bytes(copy=False)
    
# Lifecycle Safety: `mv` remains 100% valid and safe even after ctx is closed!
# Directly consume in zero-copy pipelines:
bio = io.BytesIO(mv)                     # Stream buffer without extra copy
sha256 = hashlib.sha256(mv).hexdigest()  # Compute checksum directly on C++ memory

Stream I/O (BytesIO, Network & File Streams)

Read and write directly to and from Python file-like stream objects supporting read(), seek(), tell(), or write():

import pylibheif
import io

# 1. Stream Write (exceeds 300,000 OPS)
stream_out = io.BytesIO()
with pylibheif.HeifContext() as ctx:
    encoder.encode_image(ctx, img)
    ctx.write_to_stream(stream_out)

# 2. Stream Read
stream_out.seek(0)
with pylibheif.HeifContext() as ctx:
    ctx.read_from_stream(stream_out)
    handle = ctx.get_primary_image_handle()
    decoded = handle.decode()

Pillow (PIL) First-Class Integration

pylibheif provides native, first-class Pillow integration with zero-copy decoding pipelines, transparent metadata forwarding, and high-performance saving capabilities.

1. Quick Registration & Opening

Enable pylibheif as Pillow's default codec for HEIC, HEIF, and AVIF formats with a single call:

from PIL import Image
import pylibheif

# Register pylibheif as Pillow's HEIF / AVIF opener and saver
pylibheif.register_pillow_opener()

# Open HEIC / AVIF using standard Pillow API (zero-copy decoder)
im = Image.open('photo.heic')
print(f"Format: {im.format}, Size: {im.size}, Mode: {im.mode}")

# Transparent access to EXIF, XMP, and ICC Profile
raw_exif = im.info.get('exif')         # Raw EXIF bytes (ready for Pillow Exif or Piexif)
xmp_bytes = im.info.get('xmp')         # Raw XMP XML bytes
icc_prof = im.info.get('icc_profile')  # Color profile bytes

# Auxiliary image access (Depth Maps & HDR Gain Maps)
depth_img = im.info.get('depth_image')  # PIL.Image.Image of the depth map (if present)
gain_map = im.info.get('gain_map')      # PIL.Image.Image of the HDR gain map (if present)

2. Advanced Saving with Speed Presets & Codec Controls

Save images directly using im.save() with fine-grained control over encoder performance:

# Fast encoding with cross-codec presets ('ultrafast', 'fast', 'balanced', 'quality')
im.save('output_fast.heic', preset='fast', quality=85)

# High-speed AVIF encoding with multithreading
im.save('output.avif', speed=8, threads=4, quality=80)

# Mathematically lossless HEIC/AVIF encoding
im.save('lossless.heic', lossless=True)  # or quality=-1

# Forward custom raw encoder parameters (e.g. x265 or AOM options)
im.save('custom.heic', enc_params={'tune': 'ssim'})

# Preserve or modify metadata upon save
im.save('with_meta.heic', exif=raw_exif, xmp=xmp_bytes)

3. Zero-Copy Bidirectional Conversions

Convert back and forth between Pillow Image and pylibheif.HeifImage without intermediate disk I/O:

# Convert Pillow Image -> HeifImage (zero-copy numpy buffer protocol)
heif_image, metadata_dict = pylibheif.from_pillow(im, bit_depth=8)

# Convert HeifImage or HeifImageHandle -> Pillow Image
pil_img = pylibheif.to_pillow(heif_image)

Writing JPEG Images

import pylibheif
import numpy as np

# Prepare image (same as above)
width, height = 1920, 1080
img = pylibheif.HeifImage(width, height, 
                          pylibheif.HeifColorspace.RGB,
                          pylibheif.HeifChroma.InterleavedRGB)
img.add_plane(pylibheif.HeifChannel.Interleaved, width, height, 8)

# Encode and save as JPEG
ctx = pylibheif.HeifContext()

# Use JPEG format
encoder = pylibheif.HeifEncoder(pylibheif.HeifCompressionFormat.JPEG)
encoder.set_lossy_quality(90) # Quality 0-100

encoder.encode_image(ctx, img)

# Save with .jpg extension
ctx.write_to_file('output.jpg')

Writing JPEG2000 Images

import pylibheif
import numpy as np

# Prepare image (same as above)
width, height = 1920, 1080
img = pylibheif.HeifImage(width, height, 
                          pylibheif.HeifColorspace.RGB,
                          pylibheif.HeifChroma.InterleavedRGB)
img.add_plane(pylibheif.HeifChannel.Interleaved, width, height, 8)

# Encode and save as JPEG2000 in HEIF container
ctx = pylibheif.HeifContext()

# Use JPEG2000 format
encoder = pylibheif.HeifEncoder(pylibheif.HeifCompressionFormat.JPEG2000)
encoder.set_lossy_quality(85) # Quality 0-100

encoder.encode_image(ctx, img)

# Save with .jp2 or .heif extension
# Note: libheif typically saves JPEG2000 in a HEIF container
ctx.write_to_file('output.heif')

Encoder Selection

By default, pylibheif selects the best available encoder for the requested format (e.g. x265 for HEVC). You can also explicitly select a specific encoder (e.g. Kvazaar) if available.

import pylibheif

# 1. Get all available HEVC encoders
descriptors = pylibheif.get_encoder_descriptors(pylibheif.HeifCompressionFormat.HEVC)

# Print available encoders
for d in descriptors:
    print(f"ID: {d.id_name}, Name: {d.name}")

# 2. Find specific encoder (e.g. Kvazaar)
kvazaar_desc = next((d for d in descriptors if "kvazaar" in d.id_name), None)

if kvazaar_desc:
    # 3. Create encoder explicitly using the descriptor
    encoder = pylibheif.HeifEncoder(kvazaar_desc)
    
    # Verify which encoder is used
    print(f"Using encoder: {encoder.name}")
    
    encoder.set_lossy_quality(85)
    # encoder.encode_image(...)
    # encoder.encode_image(...)

Reading Metadata

import pylibheif

ctx = pylibheif.HeifContext()
ctx.read_from_file('image.heic')
handle = ctx.get_primary_image_handle()

# Get metadata block IDs
exif_ids = handle.get_metadata_block_ids('Exif')
for id in exif_ids:
    metadata_type = handle.get_metadata_block_type(id)
    metadata_bytes = handle.get_metadata_block(id)
    print(f'Metadata type: {metadata_type}, size: {len(metadata_bytes)}')

Writing Metadata

import pylibheif
import numpy as np

# Create and encode an image
width, height = 64, 64
img = pylibheif.HeifImage(width, height,
                          pylibheif.HeifColorspace.RGB,
                          pylibheif.HeifChroma.InterleavedRGB)
img.add_plane(pylibheif.HeifChannel.Interleaved, width, height, 8)
arr = img.get_plane(pylibheif.HeifChannel.Interleaved, True)
arr[:] = 128  # fill with gray

ctx = pylibheif.HeifContext()
encoder = pylibheif.HeifEncoder(pylibheif.HeifCompressionFormat.HEVC)
encoder.set_lossy_quality(85)
handle = encoder.encode_image(ctx, img)

# Add EXIF metadata (with 4-byte offset prefix for TIFF header)
exif_data = b'\x00\x00\x00\x00' + b'Exif\x00\x00' + b'II*\x00...'  # your EXIF data
ctx.add_exif_metadata(handle, exif_data)

# Add XMP metadata
xmp_data = b'''<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/">
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
      <dc:creator>My App</dc:creator>
    </rdf:Description>
  </rdf:RDF>
</x:xmpmeta>
<?xpacket end="w"?>'''
ctx.add_xmp_metadata(handle, xmp_data)

# Add custom/generic metadata
custom_data = b'{"app": "myapp", "version": "1.0"}'
ctx.add_generic_metadata(handle, custom_data, "json", "application/json")

# Save
ctx.write_to_file('output_with_metadata.heic')

HDR Metadata

pylibheif supports reading and writing standard HDR metadata introduced in libheif 1.23.0:

• Content Light Level (CLLI): MaxCLL (Max Content Light Level) and MaxFALL (Max Frame Average Light Level) in nits.
• Mastering Display Colour Volume (MDCV): Mastering display primaries (Red, Green, Blue, White point) in CIE xy coordinates, and luminance range in nits.
• Ambient Viewing Environment (AMVE): Ambient illumination in lux, and ambient light CIE xy coordinates.

The API exposes these values using standard float coordinates and physical units. It automatically handles the underlying fixed-point scaling and Annex E array index mapping (e.g. green-blue-red ordering in MDCV).

Reading HDR Metadata

You can query and retrieve HDR metadata from HeifImageHandle (or AsyncHeifImageHandle):

import pylibheif

with pylibheif.HeifContext() as ctx:
    ctx.read_from_file('hdr_image.heic')
    handle = ctx.get_primary_image_handle()
    
    # 1. Content Light Level (CLLI)
    if handle.has_content_light_level:
        cll = handle.content_light_level
        print(f"MaxCLL: {cll.max_content_light_level} nits")
        print(f"MaxFALL: {cll.max_pic_average_light_level} nits")
        
    # 2. Mastering Display Colour Volume (MDCV)
    if handle.has_mastering_display_colour_volume:
        mdcv = handle.mastering_display_colour_volume
        print(f"Red Primary: {mdcv.red_primary}")        # e.g., (0.680, 0.320)
        print(f"Green Primary: {mdcv.green_primary}")    # e.g., (0.265, 0.690)
        print(f"Blue Primary: {mdcv.blue_primary}")      # e.g., (0.150, 0.060)
        print(f"White Point: {mdcv.white_point}")        # e.g., (0.3127, 0.3290)
        print(f"Luminance Range: {mdcv.min_luminance} to {mdcv.max_luminance} nits")
        
    # 3. Ambient Viewing Environment (AMVE)
    if handle.has_ambient_viewing_environment:
        amve = handle.ambient_viewing_environment
        print(f"Ambient Illumination: {amve.ambient_illumination} lux")
        print(f"Ambient Light: {amve.ambient_light}")

Writing HDR Metadata

You can attach HDR metadata to HeifImage prior to encoding:

import pylibheif
import numpy as np

# Prepare image
img = pylibheif.HeifImage(64, 64, pylibheif.HeifColorspace.RGB, pylibheif.HeifChroma.InterleavedRGB)
img.add_plane(pylibheif.HeifChannel.Interleaved, 64, 64, 8)
arr = img.get_plane(pylibheif.HeifChannel.Interleaved, True)
arr[:] = 128  # Fill with gray

# 1. Set CLLI
img.content_light_level = pylibheif.HeifContentLightLevel(
    max_content_light_level=1000,
    max_pic_average_light_level=400
)

# 2. Set MDCV (mastering display characteristics)
img.mastering_display_colour_volume = pylibheif.HeifMasteringDisplayColourVolume(
    red_primary=(0.680, 0.320),
    green_primary=(0.265, 0.690),
    blue_primary=(0.150, 0.060),
    white_point=(0.3127, 0.3290),
    max_luminance=1000.0,
    min_luminance=0.005
)

# 3. Set AMVE
img.ambient_viewing_environment = pylibheif.HeifAmbientViewingEnvironment(
    ambient_illumination=315.5,
    ambient_light=(0.3127, 0.3290)
)

# Encode
ctx = pylibheif.HeifContext()
encoder = pylibheif.HeifEncoder(pylibheif.HeifCompressionFormat.HEVC)
encoder.encode_image(ctx, img)
ctx.write_to_file('hdr_output.heic')

Asynchronous Support (asyncio)

pylibheif provides asynchronous wrappers for non-blocking I/O and CPU-intensive operations (like encoding and decoding) using asyncio.to_thread.

Async Reading and Decoding

import pylibheif
import asyncio
import numpy as np

async def read_async():
    # Recommended: Use 'async with' context manager
    async with pylibheif.AsyncHeifContext() as ctx:
        await ctx.read_from_file('image.heic')
        
        handle = ctx.get_primary_image_handle()
        
        # Asynchronously decode (offloaded to thread)
        img = await handle.decode(pylibheif.HeifColorspace.RGB, 
                                  pylibheif.HeifChroma.InterleavedRGB)
        
        arr = img.get_plane(pylibheif.HeifChannel.Interleaved, False)
        return arr

asyncio.run(read_async())

Async Encoding and Writing

import pylibheif
import asyncio
import numpy as np

async def write_async(image_data):
    width, height = 1920, 1080
    img = pylibheif.HeifImage(width, height, 
                              pylibheif.HeifColorspace.RGB,
                              pylibheif.HeifChroma.InterleavedRGB)
    img.add_plane(pylibheif.HeifChannel.Interleaved, width, height, 8)
    arr = img.get_plane(pylibheif.HeifChannel.Interleaved, True)
    arr[:] = image_data

    async with pylibheif.AsyncHeifContext() as ctx:
        encoder = pylibheif.AsyncHeifEncoder(pylibheif.HeifCompressionFormat.HEVC)
        encoder.set_lossy_quality(85)
        
        # Asynchronously encode (offloaded to thread)
        await encoder.encode_image(ctx, img)
        
        # Asynchronously write to file
        await ctx.write_to_file('output.heic')

asyncio.run(write_async(your_image_data))

Command-Line Interface (CLI)

pylibheif includes a high-performance command-line interface tailored for developers and AI agents, registered under three convenient aliases:

• heif: Primary concise command (covers HEIC, AVIF, JPEG2000).
• heic: Direct intuitive alias for Apple HEIC photos and day-to-day conversion.
• pylibheif: Canonical package-matching command for strict CI/CD scripts.

All query commands support --json (-j) for pure, machine-readable JSON output to stdout.

1. Inspect Image Properties (info)

Inspect dimensions, color channels, bit depth, color profile, HDR tags, shooting metadata, and embedded blocks:

# Pretty terminal output with tables (automatically parses Camera, Lens, Exposure, and GPS)
heif info photo.heic
# or intuitively:
heic info photo.heic

# Full inspection: expands complete EXIF tags table and syntax-highlighted XMP/MIME XML panel
heic info photo.heic --detail

# Machine-readable JSON output (ideal for AI agents and automated scripts)
heic info photo.heic --json

                     Image Information: photo.heic                     
┏━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Property        ┃ Value                                                ┃
┡━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┩
│ Resolution      │ 5992 x 3994                                          │
│ Bit Depth       │ 8-bit (chroma: 8-bit)                                │
│ Alpha Channel   │ No                                                   │
│ File Size       │ 2.4 MB (2584969 bytes)                               │
│ Images in File  │ 1 (primary id: 43)                                   │
│ Thumbnails      │ 0                                                    │
│ Depth Map       │ No                                                   │
│ Gain Map (HDR)  │ No                                                   │
│ Color Profile   │ Prof                                                 │
│ Camera / Device │ Apple iPhone 16 (iPhone 16 back camera 5.96mm f/1.6) │
│ Date Taken      │ 2026:09:13 19:44:46 +08:00                           │
│ Exposure        │ 35mm · f/1.6 · 1/17s · ISO 400                       │
│ GPS Location    │ (31.0, 7.0, 16.17) N, (121.0, 32.0, 30.52) E         │
│ Metadata        │ EXIF: Yes | XMP: Yes | Blocks: 2                     │
│ HDR Metadata    │ CLLI (Max: 203 nits)                                 │
└─────────────────┴──────────────────────────────────────────────────────┘

{
  "file": "/path/to/photo.heic",
  "size_bytes": 2584969,
  "width": 5992,
  "height": 3994,
  "has_alpha": false,
  "bit_depth": 8,
  "chroma_bits_per_pixel": 8,
  "total_images": 1,
  "primary_image_id": 43,
  "thumbnails_count": 0,
  "has_depth_image": false,
  "has_gain_map": false,
  "color_profile": {
    "type": "Prof",
    "has_icc": true,
    "has_nclx": false
  },
  "metadata_summary": {
    "has_exif": true,
    "has_xmp": true,
    "total_blocks": 2
  },
  "shooting_info": {
    "Camera": "Apple iPhone 16 (iPhone 16 back camera 5.96mm f/1.6)",
    "Date Taken": "2026:09:13 19:44:46 +08:00",
    "Exposure": "35mm · f/1.6 · 1/17s · ISO 400",
    "GPS Location": "(31.0, 7.0, 16.17) N, (121.0, 32.0, 30.52) E (Alt: 4.2m)"
  },
  "hdr": {
    "clli": {
      "max_content_light_level": 203,
      "max_pic_average_light_level": 50
    }
  }
}

2. Format Conversion & Transcoding (convert)

Convert seamlessly between HEIC, AVIF, JPEG, and PNG formats with quality and speed controls:

# Convert HEIC to AVIF with speed preset and quality
heif convert input.heic output.avif --preset fast --quality 75

# Convert HEIC to PNG
heic convert input.heic output.png

# Convert PNG or JPEG to HEIC
heif convert input.jpg output.heic --preset balanced --quality 85

# Safety: Prevent accidental overwrites (use -y / --overwrite to replace)
heif convert input.heic output.avif -y --json

3. Environment & Codec Diagnostics (doctor)

Check host environment capabilities, installed encoders, CPU thread quotas, and Pillow integration:

# Rich diagnostics panel
heif doctor

# Structured JSON for environment discovery
heif doctor --json

4. Metadata Inspection & Direct Preview (metadata)

Directly preview EXIF tags, GPS coordinates, and XMP XML text in your terminal, or extract raw binaries:

# In-place preview: prints metadata blocks summary, EXIF tags table, GPS table, and syntax-highlighted XMP XML
heic metadata dump photo.heic

# Machine-readable JSON tree with parsed EXIF tags and decoded UTF-8 XMP content
heic metadata dump photo.heic --json

# Extract raw EXIF or XMP binary to a separate file
heif metadata extract photo.heic --type exif --out photo_exif.bin -y

API Reference

class pylibheif.HeifContext

Manages the valid lifetime of libheif context. It is the main entry point (root object) for high-level API.

Methods

__init__() Creates a new empty context.

read_from_file(filename: str) -> None Reads a HEIF file from the given filename.

• filename: Path to the HEIF file.

read_from_memory(data: bytes) -> None Reads a HEIF file from a bytes-like object (bytes, bytearray, memoryview).

• data: Bytes-like buffer containing the file content.

read_from_stream(stream: Any) -> None Reads HEIF data directly from a Python file-like stream object implementing read(), seek(), tell().

• stream: A stream object such as io.BytesIO or open('...', 'rb').

write_to_file(filename: str) -> None Writes the current context to a file.

• filename: Destination path.

write_to_bytes(copy: bool = True) -> bytes | memoryview Writes the current context to binary output.

• copy: If True (default), returns a standard immutable Python bytes object (involves one memory copy). If False, returns a zero-copy read-only memoryview.

write_to_memoryview() -> memoryview Directly exports the encoded HEIF binary data as a zero-copy read-only Python memoryview.

• Fully lifecycle-safe (backed by an internal C++ capsule that persists even after context closure).
• Eliminates memory copies and avoids memory peak doubling.

write_to_stream(stream: Any) -> None Writes HEIF data directly to a Python file-like stream object implementing write().

• stream: A writable stream object such as io.BytesIO or open('...', 'wb').

get_primary_image_handle() -> HeifImageHandle Gets the handle for the primary image in the file.

• Returns: HeifImageHandle for the primary image.

get_image_handle(id: int) -> HeifImageHandle Gets the handle for a specific image ID.

• id: The ID of the image (see get_list_of_top_level_image_IDs).
• Returns: HeifImageHandle.

get_list_of_top_level_image_IDs() -> List[int] Gets a list of IDs of all top-level images in the file.

• Returns: List of integer IDs.

add_exif_metadata(handle: HeifImageHandle, data: bytes) -> None Adds EXIF metadata to the specified image.

• handle: Image handle from encoding.
• data: Raw EXIF bytes (with 4-byte offset prefix for TIFF header).

add_xmp_metadata(handle: HeifImageHandle, data: bytes) -> None Adds XMP metadata to the specified image.

• handle: Image handle from encoding.
• data: XMP XML as bytes.

add_generic_metadata(handle: HeifImageHandle, data: bytes, item_type: str, content_type: str = "") -> None Adds generic/custom metadata to the specified image.

• handle: Image handle from encoding.
• data: Raw metadata bytes.
• item_type: Metadata item type (e.g. "json", "iptc").
• content_type: Optional MIME content type (e.g. "application/json").

class pylibheif.HeifImageHandle

Represents a compressed image within the HEIF file.

Properties

• width (int): The width of the image.
• height (int): The height of the image.
• has_alpha (bool): True if the image has an alpha channel.
• has_content_light_level (bool): True if CLLI metadata is present.
• has_mastering_display_colour_volume (bool): True if MDCV metadata is present.
• has_ambient_viewing_environment (bool): True if AMVE metadata is present.
• content_light_level (Optional[HeifContentLightLevel]): CLLI metadata if present, otherwise None.
• mastering_display_colour_volume (Optional[HeifMasteringDisplayColourVolume]): MDCV metadata if present, otherwise None.
• ambient_viewing_environment (Optional[HeifAmbientViewingEnvironment]): AMVE metadata if present, otherwise None.

Methods

decode(colorspace: HeifColorspace = HeifColorspace.RGB, chroma: HeifChroma = HeifChroma.InterleavedRGB) -> HeifImage Decodes the image handle into an uncompressed HeifImage.

• colorspace: Target colorspace (default: RGB).
• chroma: Target chroma format (default: InterleavedRGB).
• Returns: Decoded HeifImage.

get_metadata_block_ids(type_filter: str = "") -> List[str] Gets a list of metadata block IDs attached to this image.

• type_filter: Optional filter string (e.g. "Exif", "XMP").
• Returns: List of metadata ID strings.

get_metadata_block_type(id: str) -> str Gets the type string of a specific metadata block.

• id: Metadata ID.
• Returns: Type string (e.g. "Exif").

get_metadata_block(id: str) -> bytes Gets the raw data of a metadata block.

• id: Metadata ID.
• Returns: bytes object containing the metadata.

class pylibheif.HeifImage

Represents an uncompressed image containing pixel data. Supports zero-copy memory access via nanobind's ndarray integration.

Properties

• width (int): The width of the image.
• height (int): The height of the image.
• has_content_light_level (bool): True if CLLI metadata is present.
• has_mastering_display_colour_volume (bool): True if MDCV metadata is present.
• has_ambient_viewing_environment (bool): True if AMVE metadata is present.
• content_light_level (Optional[HeifContentLightLevel]): Get or set CLLI metadata.
• mastering_display_colour_volume (Optional[HeifMasteringDisplayColourVolume]): Get or set MDCV metadata.
• ambient_viewing_environment (Optional[HeifAmbientViewingEnvironment]): Get or set AMVE metadata.

Methods

__init__(width: int, height: int, colorspace: HeifColorspace, chroma: HeifChroma) Creates a new empty image.

• width: Image width.
• height: Image height.
• colorspace: Image colorspace.
• chroma: Image chroma format.

add_plane(channel: HeifChannel, width: int, height: int, bit_depth: int) -> None Adds a new plane to the image.

• channel: The channel type (e.g. HeifChannel.Interleaved).
• width: Width of the plane.
• height: Height of the plane.
• bit_depth: Bit depth (e.g. 8).

get_plane(channel: HeifChannel, writeable: bool = False) -> np.ndarray Gets a zero-copy NumPy array mapping to the image plane memory.

• channel: The channel to retrieve.
• writeable: Whether the buffer should be writable.
• Returns: numpy.ndarray mapped to the underlying libheif memory.

class pylibheif.HeifEncoder

Controls the encoding process.

Properties

• parameters (HeifEncoderParametersProxy): A dictionary-like interface providing access to all configurable encoder parameters. It dynamically routes settings to the correct type-safe setters with validation.

Methods

__init__(format_or_descriptor: Union[HeifCompressionFormat, HeifEncoderDescriptor], preset: str = "") Creates a new encoder with an optional speed preset.

• format_or_descriptor: Compression format or specific encoder descriptor.
• preset: Initial preset ("ultrafast", "fast", "balanced", "quality"). If omitted, uses global default preset ("balanced").

apply_preset(preset: str) -> None Applies a cross-codec preset. Automatically maps to native parameters (x265: preset, aom: speed + threads + auto-tiles) and introspects parameter support to safely avoid unsupported parameter exceptions.

has_parameter(name: str) -> bool Checks whether the current encoder supports a given parameter name.

set_parameters(params: dict[str, str]) -> None Sets multiple encoder parameters in batch from a dictionary.

set_lossy_quality(quality: int) -> None Sets the quality for lossy compression (0-100).

set_lossless(lossless: bool) -> None Enables or disables lossless compression.

set_parameter(name: str, value: str) -> None Sets a low-level encoder parameter as a string.

get_parameter(name: str) -> str Gets the string representation of a parameter value.

set_integer_parameter(name: str, value: int) -> None get_integer_parameter(name: str) -> int set_boolean_parameter(name: str, value: bool) -> None get_boolean_parameter(name: str) -> bool set_string_parameter(name: str, value: str) -> None get_string_parameter(name: str) -> str Type-safe getters and setters for parameter values.

encode_image(context: HeifContext, image: HeifImage, preset: str = "") -> HeifImageHandle Encodes the given image and appends it to the context.

• context: Destination HeifContext.
• image: Source HeifImage to encode.
• preset: Optional encoder preset override ("ultrafast", "fast", "balanced", "quality"). Safe across all codecs (x265, aom, kvazaar).

Encoder Parameters Introspection

pylibheif supports inspecting and dynamically validating encoder parameters at runtime using encoder.parameters.

class pylibheif.HeifEncoderParameter

Describes a parameter supported by the selected encoder.

• name (str): Parameter name.
• type (HeifEncoderParameterType): Data type of the parameter (Integer, Boolean, or String).
• has_default (bool): Whether the parameter has a default value.
• default_value (Union[int, bool, str, None]): The default value.
• valid_integer_range (Optional[Tuple[int, int]]): Min and max allowed integers if bounded.
• valid_integer_values (Optional[List[int]]): Specific allowed integers.
• valid_string_values (Optional[List[str]]): Specific allowed string choices.

enum pylibheif.HeifEncoderParameterType

• Integer
• Boolean
• String

HDR Metadata Classes

class pylibheif.HeifContentLightLevel

Holds Content Light Level Information (CLLI) as integers.

• max_content_light_level (int): Maximum content light level (MaxCLL) in nits.
• max_pic_average_light_level (int): Maximum picture average light level (MaxFALL) in nits.

class pylibheif.HeifMasteringDisplayColourVolume

Holds Mastering Display Colour Volume (MDCV) metadata. All coordinates are normalized CIE 1931 xy floating-point coordinates.

• red_primary (Tuple[float, float]): Chromaticity coordinates (x, y) of the red primary.
• green_primary (Tuple[float, float]): Chromaticity coordinates (x, y) of the green primary.
• blue_primary (Tuple[float, float]): Chromaticity coordinates (x, y) of the blue primary.
• white_point (Tuple[float, float]): Chromaticity coordinates (x, y) of the white point.
• max_luminance (float): Maximum display mastering luminance in nits.
• min_luminance (float): Minimum display mastering luminance in nits.

class pylibheif.HeifAmbientViewingEnvironment

Holds Ambient Viewing Environment (AMVE) metadata.

• ambient_illumination (float): Ambient illumination in lux.
• ambient_light (Tuple[float, float]): Chromaticity coordinates (x, y) of the ambient light.

class pylibheif.AsyncHeifContext

Asynchronous wrapper for HeifContext. Operations are awaited and offloaded to a background thread pool executor without blocking the asyncio event loop.

Methods

async from_file(filename: str) -> AsyncHeifContext
async from_memory(data: bytes) -> AsyncHeifContext
async from_stream(stream: Any) -> AsyncHeifContext
Asynchronous factory methods to construct and read context.

async read_from_file(filename: str) -> None
async read_from_memory(data: bytes) -> None
async read_from_stream(stream: Any) -> None
async write_to_file(filename: str) -> None
async write_to_bytes(copy: bool = True) -> bytes | memoryview
async write_to_memoryview() -> memoryview
async write_to_stream(stream: Any) -> None
get_primary_image_handle() -> AsyncHeifImageHandle
get_image_handle(id: int) -> AsyncHeifImageHandle

Global Functions & Configuration

Codec Multithreading & Presets

• get_default_encoder_preset() -> str: Gets the global default encoder preset ("balanced" by default).
• set_default_encoder_preset(preset: str) -> None: Sets the global default encoder preset ("ultrafast", "fast", "balanced", "quality"). Can also be configured via PYLIBHEIF_ENCODER_PRESET environment variable.
• get_default_num_threads() -> int: Gets default codec threads for decode operations (auto-detected from CPU count and cgroup limits).
• set_default_num_threads(threads: int) -> None: Sets default codec threads (0 resets to adaptive auto-detection).
• get_default_codec_executor() / set_default_codec_executor() / shutdown_default_codec_executor(): Manages the dedicated background thread pool for async codec tasks.

Pillow Interoperability

• register_pillow_opener() / unregister_pillow_opener(): Registers or unregisters pylibheif as Pillow's HEIF/AVIF image opener and saver.
• to_pillow(source, convert_hdr_to_8bit=True) -> PIL.Image.Image: Converts HeifImage or HeifImageHandle into a Pillow Image.
• from_pillow(pil_image: PIL.Image.Image, bit_depth: int = 8) -> HeifImage: Converts a Pillow Image into a HeifImage.

class pylibheif.AsyncHeifImageHandle

Asynchronous wrapper for HeifImageHandle.

Methods

async decode(colorspace, chroma) -> HeifImage Asynchronously decodes the image.

class pylibheif.AsyncHeifEncoder

Asynchronous wrapper for HeifEncoder.

Properties

• parameters (HeifEncoderParametersProxy): Synchronous dictionary-like proxy to access and set encoder parameters.

Methods

async encode_image(ctx, image, preset="") -> HeifImageHandle Asynchronously encodes the image.

Enums

pylibheif.HeifColorspace

• RGB, YCbCr, Monochrome, Undefined

pylibheif.HeifChroma

• InterleavedRGB: Interleaved R, G, B bytes.
• InterleavedRGBA: Interleaved R, G, B, A bytes.
• C420: YUV 4:2:0 planar.
• C422: YUV 4:2:2 planar.
• C444: YUV 4:4:4 planar.
• Monochrome.

pylibheif.HeifChannel

• Interleaved: For interleaved RGB/RGBA.
• Y, Cb, Cr: For YUV planar.
• R, G, B: For RGB planar.
• Alpha: For Alpha channel.

pylibheif.HeifCompressionFormat

• HEVC: H.265 (libx265).
• AV1: AV1 (AOM/RAV1E/SVT).
• JPEG: JPEG.
• JPEG2000: JPEG 2000 (OpenJPEG).

Building from Source

# Clone with submodules
git clone --recursive https://github.com/your-username/pylibheif.git
cd pylibheif

# Build
uv pip install -e .

Performance

Benchmarks on 1920x1080 (HD) RGB real-world images (Apple Silicon), comparing python libraries and codecs.

Key Findings:

1. Ultra-Fast Stream I/O: The C++ buffered stream adapter with 64KB chunks and redundant seek elimination delivers microsecond-level overhead (3.18 μs write, 8.10 μs read) with zero-copy buffer integration, exceeding 314k OPS.
2. Decoding Parity & Parallelism: pylibheif delivers direct zero-copy decode speeds (~60.9 ms with 4 codec threads, ~62.0 ms default) fully matching specialized PIL extensions while providing direct access to native pointers and NumPy arrays without intermediate copies.
3. HEVC Encoding Performance: The bundled kvazaar encoder significantly outperforms x265 (~177 ms vs ~245-263 ms) with identical lossy quality and seamless API integration.
4. AV1 Speed Optimization: With automatic tile threading and speed preset mapping, pylibheif brings AV1 encoding down from ~292 ms to ~268 ms on 1080p frames.

-----------------------------------------------------------------------------------------------------------------------------------
Name                                                 Mean            OPS  Comment
-----------------------------------------------------------------------------------------------------------------------------------
test_benchmark_stream_write_performance           3.18 μs     314,076.00  (pylibheif 64KB buffered stream write)
test_benchmark_stream_read_performance            8.10 μs     123,444.82  (pylibheif zero-copy stream read)
test_benchmark_decode_hevc_parallel              60.90 ms          16.42  (pylibheif 4-thread decode)
test_benchmark_decode_hevc_pillow                61.41 ms          16.28  (pillow-heif)
test_benchmark_decode_hevc                       62.02 ms          16.12  (pylibheif direct decode)
test_benchmark_encode_kvazaar                   177.52 ms           5.63  (pylibheif, kvazaar, Q80)
test_benchmark_encode_hevc_pillow               245.65 ms           4.07  (pillow-heif, x265, Q80)
test_benchmark_encode_hevc                      263.61 ms           3.79  (pylibheif, x265, Q80)
test_benchmark_encode_av1                       268.61 ms           3.72  (pylibheif, aom, speed=6)
-----------------------------------------------------------------------------------------------------------------------------------

Run benchmarks yourself:

uv pip install pillow-heif pytest-benchmark
uv run pytest tests/test_benchmark.py tests/test_stream_benchmark.py --benchmark-only --benchmark-min-rounds=20

License

This project is licensed under the LGPL-3.0 License - see the LICENSE file for details.

Acknowledgments

• libheif - HEIF/AVIF codec library
• nanobind - Modern C++/Python bindings