HEIF/HEIC Image Format: Complete Technical Guide to Apple's High Efficiency Format

HEIF/HEIC: Apple's Modern Image Standard

High Efficiency Image Format (HEIF) is Apple's answer to JPEG—a container standard that leverages modern video codecs (primarily HEVC/H.265) to achieve 25–50% better compression than JPEG while supporting advanced features like transparency, HDR, depth maps, and multiple images per file. The .heic extension denotes HEIF containing HEVC; .heif is more generic, supporting HEVC or other codecs (AV1, VP9).

HEIF Container Architecture: ISO Base Media File Format

HEIF is built on ISO Base Media File Format (ISOBMFF)—the same box-based structure as MP4. Every HEIF file is composed of boxes (atoms), each with an 8 or 16-byte header:

[Box Size: 4 bytes] [Box Type: 4 bytes (e.g., 'ftyp', 'meta')] [Box Content]

Essential HEIF boxes:

• ftyp (File Type): Declares format brand (e.g., mif1 = HEIF with HEVC, heic = HEIC with HEVC), version, and compatibility
• meta (Metadata): Container for image metadata, EXIF, ICC profiles, color space (CICP), and primary image reference
• iloc (Item Location): Maps item IDs to data extents (byte ranges where image data lives)
• iinf (Item Info): Lists all items (images, thumbnails, depth maps) and their properties
• iprp (Item Properties): Stores shared properties (dimensions, colour space, transforms, rotation) referenced by items via property association boxes
• mdat (Media Data): Raw image/video data (HEVC bitstream, motion data, etc.)
• pitm (Primary Item): Indicates which item is the primary image (shown by default)
• infe (Item Info Entry): Describes individual items (name, type, hidden flag)

A simplified HEIF structure:

ftyp (brand: mif1 / heic)
meta
  hdlr (handler type: pict)
  iloc (item locations)
  iinf (item info)
  iprp (properties)
    ipco (property container)
      ispe (image spatial extents: width × height)
      colr (colour space)
      pixi (pixel information: depth per channel)
      irot (rotation: 0°, 90°, 180°, 270°)
      rloc (relative location)
      clap (clean aperture)
    ipma (item property association)
  pitm (primary item ID)
mdat (HEVC bitstream / raw pixel data)

HEVC Codec Integration: Video Codec as Image Engine

HEIF's compression strength derives from HEVC (H.265)—a modern video codec originally designed for 4K video. HEVC is packed into HEIF as a bitstream, decoded frame-by-frame to produce still images.

HEVC intra-frame encoding (key to still images):

• CTUs (Coding Tree Units): 64×64 pixel blocks (vs. JPEG's 8×8)
• Intra prediction modes: 35 angular + planar modes (vs. JPEG's simple DC/AC)
• CABAC entropy coding: Context-adaptive arithmetic coding; 30–40% better than JPEG's Huffman
• Transform coding: Varied block sizes (4×4, 8×8, 16×16, 32×32) matched to content
• Loop filtering: Deblocking + SAO (sample adaptive offset) for smoother output

Result: A 2 MP image (~6 MB as JPEG) compresses to ~2–3 MB as HEIC—matching or beating PNG's lossless size while retaining photographic quality.

Transparency and Additional Images: Aux Images and Depth Maps

HEIF supports auxiliary images (aux items) beyond the primary photo:

• Alpha plane: Separate HEVC-encoded transparency mask; stores per-item auxC box referencing the alpha
• Depth map: Disparity/depth information for focus stacking or 3D reconstruction
• Derived images: Thumbnails, alternative rotations—stored compactly as references to shared CTU data (avoiding duplication)

Example metadata:

<!-- Primary image (ID 1) with associated alpha (ID 2) and depth (ID 3) -->
<primary_item id="1"/>
<auxiliaryImage id="2" type="urn:mpeg:heaac:2015:aux:alpha" for_item_id="1"/>
<auxiliaryImage id="3" type="urn:mpeg:heaac:2015:aux:depth" for_item_id="1"/>

HDR and Colour Space: CICP and ICC

HEIF natively supports HDR (High Dynamic Range) imagery via:

• Colour profile (CICP): Specifies colour primaries (BT.709, DCI-P3, BT.2020), transfer function (SDR linear, PQ, HLG for HDR), and matrix coefficients
• Bit depth: 8-bit SDR, 10-bit HDR (Rec. 2020 / DCI-P3), or 12-bit cinema
• ICC profile: Full colour management (same as TIFF/JPEG)

A HEIC with colr box specifying BT.2020 + PQ transfer signals HDR10 content; display-side tone-mapping converts for SDR displays.

Encoding HEIF: FFmpeg and Apple Tools

FFmpeg with libx265:

# Lossy HEIC at quality 28 (0–51, lower = better; ~JPEG quality)
ffmpeg -i photo.jpg -c:v libx265 -crf 28 \
  -tag:v hvc1 -f heic photo.heic

# Lossless HEIC
ffmpeg -i photo.png -c:v libx265 -x265-params lossless=1 \
  -tag:v hvc1 photo_lossless.heic

# HDR10 (10-bit HEVC → BT.2020 PQ)
ffmpeg -i hdr_source.exr -c:v libx265 -x265-params crf=28:colorprim=bt2020:transfer=smpte2084 \
  photo_hdr.heic

Apple's macOS tools:

# Convert JPEG → HEIC (maintains quality)
sips -s format heic input.jpg --out output.heic

# Batch conversion (Photos app automation via AppleScript)
osascript -e 'tell application "Photos" to export selected to "/path/to/folder" as HEIC'

Python via Pillow (requires system libheif):

from PIL import Image
img = Image.open('photo.jpg')
img.save('output.heic', format='HEIF', quality=28)

Processing HEIF in Workflows

Web delivery:

<picture>
  <source srcset="photo.heic" type="image/heic">
  <source srcset="photo.webp" type="image/webp">
  <img src="photo.jpg" alt="Fallback">
</picture>

Batch conversion (Mac):

for file in *.heic; do
  ffmpeg -i "$file" -c:v libx265 -crf 26 "${file%.heic}.jpg"
done

Extracting metadata (Python):

from PIL import Image
from PIL.Image import Exif
img = Image.open('photo.heic')
exif = img.getexif()
print(exif.get(271))  # Camera make

Comparison: HEIF vs JPEG, PNG, AVIF, WEBP

When to Choose HEIF

• Apple ecosystem: iOS/macOS native; iPhone photos default to HEIC
• HDR imagery: Professional photography, cinema, gaming assets
• Transparency + compression: Combine alpha channel with HEVC efficiency
• File archival: Deep metadata, auxiliary images, and quality in compact form
• Avoid HEIF if: Web delivery (browser support), Android devices, legacy software (pre-2020)

HEIF represents the future of image storage—combining video codec advances with a flexible container—but adoption remains limited outside Apple's ecosystem.

Related conversions

Most teams that read this guide convert images in one of these directions:

• JPG to WEBP
• PNG to JPG
• HEIC to JPG
• PNG to WEBP
• TIFF to PNG
• RAW to JPG