LERC (Limited Error Raster Compression) is an open-source raster and image format plus a C++ library for rapid encoding and decoding with a user-defined maximum compression error per pixel. It supports many pixel data types and can be used directly from Python, with decoders available for JavaScript and C#.
Project status
- Actively maintained: Recent updates in 2026 (latest upstream push 2026-07-30, including Lerc v4.2.0 on 2026-07-23 and JS updates through 2026-07-02) indicate the project is currently being maintained rather than dormant.
- Update cadence: In the last ~7 weeks there were multiple updates (v4.2.0, js_v4.1.2), suggesting a roughly monthly to bi-monthly cadence recently, though earlier JS-only activity shows longer gaps (for example, 2023 releases, and then March 2026 activity).
AI summary generated
Recent updates
v4.2.0
This release (Lerc 4.2.0) introduces stricter safety limits around how large the input data and the resulting compressed Lerc blobs are allowed to be. The implementation adds dimension and blob-size checks intended to prevent integer overflow and malformed-header issues during encode/decode.
BreakingSecurityFeaturesjs_v4.1.2
Release js_v4.1.2 does not provide any publisher release notes. The only observed code change is a modification to a single WebAssembly binary file, OtherLanguages/js/src/lerc-wasm.wasm, with no accompanying textual diff.
v4.1.1
Release LERC 4.1.1 (v4.1.1) claims to fix two security issues. The code diff shows broader decoder hardening (bounds checks), changes to how min/max statistics are computed, and additional JavaScript wrapper API changes that are not mentioned in the release notes.
SecurityFeaturesjs_v4.1.1
js_v4.1.1 was published on 2026-03-19, but the publisher did not include any release notes or change log details. As a result, there is no documented information about new features, fixes, breaking changes, security, or dependency updates for this version.
v4.1.0
Release v4.1.0 is described in the notes as finalizing the rename of the Lerc Python package to pylerc. The actual diff shows additional cross-language changes, especially in the JavaScript/TypeScript WASM loader, exported typings, and decoding result shapes.
js_v4.0.4
Release js_v4.0.4 was published, but the publisher did not provide release notes. No explicit new features, breaking changes, bug fixes, security updates, or dependency changes are documented in the provided release information.
js_v4.0.3
Release js_v4.0.3 was published, but no release notes were provided by the publisher. As a result, there is no documented information about new features, bug fixes, breaking changes, or security updates in this release.
js_v4.0.2
Release js_v4.0.2 was published on 2023-10-27, but no release notes were provided by the publisher. As a result, there is no documented information about new features, fixes, security updates, or breaking changes to assess developer impact.
js_v4.0.1
Release js_v4.0.1 was published on 2022-07-19, but no release notes or change log details were provided by the publisher. As a result, there is insufficient information to identify new features, breaking changes, bug fixes, security updates, or migration steps.
v4.0.0
LERC 4.0.0 aligns the project with ArcGIS Pro 3.0 and introduces the wasm-based JavaScript decoder plus new 4D-oriented API functionality (for mixed valid/invalid values via per-band noData). The code diff also shows significant cross-language and build-system updates, including changes to JS loading/packaging and CMake packaging behavior.
BreakingFeaturesv3.0
This v3.0 release reorganizes the Lerc API to support per-band valid/invalid masks via a new nMasks parameter, and updates the underlying encode/decode implementations accordingly. Release notes from the publisher are not provided, so developers must rely on the code diff to understand the actual API and behavior changes.
Featuresv2.2.1
The v2.2.1 release notes claim a minor update focused on simplifying how LERC is built and installed as a Conda package for Python. The code changes confirm build packaging changes, but they also include several undocumented adjustments that can impact Conda install behavior, especially on Windows.
Featuresv2.2
This release is labeled as a general bug fix release (v2.2), but the provided release notes do not list any specific changes. The actual diff shows targeted decoder behavior changes in Lerc1 legacy header handling and Lerc2 decoding logic, plus substantial Python packaging and shared-library naming/loading changes.
Breakingv2.1
This release updates the LERC C++ codec to a newer internal “Lerc2 v5” implementation intended to interoperate with ArcGIS Pro 2.5 and ArcMap 10.8, while claiming backward readability of older LERC blobs. The actual code diff shows multiple substantive codec algorithm changes beyond what the short release notes describe, including new encoding modes for multi-band (nDim > 1) data and improved float handling. The default encoder output is now a newer bitstream version, which can break older decoders unless compatibility mode is explicitly used.
BreakingFeaturesv2.0
The release notes for v2.0 state that the LERC API and all language decoders were updated to be in sync with ESRI ArcMap 10.7 and ArcGIS Pro 2.3, and that LERC-encoded blobs from previous ArcMap/ArcGIS Pro versions can be decoded. No other behavioral, API, or bitstream changes are described.
v1.0.1
Release v1.0.1 is described as a patch that resolves a Huffman code table parsing issue (#31) in the decoders. The code diff confirms a JavaScript-side decoding change related to Huffman unstuffing, but it also contains several C++ API refactors not mentioned in the release notes.