codecs

Packages

This repository is maintained as a monorepo. This means that this repository, instead of containing a single project, contains many projects. If you explore our project structure, you'll see the following:

```bash packages # charls-js # libjpeg-turbojs # openjpegjs #

... # misc. shared configuration lerna.json # MonoRepo (Lerna) settings package.json # Shared devDependencies and commands README.md # This file ```

Transfer Syntaxes

List of DICOM Transfer syntaxes: https://www.dicomlibrary.com/dicom/transfer-syntax/. More on each transfer syntax, how they differ, and in which situations they excel can be found here: https://www.medicalconnections.co.uk/kb/Transfer-Syntax

Transfer Syntax is the language used in DICOM to describe the DICOM file format and the network transfer methods. 3 main variables are contained in the Transfer Syntax:

• VR: Implicit/Explicit
• Endianism: Little-Endian/BigEndian
• Pixel Data Compression

| Transfer Syntax UID | Transfer Syntax Name | Codec | |-------------------------|---------------------------------------------------------------------|----------------| | Uncompressed | | | | 1.2.840.10008.1.2 | Implicit VR Little Endian: Default DICOM Transfer Syntax | Little Endian | | 1.2.840.10008.1.2.1 | Explicit VR Little Endian | Little Endian | | 1.2.840.10008.1.2.2 | Explicit VR Big Endian | Big Endian | | Lossless Compressed | | | | 1.2.840.10008.1.2.4.57 | JPEG Lossless, Nonhierarchical (Processes 14) | ? | | 1.2.840.10008.1.2.4.70 | JPEG Lossless, Nonhierarchical (Processes 14 [Selection 1]) | ? | | 1.2.840.10008.1.2.4.80 | JPEG-LS Lossless Image Compression | CharLS | | 1.2.840.10008.1.2.4.90 | JPEG 2000 Image Compression (Lossless Only) | OpenJPEG | | 1.2.840.10008.1.2.5 | RLE Lossless | RLE | | Lossy Compressed | | | | 1.2.840.10008.1.2.4.50 | JPEG Baseline lossy process 1 (8 bit)* | libJPEG-turbo | | 1.2.840.10008.1.2.4.51 | JPEG Baseline lossy process 2 & 4 (12 bit) | libJPEG-turbo | | 1.2.840.10008.1.2.4.81 | JPEG-LS Lossy (Near-Lossless) Image Compression | CharLS | | 1.2.840.10008.1.2.4.91 | JPEG 2000 Image Compression | OpenJPEG | | 1.2.840.10008.1.2.4.92 | JPEG 2000 Part 2 Multicomponent Image Compression (Lossless Only)** | OpenJPEG? | | 1.2.840.10008.1.2.4.93 | JPEG 2000 Part 2 Multicomponent Image Compression** | OpenJPEG? | | MPEG | | | | 1.2.840.10008.1.2.4.100 | MPEG-2 | Not supported | | 1.2.840.10008.1.2.4.101 | MPEG-2 | Not supported | | 1.2.840.10008.1.2.4.102 | MPEG-4 | Not supported | | 1.2.840.10008.1.2.4.103 | MPEG-4 | Not supported | | Special | | | | 1.2.840.10008.1.2.4.94 | JPIP | Not supported | | 1.2.840.10008.1.2.4.95 | JPIP-Deflate | Not supported | | 1.2.840.10008.1.2.1.99 | Deflated Explicit VR Little Endian *** | Little Endian |

• * - 1.2.840.10008.1.2.4.50: 8-bit RGB can leverage the browser's built in decoder.
• ** - 1.2.840.10008.1.2.4.[92|93]: Not supported in previous image loaders; OpenJPEG may work with these

• *** - Unlike all other DICOM transfer syntaxes, the deflate transfer syntaxes compress the whole of the DICOM data (tags, lengths, VR etc.) rather than just the pixel data - this is done using the standard deflate mechanism as used in gzip etc.) It is therefore most suitable for non-pixel objects such as structured reports, presentation states etc.

• 5: JS Decoder

• 57 & 70: JS Decoder

• 1.2 & 2.1 & 99: JS Decoder

• 2.2: JS Decoder

CI

We are leveraging lerna to version and publish packages. Lerna adds tooling on top of yarn workspaces to enable monorepo functionality. Our lerna configuration/usage is confined to:

• package.json
• lerna.json
• .circleci/config.yml

Pull requests attempt to build and test packages that have been modified (when compared against the main branch). "Semantic commit" messages, and the files included in the commit, help lerna determine how package versions should be updated and what to include in changelogs. Example commit messages include:

• fix(charls-decode): should not break when no config option is provided
• feat(encode): add encode API method
• feat(encode): friendlier API method BREAKING_CHANGE

You can read more about the specific lerna features we're using here:

• lerna run <cmd>: Used in package.json
• lerna version: Used in .circleci/config.yml
• lerna publish: Used in .circleci/config.yml
• "Lerna filter options": Used in package.json (--since main)

You can read more about semantic commit messages here:

• Semantic commits

Codec Package Anatomy

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