https://github.com/hhrutter/lzw
An extended version of compress/lzw.
https://github.com/hhrutter/lzw
Last synced: 9 months ago
JSON representation
An extended version of compress/lzw.
- Host: GitHub
- URL: https://github.com/hhrutter/lzw
- Owner: hhrutter
- License: bsd-3-clause
- Created: 2019-08-26T23:32:40.000Z (almost 7 years ago)
- Default Branch: master
- Last Pushed: 2023-04-09T18:29:50.000Z (about 3 years ago)
- Last Synced: 2025-06-04T19:54:52.955Z (12 months ago)
- Language: Go
- Homepage:
- Size: 54.7 KB
- Stars: 8
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# Note
* This is a consolidated version of [compress/lzw](https://github.com/golang/go/tree/master/src/compress/lzw) that supports GIF, TIFF and PDF.
* Please refer to this [golang proposal](https://github.com/golang/go/issues/25409) for details.
* [github.com/hhrutter/tiff](https://github.com/hhrutter/tiff) uses this package to extend [x/image/tiff](https://github.com/golang/image/tree/master/tiff).
* [pdfcpu](https://github.com/pdfcpu/pdfcpu) uses this package for processing PDFs with embedded TIFF images.
## Background
* PDF's LZWDecode filter comes with the optional parameter `EarlyChange`.
* The type of this parameter is `int` and the defined values are 0 and 1.
* The default value is 1.
This parameter implies two variants of lzw. (See the [PDF spec](https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf)).
[compress/lzw](https://github.com/golang/go/tree/master/src/compress/lzw):
* the algorithm implied by EarlyChange value 1
* provides both Reader and Writer.
[x/image/tiff/lzw](https://github.com/golang/image/tree/master/tiff/lzw):
* the algorithm implied by EarlyChange value 0
* provides a Reader, lacks a Writer
In addition PDF expects a leading `clear_table` marker right at the beginning
which is not something [compress/lzw](https://github.com/golang/go/tree/master/src/compress/lzw) takes into account.
There are numerous PDF Writers out there and for arbitrary PDF files using the LZWDecode filter the following can be observed:
* Some PDF writers do not write the EOD (end of data) marker.
* Some PDF writers do not write the final bits after the EOD marker.
## Goal
An extended version of [compress/lzw](https://github.com/golang/go/tree/master/src/compress/lzw) with reliable support for GIF, TIFF and PDF.