Release 2.0.0

vendor/github.com/hhrutter/lzw/README.md

@@ -0,0 +1,37 @@
+# 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.