ThunderScan compression
From Just Solve the File Format Problem
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* [http://apple2online.com/web_documents/thunderscan_users_guide.pdf ThunderScan User's Guide] | * [http://apple2online.com/web_documents/thunderscan_users_guide.pdf ThunderScan User's Guide] | ||
* [http://apple2online.com/web_documents/thunderscan_iigs_software_guide.pdf ThunderScan GS Software Guide] | * [http://apple2online.com/web_documents/thunderscan_iigs_software_guide.pdf ThunderScan GS Software Guide] | ||
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Revision as of 14:51, 20 April 2013
Contents |
Overview
ThunderScan compression, or ThunderScan RLE, is a compressed image format for 4-bit grayscale images. It can be used in TIFF files, and is identified by TIFF compression code 32809.
Format
The compression scheme is pixel-oriented, and uses run-length encoding and delta encoding.
Each coded byte represents one of four things, as indicated by the two highest bits:
00xxxxxx = A run of pixels whose colors are the same as that of the previous pixel 01xxxxxx = Three pixels whose colors are very similar to that of the previous pixel 10xxxxxx = Two pixels whose colors are very similar to that of the previous pixel 11xxxxxx = A single pixel of arbitrary color
Software
- libtiff (read-only)
Sample files
- pics-3.8.0.tar.gz → libtiffpic/text.tif
Editors notes
Libtiff calls this format "the 4-bit compression algorithm used by the ThunderScan program", but we have not been able to confirm its origin. Nearly all the information about it comes from libtiff.
ThunderScan is a scanner device for Apple II computers.
