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 Readme for:  Graphics » Icon » iff_icon_data_decoder.zip

IFFIconDataDecoder

Description: Iff Icon Data Decoder snippets and PDF
Download: iff_icon_data_decoder.zip       (TIPS: Use the right click menu if your browser takes you back here all the time)
Size: 175kb
Version: 1.00
Date: 30 Nov 23
Author: Mike R.
Submitter: Mike R.
Email: riddle1264/yahoo com
Requirements: AROS with RTG screen
Category: graphics/icon
License: APL
Distribute: yes
FileID: 2768
 
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This documentation in PDF format and the
accompanying source code snippets are intended to help explain the
encoded storage format for the image data in the IMAG chunks for Glow Icons.
 
Main features include:
- DecodeRLE sample code for decoding run-length encoded data (8 bits). This is a
functional sample from my test program.
- DecodeBytes sample with bit shifting and masking to decode the IMAG image
bitstream data. This is also a functional sample.
- PDF document "IFF Icon Data Decoded.pdf" to help explain the complex encoding
scheme.
 ......

The image data for the IMAG chunks are encoded using a modified version of RLE
aka Run Length Encoding. It is a bitstream rather 
than a byte stream composed of RLE bytes and image data bytes.

Perhaps, the IFF icon image data storage format is a trade-off between
complexity and practicality. Because applying the RLE encoding 
to chunky data is much more efficient than applying the same encoding to planar
data the storage size is much smaller and thus much 
more practical for Amiga computers which in the early days had very limited
storage space. However, the storage format is complex and 
difficult to implement so bit shifting and masking is needed for encoding &
decoding.

 ......
 
Files included:
decodebytes_sample.c
IFF Icon Data Decoded.pdf

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