ASCII Art Compression for IQ6900

Compression is typically divided into two types:

• Type where deduplication works
• Type where deduplication is ineffective

Version without Deduplication

This method guarantees a 59.83% compression rate for all images.

1. Map ASCII art to numbers from 0 to 6.
2. Convert from base 7 to base 10.
3. Convert from base 10 to base 127.

Decoding Method

• Convert from base 127 to base 10.
• Convert from base 10 to base 7.
• Map number to ASCII art.

Version with Deduplication

Since we aim to always use the more efficient compression, using this method means the compression rate would be 59.83% + α.

Custom RLE Compression Algorithm

We've modified RLE compression to create our custom compression algorithm.

1. Perform RLE-based compression.

   • Example: Characters with their repetition counts, like a1b2c3.

2. Separate characters and numbers, and map the characters to 0-6.

   • Example: a1b2c3 -> Number array [1, 2, 3] and character array [0, 1, 2] (where 'a' maps to 0, 'b' to 1, 'c' to 2).

3. Append the character array to the number array.

Note

• Formats like a12b2 would be useless because numbers should not exceed one digit. Thus, numbers are limited to 9.

4. Convert the decimal number array to base 127.

Decoding Method

• Convert from base 127 to base 10.
• Split the array into halves, then map the characters back using ASCII mapping.
• Perform RLE decoding.

Conclusion

With this method, we support over 59.83% lossless compression for ASCII art.