The PIC2 image format

The PIC2 image format is used some Japanese personal computer users.
The PIC2 format is designed by A.Yanagisawa. It is very excellent format except for it's encode/decode speed ;-)

Features

• Powerful header informations (author, filename, title, saver, product number, created date and comment).
• Reversible compression, and very high compression ratio (In a lot of case, keep higher compression ratio than the JPEG compression. Especially, because of it's compression method, PIC2 is good at pictures like cell animation).
• Can handle full coloer(24 bits) image.
• Can include multi image blocks into one PIC2 file.
• Have four different block format (P2SS, P2SF, P2BM and P2BI). P2SS format uses arithmetric compression for storeing data. P2SF uses normal run length compression. P2BM and P2BI is raw image format. Select any one accoding to the situation.

The outline of the Compression algorithm of PIC2 format

1. In the first place, try to record pixel color, uses color caches which keep some recent colors, and formed accding to color's frequency. PIC2 has some color cache spaces that are switched by upper pixel value of current pixel. If cache is hit, record that.
2. Unfortunately, in the case of color cache didn't hit, record the difference from the value estimated with the value of upper and left pixel of current pixel
3. And extract image's color chain if exist, and record that (It results in image's outline).
4. In all time of recording values, it is pressed with arithmetric compression method which produce the ideal compression ratio in theory(P2SS).

The PIC2 module for XV

Supported internal formats

• Support 3,6,9,12,15,18,21,24bit PIC2 format(Load/Save).
• Support all image block formats of PIC2(Load/Save).
• Support multi block PIC2 file(Load/Save).

Bugs

• Unsupport 8bit PIC2 image file.

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