/prog/ challenge - Compressing Visual Novels

What makes VN companies come up with proprietary image/video/audio formats that compress worse than standard ones? Here's an example:

Proprietary format, original: 871KB
Proprietary format, recompressed[1]: 822KB
PNG: 676KB
Optimised PNG: 674KB
JPG (high): 221KB
JPG (medium): 125KB
JPG (low, artifacts start becoming obvious): 86.7KB

So they could be several times smaller while looking almost the same, and that's not even getting into things like difference encoding since the bulk of them are almost the same images with slight differences.

Here's the challenge: find an existing VN, and write a little utility to compress it to 1/2th its original size or less while maintaining all the content. You have until the end of the year.

[1] I RE'd the format and wrote a compressor for it, which performed better than the original while decompressing to the exact same data.

>>61
you know how I know you never worked in security for a major corporation? because you wouldn't have written this shit. here's the truth:
1. proprietary software uses open source libraries a lot - sometimes directly, occasionally developing their own solutions based on FOSS stuff if the license is too restrictive
2. corporate code monkeys are fucking horrible at their jobs
3. most vulnerabilities (as in individual errors in code that allow exploitation, not whole new classes of vulnerabilities) are found by fuzzing because finding vulns statistically gets exponentially harder with program size because programs are trees (this goes for both manual and automated tests)
4. because in corporate world everything is tied to a budget, bugs may go unfixed if the cost (of fixing) vs benefit (of preventing exploitation) doesn't look good. but because not all hackers have the same skillset, what looks like a tricky to fix DoS for a pentester might be a code execution for a russian black hat