I hope nobody takes this as legal advice; I'm not a lawyer but I'm fairly certain it's wrong. The font would still be the same work.
It comes down to this: Typefaces/glyphs are not copyrightable. The font code that produces those glyphs is.
> Typefaces cannot be protected by copyright in the United States (Code of Federal Regulations, Ch 37, Sec. 202.1(e); Eltra Corp. vs. Ringer)...However, there is a distinction between a font and a typeface. The machine code used to display a stylized typeface (called a font) is protectable as copyright. [1]
In software, a similar "black-box" derivation process has happened many times, e.g. UNIX/GNU. Copyrights applies to software source code, but not software functionality.
Determining what is the "essential, creative work" in each case in a nuanced way is a matter for courts and armies of lawyers: Apple round corners, Oracle Java APIs, etc.
[1] https://en.wikipedia.org/wiki/Intellectual_property_protecti...
(But yes, I do agree that typefaces are exceptionally commonly distributed.)
However the example here, and the situation with fonts seem different. It is the case that font data is viewed as utilitarian and uncopyrightable. So we have a copyrightable program, producing uncopyrightable data. The argument here seems that we have a copyrightable program producing copyrightable data.
> So the question reduces to how much the type of compression matters here
If you compress, you can copyright the compressed bytes.
If you don't compress, you can copyright the uncompressed bytes.
As far as that copyright extending to derivations, e.g. decompressions, the answer indeed situation-dependent. For example, converting a copyrighted font from TTF to WOFF does not remove the copyright. But converting a copyrighted font from TTF to screen pixels to WOFF removes the copyright. (Sorry I don't have a reference; probably findable.)
The "self-extracting zip" derivation would probably fall into the latter category; that is, the copyright would not transfer.
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But even if the copyright were maintained during your advanced decompression, one could argue that editing down to very specific portion of that extremely large body of work was a substantive/transformational derivation, which they could then copyright themselves.
Transformative works are very common in art. The most famous example is Duchamp simply adding a mustache to a print of da Vinci's Mona Lisa, and copyrighting that. [1]
[1] https://en.wikipedia.org/wiki/L.H.O.O.Q.