cite="mid:CAFWGNQW9JjnLUpDZ+zS4sEj+kBW0=j7=JVSNHJNKvgU890fyhA-at-mail.gmail.com">

> style="font:400 13.33px/19.99px
Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;text-decoration:none;word-spacing:0px;display:inline;white-space:normal;font-size-adjust:none;font-stretch:100%;float:none;background-color:transparent">Relicensing
without explicit approval of all copyright holders is
not

possible
in general. It is possible only in a few exceptional
cases.

For
example:

*
From GPLv2 to GPLv3 and from LGPLv2.1 to LGPLv3 style="font:400 13.33px/19.99px
Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent">
*
From LGPLv2.1 to GPLv2 and from LGPLv3 to GPLv3 style="font:400 13.33px/19.99px
Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent">
*
From 2-clause BSD to 3-clause BSD style="font:400 13.33px/19.99px
Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent">
*
From EUPL to GPL/LGPL/MPL/EPL/CPL/CeCILL style="font:400 13.33px/19.99px
Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent">
style="font:400 13.33px/19.99px
Arial,Helvetica,sans-serif;text-align:left;color:rgb(34,34,34);text-transform:none;text-indent:0px;letter-spacing:normal;overflow:visible;text-decoration:none;word-spacing:0px;white-space:normal;font-size-adjust:none;font-stretch:100%;background-color:transparent">
And
not much else.



I understand this is a problem, LLVM is currently
going through this issue, but I think it's worth at
least considering it instead of just dismissing it as
infeasible off hand.



Does anyone have any clue how many contributors there
have been to libPNG?

Ok, I cloned the git repo and ran `git shortlog
--summary --numbered`

There are only 5 contributors throughout the history
of the libpng repo



Here they are:



Andreas Dilger

Glenn Randers-Pehrson

Guy Schalnat

John Bowler

Mans Rullgard



Andreas Dilger has contributed 2089 commits, followed
by John Bowler with 109, after that it's in the single
digits commit count wise.

Please be cautious using commits to decide who is an author. 
Lack of evidence for is not evidence against.  Does this repo
actually go back to the very beginnings of libpng?  Was there a
previous repo (cvs, svn, ...) where not all history was migrated
to git?  Is it possible there was a code review process where the
actual author was not the one to actually do the git commit?  (I
believe git can distinguish committer from author, although it
isn't often used.)  Are there messages in the mailing list
archives that indicate early authorship?  I don't know anything
about the history of libpng, but I point this out because I just
went through a similar process on a different project. 

Jack