[Pan-users] Re: Error saving large JPEG image

[walt]

On 08/09/2009 10:50 AM, Paul Crawford wrote:
> ...
> This is a 2667 x 4000 pixel image, 1.8MB in size that renders correctly
> in pan's viewer, but the image is then corrupted (used here in the
> technical, rather than moral, sense) in 3 banded regions if saved to
> disk...

I think I've figured out what the problem is. Now, what to do about it.

The example you cited is not yencoded, it's uuencoded.  After perusing
wikipedia's article on uuencoding I think I can explain this much:

Here are the last few encoded lines from part 1 of the 3-part post:

M2;>A=K&CJ^W2(%G1]S`?)@]&KDM8UJ?5K-%EA`*-]\=Z2]:ZU)XTV$1LQQ\V
M<'N:N6VFR1PO;D9=?F!![5JK)"W-_0;>"WTR%50;F`W9ZU?-M!!O<$':00N<
M8^E9&G,\B9VC*]CZC^M17KSD3329"1XR1P?H*CEN[EQ5RYJ%RP\QE8C`^7G.
END ----- CUT HERE --- CUT HERE --- femjoy_111637_061.jpg

Note that every line begins with 'M' except that last one. The first
character in a uuencoded line encodes the number of bytes from the
original binary file that are represented in that particular line.

That number is decoded by finding the ascii value of 'M' and subtracting
32, i.e. 77 - 32 = 45, the number of bytes from the original jpeg encoded
in a single line of the posted file.

There are 4 uuencoded characters for every 3 binary bytes, so the number
of ascii characters in the uuencoded line is (45*4)/3, or 60.  If you
count the number of chars in each encoded line you will get 60. Cool, eh?

Now, that last line begins with 'E', so uudeview figures that this line
of code should contain (69-32)*4/3 characters, which is 49.3.  It then
reads the next 49 chars from that line and proceeds to uudecode them,
even though it produces garbage.

Seems like it should be simple to add a test for the word 'END', and
maybe when I'm more awake I can manage it.