

  IMPORTANT INFORMATION ABOUT ROTATING VERY LARGE JPEGS
  =====================================================

If you read the !Help file, you should know that !Jclean is
partially a front end for the Independent JPEG Group utility
'jpegtran' and there's not much I can do about the method
used by jpegtran, or how long it takes.

If jpegtran cannot get enough memory to perform transforms,
such as 90 degree rotations, in RAM workspace, it will use
the hard drive as workspace. This is considerably slower and
tests have shown that rotating a 2400 by 1800 JPEG takes
very nearly two hours. Rotating a JPEG of this size requires
in excess of 28 MB of work space. Until recently, such very
large JPEGs were rare. Now, digital camera technology has
made them quite common.

I intend writing code for !Jclean and !Jcut which will
intelligently test whether the RAM available is sufficient
for performing a required transformation in memory. If not,
it will split the JPEG into several sections, transform each
independently, and then recombine the sections into a
single, transformed JPEG. Version 4 of !Jclean is a rewrite
which, among other changes, puts the structures in place to
enable this process to be carried out effectively. It does
not yet do it.

Until then, I offer the following solution which will rotate
very large JPEGs by 90 degrees in no more than 2 or 3
minutes each.

Download my !Jcut and !Jigwas applications from.
  
  http://www.dacha.freeuk.com/free/


To rotate a very large JPEG - CLOCKWISE
=======================================

Run !Jcut and click Select on the icon to open the action
window. Set the zoom to 50% and dithering to none (for
quickest display) then drop your large JPEG onto the
leftmost-topmost icon in the action window or onto the !Jcut
icon bar icon. The displayed JPEG will probably cover the
action window so click Select on the icon bar icon again to
display the action window.

About 2/3 of the way down the left side of the action window
is a set of 7 buttons. The 3rd one shows 2 horizontal lines.
Click ADJUST over this button and 2 vertical lines will
appear on the image. Now look at the right side of the
action window. Select the radio button which says "3
sections", tick "Transformed" and select the 90 degree
clockwise option, change the directory name in the writable
icon to whatever you want and drag the directory icon to a
filer window. It will take maybe a minute to save out 3
rotated JPEGs.

Now run !Jigwas. Drop the directory onto the icon bar icon.
Make sure the "JPEG columns x rows" shows "1 x 3", then
click "Proceed". In about another minute, !Jigwas should
write a single joined JPEG with the same name as the
directory but with "/jpg" added to it. This should be a
correctly rotated version of the original.


To rotate a very large JPEG - ANTICLOCKWISE
===========================================

If you want to rotate a JPEG by 90 degrees anticlockwise,
you must perform the same actions as above but with these
differences:

In !Jcut -

  Use SELECT on the 3rd button showing 2 horizontal lines,

  Select the anticlockwise rotate option.

In !Jigwas -

  Ensure the array says "3 x 1".


Other transformations
=====================

Some of the other transformations may require less RAM
workspace and so this temporary measure of using !Jcut and
!Jigwas might not be necessary.

All of the transformations available in !Jclean can be
performed by splitting the JPEG into 3 sections,
transforming, and then recombining. You must determine
whether vertical or horizontal cuts are required.


Incomplete edge blocks on JPEGs
===============================

JPEGs from digital cameras will not have incomplete edge
blocks. JPEGs from other sources might have. See !Jclean's
!Help file for an explanation of incomplete edge blocks.

In most cases, any incomplete edge blocks will not transform
correctly and are best trimmed at the time of transformation.


=================END OF INFORMATION FILE================
