Re: merged multiple jpeg files into multipage tiff: size grows, why?

Anthony Thyssen дµÀ:
> Zhang Weiwu on  wrote...
> | Dear list:
> | 
> | This is my first time try convert(1). I did this:
> | $ convert 1329.jpg 1330.jpg -adjoin identity.tiff
> | 
> | The two images are here:
> | gopher://sdf.lonestar.org/I/users/weiwu/1329.jpg
> | gopher://sdf.lonestar.org/I/users/weiwu/1330.jpg
> | 
> | Both images are less then 300KB in size, however the
converted tiff
> | image is as big as 1331KB. This is strange as tiff
file is twice as big
> | as it should be. As compression method shouldn't been
changed (still
> | JPEG inside the TIFF) I wonder how this comes to be
and, is there a way
> | to generate tiff image less then 600KB? Thanks in
advance!
> | 
> | I also tested the generated tiff image to make sure
it's still in JPEG
> | compression:
> | 
> Did you try adjusting the -quality setting for the
JPEG's?
>
> Does that make a difference?
>
> Also reading and re-saving JPEG files (with JPEG lossy
compression)
> is NOT a good idea.  Doing so degrades the image.  That
is the price you
> pay for using a higly compressed JPEG image.
>
> I do know know of a lossless insert of JPEG to TIFF
images.
> If there was it would proably make a good IM delegate
(external
> converter program).
>   
Well, my understanding is, that since re-saving is a lossy
operation,
convert(1) should try to avoid such operation, then the
default value
should be when doing converting, do not try to re-compress,
e.g. only
encapsulate the jpeg with TIFF format but not to touch the
raw image
data. I am not sure if this is possible but if it's
possible, there
should be an option letting convert(1) acting this way or
this should be
default behavior of convert(1). How do you think?
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Zhang Weiwu on  wrote...
| Anthony Thyssen дµÀ:
| > Zhang Weiwu on  wrote...
| > | Dear list:
| > | 
| > | This is my first time try convert(1). I did this:
| > | $ convert 1329.jpg 1330.jpg -adjoin identity.tiff
| > | 
| > | The two images are here:
| > | gopher://sdf.lonestar.org/I/users/weiwu/1329.jpg
| > | gopher://sdf.lonestar.org/I/users/weiwu/1330.jpg
| > | 
| > | Both images are less then 300KB in size, however
the converted tiff
| > | image is as big as 1331KB. This is strange as tiff
file is twice as big
| > | as it should be. As compression method shouldn't
been changed (still
| > | JPEG inside the TIFF) I wonder how this comes to be
and, is there a way
| > | to generate tiff image less then 600KB? Thanks in
advance!
| > | 
| > | I also tested the generated tiff image to make sure
it's still in JPEG
| > | compression:
| > | 
| Well, my understanding is, that since re-saving is a lossy
operation,
| convert(1) should try to avoid such operation, then the
default value
| should be when doing converting, do not try to
re-compress, e.g. only
| encapsulate the jpeg with TIFF format but not to touch the
raw image
| data. I am not sure if this is possible but if it's
possible, there
| should be an option letting convert(1) acting this way or
this should be
| default behavior of convert(1). How do you think?

This is what the 'delegate' conversion system is about. But
it does this
by avoiding reading in images.

However IM is by its nature a Image Manipulation Package. 
That means
for most situations it just decodes from a large number of
formats,
modifies the image, then writes it to one of a large number
of formats.

It would be imposible for it to know how to convert from one
format
directly to another, for ALL those formats.   With more than
100 formats
known, that means 10,000 different methods must be needed.

It is thus NOT POSIBLE for a general image converter to
handle what you
ask without decoding the lossy JPEG format.

Someone would have needed to write something specific for
TIFF to do
this.

I suggest you just don't save as JPEG compression in the
TIFF format,
or try to find a program that can do it without loss.  It is
not likely.


If you do find such a program. Great, let me know too, so I
can add a
note about it in IM Examples, for the TIFF format...
     http:/
/www.imagemagick.org/Usage/formats/#tiff



  Anthony Thyssen ( System Programmer )    <A.Thyssengriffith.edu.au>
 -----------------------------------------------------------
------------------
    It's only when you closely examine ants with a
magnifying glass
    do you realise how often they burst into flames.
 -----------------------------------------------------------
------------------
     Anthony's Home is his Castle     http://www.cit.gu.
edu.au/~anthony/
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