Re: [GM-help] file size in conversion jpeg to pdf

[Bob F. <bfr...@si...>]

On Tue, 6 Oct 2009, Marco Atzeri wrote:
>
> It is just my feeling but probably in this case the
> wished/expected behavior should be:
>
> gm convert -compress jpeg -define jpeg:preserve-settings test.jpg test.pdf
>
> otherwise we have a small jpeg creating a large pdf, that
> is at least puzzling.

I agree that if the original was JPEG and the nature of the image is 
still reasonably compatible that JPEG compression should be used with 
preserve settings.  However, the nature of the image may have changed 
dramatically so that JPEG compression is not really suitable any more.

As a naive user, I would hope that the output is as compact as 
possible while preserving maximum image quality.  Most PDF viewers 
will support all of the PDF formats that GM can output so it makes 
more sense for GM to automatically detect the most suitable 
compression by default, but allow the user to explicitly specify it if 
they like.

As of yesterday's development snapshot, the preserve-settings mode is 
used if the Image compression setting is JPEG, JPEG compression is 
specifically requested, and no JPEG compression settings have been 
altered.  I have not yet addressed the PDF compression choices issue.

> I think you should at least update the documentation
>
> -compress <type>
>      the type of image compression
>      Choices are: None, BZip, Fax, Group4, JPEG,
>      Lossless,  LZW,  RLE or Zip.
>
>      Specify  +compress  to store the binary image in
>      an uncompressed format.  The default is the
>      compression type  of  the  specified image file.
>
> as it is misleading, at least for me.

This update would be misleading since the compression type of the 
input file is often not known.  There is also the problem that if the 
compression type of the input file is used, then the output file may 
become trash.  I have no intention to destroy people's images if it 
can be avoided.

In my experience, the image type (-type) should take precedence over 
compression (-compress).

Bob
--
Bob Friesenhahn
bfr...@si..., http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/