Re: [GM-help] Order of operations, and -size question

[john a. <jal...@ya...>]

Hrm. Ok.  So since in this case, I've got two conversions.  They are operating on the exact same original, with all of the same options, and are ultimately doing a -resize.
If I stick an additional '-size' option at the beginning, the file comes out:

- the same, visually (as best as my eyes are, anyway), 
- same resolution
- slightly bigger filesize (about 9% bigger) 
- >2x faster to process (!)

Check it out:

$ time /opt/local/bin/gm convert -limit Memory 512M  -limit Map 2048M  -limit Disk 2048M  -flatten ./3171145347_d490413003_o.jpg  -sharpen 1.00x0.95  -resize 1024x1365!    -interlace None -type TrueColor -quality 96 -sampling-factor 1x1 ./3171145347_d490413003_l.jpg ; ls -l ./3171145347_d490413003_l.jpg
/opt/local/bin/gm convert: Image sequence is required (unable to flatten image).

real    0m3.013s
user    0m2.817s
sys     0m0.130s

-rw-r--r--  1 user  user  1121101 May 22 17:31 ./3171145347_d490413003_l.jpg

$ time /opt/local/bin/gm convert -size 1024x1365 -limit Memory 512M  -limit Map 2048M  -limit Disk 2048M  -flatten ./3171145347_d490413003_o.jpg  -sharpen 1.00x0.95  -resize 1024x1365!    -interlace None -type TrueColor -quality 96 -sampling-factor 1x1 ./3171145347_d490413003_l2.jpg ; ls -l ./3171145347_d490413003_l2.jpg
/opt/local/bin/gm convert: Image sequence is required (unable to flatten image).

real    0m1.266s
user    0m1.147s
sys     0m0.066s
-rw-r--r--  1 user  user  1199339 May 22 17:31 ./3171145347_d490413003_l2.jpg

GM 1.3.5, compiled with the libjpeg with SIMD extensions (the japanese one).

What does it mean to have -size and -resize on the same line. I'm puzzled. Not complaining about it, but puzzled. If I can take the hit on the filesize, wondering if we shouldn't do this for the performance bump. :)
-j




----- Original Message ----
> From: Bob Friesenhahn <bfr...@si...>
> To: john allspaw <jal...@ya...>
> Cc: Requests for help with GraphicsMagick <gra...@li...>
> Sent: Wednesday, May 20, 2009 3:42:35 PM
> Subject: Re: [GM-help] Order of operations, and -size question
> 
> On Wed, 20 May 2009, john allspaw wrote:
> >
> > 1 - what does adding the "-size" parameter do to the conversion line?
> 
> Provided that -size is specified before the name of a JPEG file to 
> read, it instructs libjpeg to return a subresolution at least as large 
> as the specified size, but as small as possible.  This is done at the 
> JPEG DCT level so it is extremely efficient.  When the objective is to 
> produce much smaller versions of the JPEG image (e.g. thumbnails) this 
> is the best way to improve performance.
> 
> > 2 - as far as the various options are concerned, does it matter 
> > which order they're in? (sharpen,sampling-factor,interlace, etc.)
> 
> Yes, it does matter.  Options like sampling-factor and interlace are 
> used when saving a file, so they need to be specified prior to the 
> file to save.  Commands like -sharpen modify the image so they 
> should come after the filename to read and before the filename to 
> write.
> 
> I know that it is confusing.  Even more confusing is that in order to 
> support Unix conventions, GM also supports specifying options first. 
> I recommend always specifying options/commands in left to right order 
> and not relying on the automatic reordering feature.
> 
> Bob
> --
> Bob Friesenhahn
> bfr...@si..., http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
> 
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