Re: how to detect if a jpeg file is progressive or not

[Wayne Topa <linuxone@intergate.com>]

H.S.(hs.samix@gmail.com) is reported to have said:
> Olafur Jens Sigurdsson wrote:
> 
> > Imagemagick does the trick for you.
> > 
> > To see if your files are interlaced or not you can use identify
> > -verbose filename.jpg and search for the Interlace line and if it says
> > None then it isnt a progressive jpeg and if it says Plane it is.
> 
> That was really great help. Thank a ton. The problem of identifying an
> image as progressive or not is solved.
> 
> > 
> > To convert from basic to progressive use convert infile.jpg -interlace
> > Plane outfile.jpg
> 
> The problem left is to convert all my current jpegs into progressive
> ones. jpegtran did the job (the following is one long command):
> $> for f in *.jpg; do echo "$f"; mv "$f" tmp.jpg; jpegtran  -progressive
> tmp.jpg  > "$f"; rm -f tmp.jpg; done
> 
> (I am sure there is a way to use the stdout and stdin in this procedure
> instead of tmp.jpg, but I didn't check)
H.S.

Having never heard of "a progressive jpeg" I was interested in your
query, and the answer you received.  

I tried out the conversion to "progressive" on some of my large jpegs
to see if it would help (as I have the same problem you have, dialup).

I used the suggested convert command on a 77K jpeg and it was
converted to 68K.  Not bad but I have been using a different convert
option and getting much better results.

convert -quality 25 infile.jpg outfile

That option got the 77K file down to 24K which is more manageable, for
me anyway.  I see no difference in the pictures but the size.

I would be interested in hearing your results with this option.

Wayne

-- 
In a few minutes a computer can make a mistake so great that it would
take many men many months to equal it.
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