Re: how to detect if a jpeg file is progressive or not
H.S.(email@example.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)
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.
In a few minutes a computer can make a mistake so great that it would
take many men many months to equal it.