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

["H.S." <hs.samix@gmail.com>]

Wayne Topa wrote:

> All of the inages on our web site are converted with the 'quality 25'
> option.  I find a lot of sites with images that are 100K or more just
> take too long to load.  There are still a lot of us that live in the
> sticks and don't have access to anything but slow POT lines.  


Hi Wayne,

I tried your way and converted all the image with quality 25. You are
right, I couldn't notice any perceptual difference at normal size. The
different is noticable only if you magnify the image.

I had a total of 14 images of size 2272x1704 (taken by a 4 megapixel
digital camera). I reduced them in size (682x511 pixels; or to 30%) and
their quality (to 25). The reduced size images were taking a total of
2.7 MB at default quality. But by using quality 25, the disk space usage
reduced to 0.608 MB! This is a great improvement. (I am still getting
progressive jpegs as the output.)

Here is the command I used to do the conversion (it is a one long line):
$> for f in *.jpg; do echo "$f"; bn=`basename "$f" .jpg`; convert
-resize 30% -quality 25 -interlace plane "$f" ${bn}-small.jpg; done


Thanks,
->HS