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

Wayne Topa wrote:

>>This is a case of compression with a loss in quality. Note that you can
>>still have the new smaller image either as progressive or non-progressive.
> I don't see that loss in quality tho.  At 1280x1024 they look the
> same, to these old eyes anyway, and the savings in size sure is a help
> when you are sending images over a 26K POT line.

I see that I didn't elaborate properly. There is a lot of quality,
however the perceptual quality is not degraded that much. So to a
viewer, the smaller sized image file doesn't look that different from
the larger file image.

Basically, it boils down to decreasing the quality of the jpeg file
while maintaining the perceptual quality reasonably well.

>>I am still playing around to decide what size (in pixels) images to
>>upload for others to view and how much quality to encode the jpegs with.
>>In any case, I am planning to upload the larger size images only
>>progressive jpegs no matter what quality I use them.
> 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.  

I understand. I have a few friends who connect  through dialup and they
sometimes cannot get connections faster than about 42 kbps. If I am in a
situation where I see a larger file image is to be made available, I
usually show it's thumbnail and give links to larger image files, e.g.
"Medium (50KB)" and "Full (120KB)", so that the user can decide which
one he wants to download and view.

Having read your above comments, I am going to try this with my images
as well.

Thanks for your input,

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