JPEG File Sizes

I have a 2048 x 1536 image from my Oly C740 whichproduces a jpg file

direct from the camera of 1966kb.

 

Using various programs "save as" function, and without any

manipulation, I find that saving as a jpg results in varying file

sizes, although all are saved as 100% quality, as listed below:-

 

Photoshop Elements2: 2777kb

Picture Window Pro: 1925kb

Corel Photopaint: 3641kb

PhotoImpact: 2362kb

 

Exif data is retained for the first two, but not for the latter two.

 

Anyone offer an explanation?

They're recalculating the compression?

I think of JPGs as mathematical formulas that approximate the shades and shapes. Different software, different formulas.

There are a number of different formats defined within the JPEG standard - i.e. standard jpeg, or progressive jpeg, as well as different algorithms for compressing depending on which type of jpeg is selected, or how much compresion is to be applied. There may be additional data stored also, as you have noted with the exif data.<p>Steve

<a href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00CHU0">http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00CHU0</a>

Differences in chroma subsampling can explain part of the discrepancy.

I wrote an article for questions like this: <a href="http://www.photo.net/learn/jpeg/">Jpeg Compression</a> (http://www.photo.net/learn/jpeg/).

Thank you Gordon for the link to your excellent article.

A very good informative read.