Why do jpegs get smaller?

in Mac Software edited January 2014
Why do jpegs saved using applescript take up less space than when they come off the camera?

I use a Nikon Coolpix990 and most of the images saved in high quality jpegs take up 1.1 Meg or so. If I do a rotate using the applescript toolbar script, it is saved a sa jpeg of 898 or so k. Sometimes less.

My concern is am I losing any valuable information or is this due to improved compression routines used by MacOSX such as Quicktime or Quark?

It is a concern to me, and may be important to others (Personally, I would like to build a proper save dialogue into the Applescript toolbar routines so I can choose the photo size and quality.)

added: this appears to happen with iPhoto as well. Does anyone know why?



  • Reply 1 of 1
    There is no such "improved" JPEG compression with OS X. Once you rotate your picture, it has to be recompressed in order for you to save it as a JPEG. Since JPEG is lossy, you are indeed losing some of your valuable information. If you don't want to lose any more data, save it as a png or tiff or pict.
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