What is the Delta Preview in File/Save As?

When I save a file with "File/Save As" I can check "delta preview" in the dialog box and the preview picture turns to grey. The online manual explains that the grey area is is the difference between the original picture and the new one but I really don't understand how this has to be interpreted.

Could anyone give me some hints on this? Thanks a lot in advance.

Kjartan

Hi,

Each time you save a JPEG file, you will lose a bit of the original information depending on how low/high the quality setting is, as JPEG is not a 100% lossless compression. But don´t worry - most of the time the loss of information is not visible at all. The delta preview shows you the virtual difference between the "JPEG" picture before and after the "Save" process. As long as you can see a grey area, everything is fine, because the loss of information has no visual impact on the photo. As soon as you scale down the quality settings, you will see more. These are the areas which will degrade significantly due to the stronger compression.

Hope this helps

Hoang-Tran