[Digikam-users] jpeg compression

[Bjørn Kvisli]

Lørdag 30 juni 2007 18:34, skrev Arnd Baecker:
> Would it make sense to put a brief summary of the contents of this
> thread into a FAQ entry (eg. "Which image format should I choose?")?
>
> If yes, Bjorn, could you maybe set up a short text, which
> I could then put into the FAQ on the digikam homepage?
>
Arnd,
the attached file contains a short text on which file format to use. I am 
fairly new to this, so please change it as you see necessary if you decide to 
use it for the FAQ.

I did not write anything about the RAW format. The reason is that I could not 
find a good way to use it with Digikam. I could import the RAW files (nef 
files) from my Nikon D40 and edit them, but not save them. When trying to 
convert them to jpeg, I only got a file of about 961 kb without exif data. It 
seems like conversion from RAW to tiff worked, but most of the exif data were 
lost.

Has anyone else experience with the RAW files from Nikon D40?
Reagrds, Bjørn
> Alternatively, is there anything which should be added to
> handbook, which already has a detailed account on image formats, see
> http://docs.kde.org/development/en/extragear-graphics/digikam/using-filefor
>matsupport.html ?
>
> Best, Arnd
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WHICH FILE FORMAT TO USE

Most digital cameras store images in jpeg format on the memory card. Jpeg is a compressed format, which compression causes loss of quality. Heavy compression may make the loss of quality visible to the eye. Every time you open a jpeg image, edits it, saves the file and closes it, the image is compressed and quality lost. Lost quality can not be regained.

To avoid this repeated loss of quality you should edit your files in a lossless format. Digikam understands two of these: Tiff and png. In Digikam it is advisable to use png. Digikam supports the exif data in png files, whereas in tiff files, exif data are lost.

Using one of Digikam's batch process, you can easily convert all the jpeg files downloaded from your camera to png-files.

You have now finished editing your photos and are content with the results. Should you keep the png-files or convert them to the far smaller jpeg files for storage?. If you are very conserned with storage space, you can do the latter. You could, however rather keep the lossless png files and only create jpeg copies  in the moment you want to take your images to the print shop, send them by email or post them on the web.