Digikam - does saving metadata to images degrade quality

[Guest]

I can't find a definitive answer to this anywhere.

Right now I save image metadata in Digikam only to Digikam's database. It would be convenient, however, to have the metadata stored in the images themselves (that way, when I share the pictues with family, they have my captions etc.). I know how to do this, BUT don't want to do if writing the metadata to the images (once or many times) would cause the images to degrade. In other words, does the jpeg image data get decompressed/recompressed when writing the metadata, or is it in a separate portion of the file that doesn't touch the image data?

When trying to research this, it seems that many think it depends on what software your using. Has anybody determined this (from experimentation or otherwise) for Digikam?

Thanks!!

[cowb0y]

Re: Digikam - does saving metadata to images degrade quality

Not sure about the technical details regarding how EXIF data (metadata) is stored in JPEGs, but it seems counterintuitive that it would require de/compression of the image data to update/add it. Of course, it's up to the individual application to behave in a reasonable manner. There are plenty of applications whose sole purpose is to manipulate EXIF data, so I doubt that they are even able to handle image compression. You may want to ask on one of the Digikam mailing lists for a more specific answer regarding digikam itself: http://www.digikam.org/drupal/contac...t#mailinglists.

[Teunis]

Re: Digikam - does saving metadata to images degrade quality

What's stopping you from trying :P

[dibl]

Re: Digikam - does saving metadata to images degrade quality

EXIF data is not part of the image. As it says here:

http://en.wikipedia.org/wiki/Exchang...ge_file_format

it is save in added metadata tags, that are provided for in the listed file formats, including JPEG. The tags are not the image -- they don't get compressed/decompressed. You can send your JPEG images to your family, and the EXIF data will be readable by any software that can see the tags (i.e. Gwenview, PaintShop Pro, etc. etc.).

If you were to extract/copy the EXIF data from the tags, and paste it into the image itself, then yes, it will be subject to the same compression/decompression effects as the rest of the image (unless you use TIFF format with no compression, of course). If you leave the EXIF data in the tags, then it will never change, regardless of enlarging or reducing the image.

[Teunis]

Re: Digikam - does saving metadata to images degrade quality

About trying, I took a photo and it's size is 4.689.981 bytes.

I displayed it in Gwenview and used the provided plug in to add a name of 16 characters and hit Apply.
The resulting photo's size is now 4.690.972 bytes.

Doesn't look like much of a loss.

As far as I know Gwenview and Digikam use the same KIPI plug ins.

[cowb0y]

Re: Digikam - does saving metadata to images degrade quality

I think what the OP is concerned about is that the application will decompress the image into a buffer to display it, etc., then recompress the image after the tags have been changed (i.e., "repackage" the file). Even at the same quality factor, this would be undesirable behavior (and poor application design).

[Teunis]

Re: Digikam - does saving metadata to images degrade quality

I agree with cowb0y, but it's highly unlikely the resulting size of the pic would be as close as in my example.
Further I was presented with an 'Apply' button, it didn't say 'Save'.

I know, all circumstantial but none the less...