Adding caption to a jpeg file

[muranod]

I somehow had the assumption that adding caption info into a jpeg file in Imatch and then writing that into the file did not recompress the image, but I cannot verify that in the help or in the forum. Is the image quality affected by adding IPTC info, copyright, headline, etc. and then writing that into the metadata?

[JohnZeman]

While they're within the same file, I believe the JPG image is stored separately from the metadata.
So you're right, the image is not recompressed when you edit and save metadata, (I do that all the time with my JPGs and the image quality never changes).

[sinus]

Yep, John is correct.
For non-IT people to consider: imagine a car.

If you change metadatas like caption, headline and so on, you change a wheel. If it changes again, take the wheel away and put in a new one. Then again and so on.
The engine of the car is not touched at all. That means you can change the metadatas as often as you want, you just change one wheel accordingly.

Only when you change the image in Photoshop or another editor, then you tinkle with the engine. Otherwise he remains totally untouched.

I hope that picture's right, I think so.


And this is for IT-people: 
http://dev.exiv2.org/projects/exiv2/wiki/The_Metadata_in_JPEG_files

[Mario]

Adding or changing metadata will not change the image data (and thus not cause a re-compession of JPEG or other lossy image formats).

[muranod]

Thank you all. I thought that was the case, but wanted to reconfirm as I'm moving along through my camera jpegs.