I feel I did not explain my idea in a way that the benefit is understood. Maybe it is because I am not a native English speaker, who knows. What I talk about is a (more or less) new image file format that adds something to existing image file formats that is similar to the pdf page boxes concept. I will give you an example use case:
Consider the scribus layout below.
You can see that the duck’s bill reaches into the page’s bleed. The original image may have allowed to add a little on the left so that one could now change the crop in a way that the end result (trimmed page) comes closer to the photographer’s intention. But now we have to cut the photograph in an unpleasant way.
Even if I do myself the photography and the page layout, I want to decide about the crop as early as possible. Usually, that leaves no space for minor corrections. With crop metadata understood by many programs would allow an extremely efficient workflow. Adding such an image in scribus may present something that comes already close to the ideal result but minor tweaking is still possible. If photographer and designer are different people, such a file format would make even more sense (to me).
If you think the idea further, one could come up with an image (metadata) format that lets the photographer define an ideal crop and a maximum and minimum crop he/she would be fine with. An example: For the following picture, the photographer wants definitely the branch on the left to not appear in the picture and the two grass blades on the right should definitely be inside the picture. A respective metadata format would allow the following:
Red means the minimal allowed crop and white the ideal crop. Green would be the real crop of the image in terms of throwing pixels away. It would leave the designer the opportunity to tailor the image to the layout while maintaining the artistic vision of the photographer. Even an almost square crop would be possible in this case (green as horizontal border and red as vertical border). I hope it is a bit more clear now.
Thanks for the hint, I will have a look and report back when/if I find something interesting/useful.
As I explained earlier, cropping is integral part of the raw development and cannot be separated. I would have to do the crop, revert the crop in darktable export and do a similar crop manually in scribus again. A cumbersome workflow that could be eased a lot by 4 numbers (coordinates) in the metadata if all the programs respect these 4 numbers.
I use exiftool for different purposes, but in this case the question is not how to add the metadata but how to make software aware of the metadata. First, I want to do the crop with a graphical frontend (I guess the reasons are quite obvious) and very early, that means in the raw developer (in my case darktable). When I do the crop the position information is already there, so it would be best to add the info in the darktable export. If @houz wouldn’t have been so kind to present the prospect of a darktable lua export solution, using exiftool to transfer the crop information from the raw’s xmp file to the exported jpeg with reverted crop would have been an option, but the discussion is for the remaining part of the process.
Best regards
Chris