Autocrop of raw-files?

Processing
1

Hi,
I am still working on digitizing my slide-collection by taking pictures of the slides within the slide projector. I am using an Olympus OM-D with MFT sensor and aspect ration 4:3. My installation of camera and slide projector simplifies the positioning of the slides in left/right direction in contrast to up/down. But the positioning of up/down must not be perfect because there is a lot of “waste” of shooting the 2:3 slides by the 4:3 camera sensor.

Disadventage: a large black frame above and below the slide which must be cropped.

Actually I am using the “trim”-command of imagemagick to autocrop the jpg-photos by a batch script. The size of slides varies so I have to use a rather large shave border to reduce a manual rework. In the meanwhile I try some other (own) cropping algorithms using ImageJ-plugins in combination with batch scripts.

Now my questions:
Is there a possibility to autocrop raw-files? I am using digiKam, Rawtherapee and Darktable for the raw-processing. I haven’t found a kind of autoremoving black borders (besides of imagemagick-trim).
Is there an easy possibility to use own code in these programs? The usage of own plugins in ImageJ is really cool.

Best regard,
Markus

2

I’d imagine any of the command line tools of dt or RT would do it, if you can specify a constant crop window that’ll work for each image.

I’m getting ready to do a similar exercise, and what I’m thinking of doing is putting some sort of marker in the slide holder that I can use to register the slide when I insert it. It’d show up in the capture, but I could use it with one capture to manually determine the top-left, for instance, and build my crop window with that. Maybe a needle taped to the diffusion screen…