LibRaw do not care about in-camera crops like 16:9 and always returns full image.
So, if you want to completely repeat Adobe DNG convertor behavior, you need to parse Exif/makernotes metadata (and, possibly, add vendor-specific or camera-specific hints).
AFAIK, Adobe default cropping is because of
- let some space for demosaic (so ignore pixels very close to border)
- let some space for sensor positioning errors (seen in some cameras, within several pixels)
- also, physical masking may produce border effects (like diffraction) close to mask edge.
LibRaw do not care about in-camera crops like 16:9 and always returns full image.
So, if you want to completely repeat Adobe DNG convertor behavior, you need to parse Exif/makernotes metadata (and, possibly, add vendor-specific or camera-specific hints).
AFAIK, Adobe default cropping is because of
- let some space for demosaic (so ignore pixels very close to border)
- let some space for sensor positioning errors (seen in some cameras, within several pixels)
- also, physical masking may produce border effects (like diffraction) close to mask edge.