Writing 10,12 bit TIFF files with LibTIFF C++

The TIFF specification does not specify a way to store 10, 12 or 14 bits per channel in an image. Depending on the encoder and decoder, it may still be possible to work with such images, but it is effectively an implementation detail, as they are not required to do this.

If you want more than 8 bits of precision in a TIFF, your only choice is 16 (or floating point, but that's a different story).

I'm not aware of any image format with specific support for these bitdepths, so viewers will likely be a problem anyway if you must store the image with that specific bitdepth. The simplest workaround I can think of would be to just store as 16 bits per pixel and put the original bitdepth as metadata (e.g. in an ImageDescription tag), but it all depends on what the images will be used for and why you need this information.