Magick++ bitdepth for monochrome BMP

[xdaiana]

Hello folks,

I cannot manage to transform a monochrome tiff loaded from disk in an Image object into a bitmap with 1 bit per pixel.
I'm using Magick++, not the command line tool.
I tried with

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image.depth(1)

also with

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image.type(BilevelType)

when getting the depth it was correct, but after writing the image on disk

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image.write("bla.bmp")

the image had 24 bits per pixel.

Is there any restriction that I'm missing? Because from command line it worked...

Thank you
Daiana

[xdaiana]

seems that setting the depth does not function at all
I managed to reduce bitdepth using quantize, but as far as I understood this function always optimizes the depth, so if I'm asking for a RGB image but the input content is B/W or grayscale I will not get the resulting bitdepth I need.