[magick-users] How to reduce 24 bit color picture.bmp file 15 bit color picture file.

[Au Kum Chuen]

Hi,
 
I have picture files in 24 bit color and would like to reduce the number
of color bits to 15 bits.
How to I use imagemagick to do it? 

The reason I need to reduce the number of bits is that I need to display
a normal bmp file on PC to a small device which only has 15 bits of
color (5 red, 5 green, 5 blue). 
I tried writing my own program to remove the least 3 bits to get 8 bits
to 5 bits but the end result is 
some sharp change in color in areas for what should be a gradual change
of color tone. 
I understand that dithering is a possible help to my problem. I would
know how to get imagemagick to do it.

I have seen examples on how to reduce the number of colors to 16 or 256
to fit a GIF file, and there was
mention of a way to convert to 16 bit color space but there no example
was given. 

I hope some one can point me a way out.
 


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