Anthony Thyssen schrieb:
> Stephan Hennig on  wrote...
> | 
> | Converting bluebells_darker.jpg to grey scale alone returns an image
> | with 255 colours:
> | 
> | convert bluebells_darker.jpg -colorspace Gray grey.png
> | 
> | I can't believe the best approximation of this image with 254 colours
> | should result in 16 colours, but with IM it does:
> | 
> | convert grey.png -colors 254 grey254.png
> | 
> prehaps you should use a Q16 version of IM instead of Q8
> this has a higher quality internally, in which case you get a larger
> variable of the greyscaling operation, for the quantization to play
> with, and thus a finer control.

That seemed to do the trick.  With the Q16 version -colors works as
expected on grey scale images.  Thank you for your helpful comments!

Best regards,
Stephan Hennig

PS:  Though, I'm still wondering why Q8 fails so bad.  Shouldn't 24 bit
be enough to reduce the number of colours of simple grey scale images?
I can't see any reason this operation hits Q8's limits.

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