Stephan Hennig on wrote...
| 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.
|
It is a matter of having enough 'play' in the memory size so that the
dither can work correctly.
The dither needs to have a larger color value to correctly work, in its
color registers, and these are set to the same size as the Q level used
to save the image in memory. Without it the color just go straight from
maximum to minimum without any chance to differentiate things.
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
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Anthony's Home is his Castle http://www.cit.gu.edu.au/~anthony/
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