[magick-users] monochrome?

[Bob Friesenhahn]

On Tue, 17 Sep 2002, Phlip wrote:

> Magick-ians:
>
> Suppose I have a vibrant color picture (or even a b-w ink drawing scanned in
> full color) called image.ppm:
>
> 	convert image.ppm -monochrome out.ppm
>
> After that runs, I need to see in out.ppm a pure black-and-white picture.
> Just as if I had scanned with the "lineart" feature.
>
> Here are the awesome ImageMagick features I don't need:
>
>  - dithering of pixels to simulate grays

Use +dither to disable that.

>  - the two "monochrome" colors mapped to the most
>       frequent dark and light grays
>
> I need ImageMagick to take each color pixel, average its RGB together, and
> send everything below middle gray to black and everything above to white.
>
> I have tried the threshold option but its results were inconclusive.

Threshold can be quite useful.  It is important to know that with the
default ImageMagick build, the default range for threshold is 0-65535
so using

  -threshold 32768

Would delineate at the mid-point of the range.

Bob
======================================
Bob Friesenhahn
bfriesen at simple.dallas.tx.us
http://www.simplesystems.org/users/bfriesen