Threshold slider whec converting to black and White

[James M]

There is a black and white convert feature in Corel Photopaint that I would like to find, make, or figure out an equivalent way of doing in xnview. You start with a color image, and the converter brings up a typical filter dialog, with the before and after image boxes. The conversion type I specify is called "line art" and it gives me a threshhold slider. The slider determines what is considered white and what is black.
It does a great job of taking images that have shading as well as linear features that are various colors, and making the linear features black and dropping the shading. Its like an edge detect with a "darker-lighter" adjustment.
This kind of thing is great for converting USGS, or "topo" maps, to black and white for use in Autocad.
I can program in VB but not C.
Any advice on how to accomplish the line art convert in xnview is greatly appreciated.

[xnview]

There is a black and white convert feature in Corel Photopaint that I would like to find, make, or figure out an equivalent way of doing in xnview. You start with a color image, and the converter brings up a typical filter dialog, with the before and after image boxes. The conversion type I specify is called "line art" and it gives me a threshhold slider. The slider determines what is considered white and what is black.
It does a great job of taking images that have shading as well as linear features that are various colors, and making the linear features black and dropping the shading. Its like an edge detect with a "darker-lighter" adjustment.
This kind of thing is great for converting USGS, or "topo" maps, to black and white for use in Autocad.
I can program in VB but not C.
Any advice on how to accomplish the line art convert in xnview is greatly appreciated.

Currently you can convert in BW, but the threshold can be changed, i'll change that...

[James M]

wow, great! hey, which of the five "methods" of converting to BW would you do this for?
I should mention the ones that produce "screened" conversions are not really useful for what I am doing, I need one that attempts to make either solid black lines, or nothing. I would be happy to send some examples of the before and after I am looking for. Its the least I should do for anyone willing to spend time on this.
thanks