[magick-users] Transparency issue

[Jorge]

Hi,

I need to make transparent some zones in an image but not others that have 
the same color. For example if I take logo: image (the ImageMagick wizard), 
I want to turn transparent all white zones but not the white beard.

In other words, I want to make transparent the background of an image but 
not the inner zones that have same color as background is.

I try to use Masking Simple Backgrounds (floodfill) example from Anthony 
Thyssen's example page http://www.imagemagick.org/Usage/channels/

Below the DOS script:
convert logo: ( +clone -fx "p{0,0}" ) -compose 
ifference  -composite  -modulate 100,0  +matte  difference.png

convert difference.png  -threshold 0  boolean_mask.png

convert logo:  boolean_mask.png +matte -compose CopyOpacity -composite 
logo_boolean.png

but the beard turn transparent...!

Can anyone help me?

Thanks in advance.

Jorge Colaccini