Grayscale from color

I have PDF images with many colors and have used convert to change them
to grayscale.
 
My problem is that the original images contain large chunks of yellow
text and linework and when this yellow converts to grayscale the yellow
portions are very light gray indeed.
 
I think that what I need to do is to change all yellow graphics to black
and then convert the resultant image to grayscale. I don't know how to
do this and would appreciate advice from your users.
 
Thanks you.
 

Ian Hall
GIS Co-ordinator

East Gippsland Water
P 03 5150 4433
F 03 5150 4477
E [email protected] <mailto:[email protected]> 
W www.egwater.vic.gov.au <http://www.egwater.vic.gov.au/> 

 

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