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As a consultant to contractors, I receive PDFs of architectural drawings to use as backgrounds in CAD.

Some are scanned copies, some are grey-scale and, if lucky, some are black and white. I use GIMP to convert the scans and grey scales to PNGs.

What procedure should I use to minimize speckles when I scale the drawing up by 96 times in CAD?

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marked as duplicate by Scott, Yisela Aug 24 '13 at 20:20

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

The above question only has an answer for Photoshob (but the procedures are similar in GIMP). Also see: How to remove gray background on gray picture? for GIMP, and How can I remove the unwanted background from a scanned handwritten signature? for different approaches. –  Takkat Aug 24 '13 at 8:55

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