Convert image to black and white

OmniGraffle OmniGraffle for Mac
4

If I were you, I’d first open the image in Preview*, then use Tools: Adjust Color (Cmd-Alt-C) and drag to Saturation to 0. Then just Cmd-C again, and paste into OmniGraffle.

* Launch Preview, then Cmd-N to open the image that’s on the clipboard.

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