Stop OCR Changing Photo Contrast

How can I stop Acrobat Pro 10.1.16 (Mac version) from changing contrast of photos when I run OCR on a PDF scan?

I'm scanning with a Fujitsu SnapScan ix500 document scanner, and prefer the photo scans within text I get from it.

But when I open the scan in Acrobat Pro to run OCR (which also straightens text on page),

the contrast of photos is increased which makes many areas of photos go black and lose detail.

I'm selecting "Aa in this file" from "Recognize Text" in the Tool panel.

Are there settings that I can change to control what that action does?
If so where? how?

I'm looking in Preferences but all I see so far is "Color Management" which has "North America General Purpose 2" select for "Settings:".