I am georeferencing scanned historical maps (RGB-tif). After rectification the images show spurious nodata pixels, usually the darkest parts of inscriptions. In the original file these pixels are not tagged as nodata so somehow during the rectifying process ArcGIS 'decides' to set these pixels to nodata.
I have tried different options in the rectify menu but to no avail.
To make things more clear I have attached two images: