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General / Re: Historical Aerial georectification and mosaic optmial workflow assistance
« on: January 08, 2016, 03:34:53 PM »
I ran a very small pilot project looking at a couple of scanning options for large volumes of negatives. I only had 4 negatives, but I'd also received a set of 9 images that had been previously scanned, as well as individually georeferenced versions of these. Some early notes here: http://www.agisoft.com/forum/index.php?topic=3790.msg19777#msg19777 and a model created from these https://skfb.ly/F9FE
In the end I used an image template of the fiducial marks to manually position the scans, and a Photoshop action to add an alpha mask and apply radial lightening.
16bit scans worked better than 8 bit scans. Best results were obtained when max,min pixel values were ~90%,10% respectively (much less noise)
The 9 prescanned images I received were also scanned on an Epson and I ran them through the equivalent workflow even though they were only 8bit and exhibited obvious curling on some images. As they supplied geotiff versions of these as well I was able to redo the georeferencing of the raw scans. The results I got from Photoscan were better than the supplied georeferenced images.
The biggest problem with the Epson 10000XL (or V700) for large negatives is that you need to find something to flatten the negatives with. Curling negatives can create significant distortion.
In the end I used an image template of the fiducial marks to manually position the scans, and a Photoshop action to add an alpha mask and apply radial lightening.
16bit scans worked better than 8 bit scans. Best results were obtained when max,min pixel values were ~90%,10% respectively (much less noise)
The 9 prescanned images I received were also scanned on an Epson and I ran them through the equivalent workflow even though they were only 8bit and exhibited obvious curling on some images. As they supplied geotiff versions of these as well I was able to redo the georeferencing of the raw scans. The results I got from Photoscan were better than the supplied georeferenced images.
The biggest problem with the Epson 10000XL (or V700) for large negatives is that you need to find something to flatten the negatives with. Curling negatives can create significant distortion.