<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">After much effort, I obtained an old set of 1928-1930 USGS topo maps of Oʻahu Island, Hawaiʻi - for a project I am working on. The maps are without collars and used by a local archaeological firm. The geotiff maps at first showed as completely black on my Mac system (10.10.5 - Yosemite). However I found this link with a resultuion for the issue:<div class=""><br class=""></div><div class=""><a href="http://stackoverflow.com/questions/13925995/options-to-convert-16-bit-image" class="">http://stackoverflow.com/questions/13925995/options-to-convert-16-bit-image</a></div><div class=""><br class=""></div><div class="">I opened the 16 quads for Oʻahu in Photoshop and applied auto levels, after which they became discernable quad maps. However, when imported into QGIS, they are now invisible. I wonder if it is possible that I stripped away the geotiff CRS information. Prior to the Photoshop operation, the maps did appear correctly referenced to Oʻahu Island (although they were totally opaque / black).</div><div class=""><br class=""></div><div class="">Now, the maps in QGIS are not visible, although the geotiffs are several megabytes in size and are visible when opened in Photoshop, Preview, or whatever image viewer. </div><div class=""><br class=""></div><div class="">I should mention that I have successfully imported other sets of USGS maps of Oʻahu for this project - the 1902 series, the 1916 series, the 1935 series - as well as the current series. The early maps used the Old Hawaiian CRS (EPSG 3564) but more modern maps use WGS83, Zone 4N (EPSG 3711). I have on the fly projection enabled and have tried many CRS settings for the maps, but nothing results in a visible quad appearing.</div><div class=""><br class=""></div><div class="">Suggestions very welcome ...</div></body></html>