[gthumb-list] can't view some NEF files

[Nathan <sirrahn gmail com>]

Hi, can someone help me? I am new to gthumb and am trying to view NEF files taken with a Nikon camera. However, some of the images do not show in gthumb and only an icon is displayed. For these images the information on the image says it is Format:TIFF. The ones that show correctly are listed as RAW format. I'm sure they are all raw!

I am also using darktable and the items were also catalogued by Shotwell until I got rid of it. I don't think that all the photos that are not showing have be edited in darktable.  

If anyone can help I'd really appreciate it because gthumb looks like just what I want, but I need it to see all the photos.