[23 Aug 2020, Timothy A. Gonsalves] Sensor spots removal, for Nikon photographers
Dust on the sensor is the bugbear of DSLRs. When changing a lens or even when a lens is zooming or focusing, it is very easy for a few tiny dust particles to sneak in. All DSLRs have a Sensor Clean function, but this is only partially effective. Professional cleaning of the sensor by a competent camera repair shop requires sending the camera to a nearby big city and costs thousands of rupees.
I had been using the Spot Removal tool in Lightroom or Darktable to manually remove the more obvious spots from images. This is tedious. Recently, I learnt how to remove all sensor dust spots from an image in one stroke. This works for most Nikon DSLRs.
In the Settings Menu, click "Image Dust Off Ref Photo"
Aim the camera at a plain white sheet or wall in good light and release the shutter
The camera stores a DSC0xxxx.NDF file -- this is a RAW file that contains only the sensor spots in a proprietary format! It cannot be viewed.
Download Nikon's Capture NX-D -- this is now free. It allows you to apply many camera settings on a RAW image post-facto.
In Capture NX-D, open any .NEF file that was shot after the .NDF dust off reference photo was saved
In the Edit panel, scroll to the Image Dust Off check box. If it is greyed out, click on "Change ..." below it and select the folder with the .NDF photo.
Now check the Image Dust Off box -- in a second or two, all the annoying sensor spots will disappear! If the result is not acceptable, uncheck the box and the spots will reappear.
Convert the .NEF to a suitable format for further processing.
Sample images before and after dust off are shown in the Table below. Note the spots in the lower left quadrant in the original. In the nospots image, the spots are almost completely gone. A couple of spots in the leaves have changed to an incorrect colour -- these need to be manually corrected.
Original with dust spots
Dust off by Capture NX-D
Right-click to view the image
One catch is that you have to shoot RAW images for Capture NX-D to do its trick. I set my D7200 to save RAW+JPEG Fine. Normally, I import the .JPG into LightRoom or DarkTable for classifying, minor editing, creating slideshows, etc. I save the .NEF (RAW) images in cloud.iitmandi and on a USB disk, then mostly forget about them.
Occasionally, if I find a good image with sensor spots, I load the .NEF into Capture NX-D, remove the sensor spots, save as a 16-bit .TIF, import into LR or DT and replace the .JPG.
It is advisable to use Settings>Clean Sensor regularly. Take an Image Dust Off Ref Photo after every time you clean the sensor.
If the light is insufficient or the sheet of paper is not sufficiently white, the camera may refuse to take a Dust Off Ref photo. The camera sets the focus to infinity so that any dirt on the lens is blurred and does not cause spots on the reference photo.
Capture NX-D will only use a .NDF that was shot before the .NEF that you wish to process. I tried to fool it by editing the EXIF data using exiftool, but without success.
Read this advice before attempting to clean your camera’s sensor: https://www.photo.net/learn/cleaning-your-dslr-sensor-tips-and-advice/
T.A. Gonsalves Sensor Dust Notes