Nikon Digital Camera Series
Nikon D2x – Creating and Using a Dust-Off Reference Photo
|© Darrell Young|
Dust bunnies are a fact of life, under the bed, and on your camera's CMOS or CCD imaging sensor. Users of Nikon Capture and Nikon's new digital SLR cameras have an exciting new way to deal with the problem.
We'll use the Nikon D2x as a reference point in this article, but the information applies to almost all of Nikon's digital SLR cameras, with a few differences in the menu selections and filenames. (The D1 is excluded, but not the D1x or D1h with firmware upgrades 1.10 or later – See footnote*)
Often, you may go out and do an exciting shoot, only to return and find that some dust spots have magically appeared in the worst possible place your images. If you then create a dust-off reference photo, you can simply use it to remove the dust spots from your images, and then go clean the sensor.
Here's how it works. When you use the instructions below to create the dust off reference photo, you will be shooting a blank unfocused picture of a pure white or gray background. The dust spots in the image will then be readily apparent to the Nikon Capture software. When you load the image to be cleaned into Nikon Capture, along with the dust-off image, it will use that image to remove the spots in your production image.
By learning to use the dust-off reference photo system you'll have a form of insurance against sneaky little dust bunnies. (They move around quickly, you know. Just try to catch one!)
Finding a Subject for the Reference Photo
First, we need to select a “featureless” subject to photograph for the reference photo. The key here is to use a material that has no graininess, such as bright white, slick plastic. I tried using plain white sheets of paper held up to a bright window, but the resulting reference photo was unsatisfactory to Nikon Capture 4.x. It gave me a message that my reference photo was “too dusty” when I tried to use it.
After some experimentation, I finally settled on three different subjects that seemed to work well:
Both of these provided enough light and featurelessness to satisfy both my camera and Nikon Capture. The key is to photograph something fairly bright, but not too bright. You may need to experiment with different subjects if you have no light table or computer.
Now, let's prepare the camera for the actual reference photo:
Menu Selections for Getting the Reference Photo
In Figure 1 you'll find the sequence of screens to prepare your camera for taking the photo.
While the screen in figure 1 is on your computers rear monitor, you will also find the word rEF in the viewfinder and top control panel. This simply means that we are ready to create the image.
Creating the Reference Photo
Once you have the camera ready, hold the lens about 4 inches (10 cm) away from the subject. The camera will not try to autofocus during the process, which is good, since you want the lens at infinity anyway. We are not trying to take a viewable picture, just create an image that shows where the dust is on the sensor. Focus is not important, and neither is minor camera shake. If you try to take the picture and the subject is not bright enough, or too bright, you will see the following screen (Figure 2).
If you don't see the screen in figure two, you have successfully created a dust off reference photo. You will find the following image on your camera monitor. (Figure 3) A two-megabyte file is created on your camera's image card with an ending of .NDF instead of the normal .NEF, .TIF, or .JPG. This NDF file is basically a small database of the millions of clean pixels in your imaging sensor. (Example filename: DSC_1234.NDF)
You cannot display it on your computer. It will not open in Nikon Capture or any other graphics program that I tried.
Now, copy the .NDF file from your camera's memory card to its own folder on your computer's hard drive, so that you can use it the next time you want to remove new dust spots from your sky pictures. Keep this folder for dust reference images, and give it a name that will help you remember what the files are later. I called my folder DustOffRef .
Now we're ready to move into Nikon Capture and use our new reference photo on some images.
At the end of this article you will find information about this reference file for early Nikon DSLRs. (See footnote*)
Using the Reference Photo in Nikon Capture
Load Nikon Capture and then open an image within it. We will do a test on this image. You might want to do a File … Save As… and save the image under a name like TestImage.NEF, or use a junk image, just in case we damage it.
Now that we have an image open in Capture, let's use our reference photo. First, let's make sure Nikon Capture has Tool Palette # 2 open, since that is where we select our reference photo.
Click the View menu in Nikon Capture, and make sure that the “Show Tool Palette 2” selection has a check mark to the left of it. (See Figure 4)
Scroll down on Tool Palette 2 until you find the Image Dust Off tool just above the Vignette tool. (See Figure 5) Be sure to check the checkbox so that a green checkmark appears next to the Image Dust Off title, instead of a red X. Here is a screenshot of what you'll see:
Now, we are ready to load our reference photo and use it to check the test photo we have already loaded into Capture. Click the Change… button in the Image Dust Off tool, and use the Browse for Folder window that opens to find the location of your dust reference photo. As mentioned earlier, I have mine saved on my computer's C: drive in a folder named DustOffRef . (See Figure 6) Once you've located the folder containing your NDF reference photo, just click OK.
Nikon Capture will now apply the dust-off reference photo to the current image. You should see the dust spot disappear. The process will take a minute or so, and there will be a message window open with a progress bar to keep you informed.
The dust reference photo information (date and time) will now show up in the Image Dust Off tool. See Figure 7 for example.
At this point, the process is complete, and your image has been cleaned.
If, after selecting a dust reference folder containing the dust-ref image (figure 6), you see a warning that the dust-off photo does not closely match the current image, you can probably choose to continue. I have seen no problems with detail loss due to any “mismatch” between the dust-off image and the image to be cleaned. In Figure 8, you'll see the message that pops up with a mismatch.
It may be a good idea to create several dust-off images. Create each image in similar light to the ones you want to clean. From the message in Figure 8, it seems that Nikon Capture will select whichever image is the best match for the image to be cleaned.
Nikon has truly given us a powerful and convenient tool to keep our images looking their best. This feature alone makes it worth purchasing the USD $100 Nikon Capture program. Use this cool Nikon Capture tool to keep your images looking the best they can be!
Keep on capturing time…
|Footnote: * Creating Dust Off Ref Photos with D1-Series and D100 Cameras|
In addition to D2-series, D200, D70s, D70, and D50 cameras, Dust Off ref photos can be taken with the D1x / D1H (firmware version 1.10 or later), and D100. Dust Off ref photos can not be created with the D1 or with earlier versions of the camera firmware for the D1x and D1H. Dust Off ref photos taken with the D100, D1x, or D1H have the extension “.nef”; do not change this extension.