The Nikon star eater

Another way to get rid of hot pixels is to check for pixels that differ drastically from their immediate neighbors. The rationale is that genuine details in the image will always spill over from one pixel to another, so if a pixel is bright all by itself, it must be "hot" and should be eliminated.

The Nikon D40, D50, D70, D70s, D80, and related DSLRs do this automatically, in the camera, even before saving the raw image, and it has an unfortunate side effect: it eats stars. That is, sharp star images tend to be removed as if they were hot pixels (Figure 2.1).

There is a workaround. Turn on long-exposure noise reduction, set the image mode to raw (not JPEG), take your picture, and then, while the camera is taking the second exposure with the shutter closed, turn the camera off. This seems like a foolish thing to do, but actually, a "truly raw" image has already been stored on the memory card. If you let the second exposure finish, that image will be replaced by one processed by the star eater. By powering the camera off, you keep this from happening. This workaround is popularly known as Mode 3 (see also p. 35).

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