D600 Vs 6d...Wide-Field Astrophotography

Started Feb 14, 2013 | Discussions thread
Marianne Oelund
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A brief history of Nikon hot-pixel suppression
In reply to mpe, Feb 16, 2013

mpe wrote:

Is the well known problem with RAW median cut noise suppression that can't be disabled finally solved in recent Nikon DSLRs? If not Canon is better choice.

Depends on what you mean by "solved."  It is still there, but is now in its third generation, which is a considerable improvement over the first.

The purpose and function is to remove hot pixels; it isn't a median or averaging noise filter.  In the D3 generation, since it was applied indiscriminately to all data in the raw file, it did have some noise-reduction effect, even though that wasn't its purpose.  It also had a very narrow span of action, resulting in deletion or distortion of star images.

For the D7000, Nikon improved the algorithm by using adjacent other-channel values when deciding on what level to reassign a "hot" pixel to.  This avoided the "donut star" problem and reduced the probability of unintentionally removing star images.

In the D4/D800 generation, it has become more sophisticated and is applied selectively rather than generally.  I have more detail in some old emails which I could look up; Bernard Delley and I collaborated in studying the latest algorithm, and he came up with a good simulation of it.

All versions of the algorithm, however, are limited in that they cannot remove hot pixels that are in close proximity to each other.  Thus you may still find pairs or clusters of hot pixels remaining in the image.  The Capture NX 'astro' filter apparently deals with these.

In the D4, HPS is only applied for exposure times exceeding 1 second.  In other cameras such as the D800/E, the threshold is 1/4 sec or longer.

There are some sample image files available from my website at http://actionphotosbymarianne.com/Tech if you would like to see how the different generations of HPS work.

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Qualities possessed by God in infinite proportion: Love, Grace, Power, Righteousness, Wisdom, . . .
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- Marianne

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