Long Shtr NR - off, what to do on PC?

[F1L1P]

The other day I shot some pics using long exposure, but the Long shutter noise reduction was set to off, because I did not want to see that counter after each photo being taken. So, now I have JPEG and RAW both with unwanted hot pixels on my image.

What can we do if we do not want to waste our time waiting for NR to finish in camera?

Today I did a test. I put lens cap on to simulate pitch black, and took 2 shots:
Hot pixels on 60 sec exposure(JPEG, Long Shtr NR - off):

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Hot pixels on 122 sec exposure(JPEG, Long Shtr NR - off):

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The real problem is when you open RAW file (Long Shtr NR - off, same pic as above JPEG, 122 sec exposure)

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now imagine you are shooting beautiful beach at night, clear sky...and you get this over your image

How can this be fixed on PC?

 

[Djarum]

The one's in the Raw image almost look like stuck pixels, not hot pixels.

I wonder when the remapping pixel function is done, it only works for jpegs?

I have no idea of how to remove them from the raw.

 

[F1L1P]

The one's in the Raw image almost look like stuck pixels, not hot pixels.

I wonder when the remapping pixel function is done, it only works for jpegs?

I've tried pixel mapping, and nothing.
Could you do this and see if you'll get the same results?
Turn on you camera, don't remove lens cap, set to bulb mode and take one RAW+JPEG image.

 

[GaryCh]

Interesting...

I shall have to try this test myself.

It should be easy to write some software to take a "lens-cap-on-long-exposure" and note the hot pixels into a profile for that sensor/camera.

Later, you would be able to run the software against a folder of images and it would recalculate each hot pixel using its neighour-average - or you could interactively "brush away" hot pixel grains from photographs on an individual basis to avoid fudging more pixels than we must.


Would such software be useful to anyone ? If so I shall try to find a copy of the file format for RAW images and see what I can come up with.


-Gary

 

[ampan]

Does "Long Shtr NR" effect RAWs ?

 

[Brianetta]

Does "Long Shtr NR" effect RAWs ?

It certainly does on the Olympus PEN. I'd be interested to know if Panasonic did it the same way.

What can we do if we do not want to waste our time waiting for NR to finish in camera?

If all of your photos are part of a shoot in very similar conditions at approximately the same time, I'd suggest that you take a dark frame (your lens cap, perhaps) for reference at the beginning and end of your shoot, and if it's a long shoot then perhaps one or two during. This saves you time, because the camera isn't taking one every single time you make an exposure. One per exposure is most accurate, but I agree that waiting for a minute or two after each shot can be a real drag.

Once this is done, you can apply the dark frame to your images back on your PC. ufraw has a special field for applying a dark frame for noise reduction, so your raw processors may well have one as well. You might want to try several of your dark frames, until you find one wher ethe noise matched most closely.

Even if you just shoot JPEG, you can use this trick: here is a Gimp tutorial on the subject.

If you didn't shoot at least one dark frame, then you're going to have to approach this differently. Shooting a new dark frame at a different temperature with different charge levels on your sensor is going to give poor results. If you have no dark frame, but do have two photos taken at about the same time but reframed (even slightly), then you might be able to use the photos as noise references for each other, especially in dark or very low contrast areas of the image.

 

[ChristopheG]

Good tricks given by the following comments, really good experments.