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11-02-2020, 04:27 PM   #1
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Hot/ Dead pixels in CMOS vs CCD Cameras?

I've been taking some long exposures recently with my K-S2, and I've noticed a handful of "hot" pixels. Nothing bad, nothing worrisome, just enough to get me curious.

I had thought a hot pixel was "on" all the time, but I only see these fellas get weird after 1s or longer of exposure. For a "normal" shot—1/125s, ISO 400—they appear to function normally. I had a few hot pixels in my K100D-Super, and they were always on. Mostly green pixels. One was blue, and one was orange (I didn't think sensors had actual orange pixels?). But they were always on, even at quick exposures such as 1/500s, ISO 100.

So, my question: if these pixels on my K-S2 still perform adequately for most of my shots, should I run the "Pixel Mapping" option on my K-S2? Will doing so permanently deactivate these pixels? Does Pixel Mapping have any effect on RAW capture?

Can't stress this enough, we're talking about five or six pixels on a 20MP CMOS sensor. If I ever needed to create a pixel-perfect image, it'd be the easiest Photoshop fix in the world.

11-02-2020, 04:58 PM - 2 Likes   #2
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QuoteOriginally posted by PocketPixels Quote
I've been taking some long exposures recently with my K-S2, and I've noticed a handful of "hot" pixels. Nothing bad, nothing worrisome, just enough to get me curious.

I had thought a hot pixel was "on" all the time, but I only see these fellas get weird after 1s or longer of exposure. For a "normal" shot—1/125s, ISO 400—they appear to function normally. I had a few hot pixels in my K100D-Super, and they were always on. Mostly green pixels. One was blue, and one was orange (I didn't think sensors had actual orange pixels?). But they were always on, even at quick exposures such as 1/500s, ISO 100.

So, my question: if these pixels on my K-S2 still perform adequately for most of my shots, should I run the "Pixel Mapping" option on my K-S2? Will doing so permanently deactivate these pixels? Does Pixel Mapping have any effect on RAW capture?

Can't stress this enough, we're talking about five or six pixels on a 20MP CMOS sensor. If I ever needed to create a pixel-perfect image, it'd be the easiest Photoshop fix in the world.
For longer exposures, slow shutter speed noise reduction (aka dark frame subtraction) is generally the way to go, as some hot pixels (due to heat) will inevitably show up. Pixel mapping will help with pixels that are permanently broken, but that's a different thing.

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11-02-2020, 05:14 PM   #3
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For long exposures there will always be some hot pixels for some reason. I would just let software take care of it. Most Raw developers have a feature for hot pixels.
11-02-2020, 05:39 PM   #4
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You can either turn on dark frame subtraction or you can shoot a dark frame in the same conditions (lens cap on, same exposure length and iso) for all the shots in the same conditions.

11-02-2020, 06:49 PM   #5
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Not too surprising with long exposures. Depending on what you are doing with the long exposures using the in camera slow shutter noise reduction will resolve it, but in other cases you might be better served by creating a master dark for the session and subtracting that but that only really becomes something to consider if doing lots of long exposure shots like when doing astrophotography, night panoramas, or night landscapes where you may be stacking or combining images.
11-02-2020, 07:39 PM   #6
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Other than turning on slow shutter noise reduction (which effectively doubles your exposure time), keeping your ISO low as possible will limit the heat buildup and reduce the amount of hot pixels. It may prevent them all together, depending on other variables. If possible, open up your aperture so you can use a lower ISO and/or quicker shutter speed.
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