15

Excitingly, these terms mean different things to different people. I think the most useful distinction is like this: Stuck pixels are always completely bright, as if they're fully overexposed Dead pixels are always off, as if receiving no light (these are usually less obvious) Hot pixels are not permanently stuck, but show up during long exposures (as the ...


11

It is called a stuck pixel, because it seems to be stuck all the way on in every image. To be more precise, it a red pixel that seems to be stuck all the way on. When the camera or RAW convertor program converts the information from the sensor, the high value of that one pixel is also causing the surrounding pixels to have artificially high red values ...


10

You can't really prevent hot pixels on long exposures, you can only deal with them. For a single four minute exposure the easiest way is to use what is known as Dark Frame Subtraction. Different manufacturers have different names for in camera versions of it. Canon, the brand I shoot, calls it Long Exposure Noise Reduction. After an image is taken the ...


10

For exposures longer than 1 second, you can enable Long Exposure Noise Reduction (LENR). This is Canon's nomenclature for in-camera dark frame subtraction. When you take a photo the camera will expose the image normally and then use the same settings to create a dark frame with the shutter left closed. The readings for each pixel in the dark frame will be ...


5

Most consumer digital cameras nowadays do automatic dark frame subtraction, which should hide any stuck pixels. (Actually, just plain subtraction would only make the pixel black instead of red, but pretty much all decent dark frame correction algorithms also detect stuck pixels and interpolate over them.) In fact, the automatic dark frame subtraction is ...


5

Ideally, dark frame subtraction should be done with raw images before demosaicing. Then the resulting black spot is 1 pixel, and after demosaicing it will typically be invisible in the result due to the interpolation during processing. You seem to have used converted (jpeg?) files, in which the stuck (hot) pixels have already been smeared over the ...


3

It's near impossible to tell exactly what the spots in your picture are. It is fairly easy to look at them and eliminate what they are not: hot or dead pixels. Due to the sharp outlines and well defined irregular shapes of the different spots it is fairly safe to say that they are on or very close to the actual sensor itself, and not on top of the stack of ...


3

I'll explain the image stacking method here. Image stacking can yield better results, you then take multiple images at lower ISO and/or expose for a shorter time. A practical way to go about this is to just take the first picture at a high ISO and expose for long enough until you see the details you want to see, but possibly with a lot of noise and a lot of ...


2

Hot pixels in a sensor boil down to slight differences in the "response" of each photodiode, as resulting from the manufacturing process. Silicon, the semiconductor used in CMOS manufacture, is a "doped" medium. It is a silicon base that has been mixed with a slight amount of impurities in order to support that "semi" conductivity. The distribution of ...


2

One of the main causes is exposure to radiation (e.g. it is more likely to get hot pixels when travelling by airplane vs travelling by ship). Edit: Okay, this was the description for LCDs (view old edits). For camera sensors this is mainly caused by leakage currents, which are electric charges leaking into sensor wells. The ADC interprets this as a high ...


2

Based on the position of the red dots in between the building, they appear to be radio towers. That is a typical configuration for the aircraft warning lights on two parallel antennas and I think the antenna itself may also be visible, but it's hard to tell at that detail level. My guess is that the red blotch is also something accurate to what was there, ...


2

That is what a hot or stuck pixel looks like when it is so "hot" that the fully saturated signal from one pixel figures prominently into the interpolated values of surrounding pixels when the data from the sensor is demosaiced to create colors from the monochromatic luminance values captured by each pixel well on the sensor. If it is a hot pixel the way to ...


2

With any image sensor you will get some hot pixels and these will be noticeable in long exposures - but easily fixed in post processing. Unfortunately what is a 'normal' amount is very subjective, most sensor manufacturers do mention a percentage of pixels that may or may not work as no manufacturing process is 100% perfect, the more well known manufacturers ...


2

These are irregular shapes and my guess is that they are not pixels, but drops of some purple liquid. If you set your camera to the cleaning mode, remove the lens and inspect your sensor with loupe and a flashlight. When you try to locate the spot on the sensor, don't forget that the image is recorded upside down.


2

Hot pixels are pixels that read out at full voltage/saturation as a result of heat in the sensor. Once the sensor is allowed to cool they will usually return to their proper state and read out a voltage value based on the amount of light that has struck the pixel well the next time they are used. They most often present an issue during long and/or high ISO ...


1

What is the difference between hot, stuck, and dead pixels? Dead pixels are stuck in the off state (totally dark), while hot pixels are stuck in the on state (they stay on). What can cause each to occur? Hardware problems. You could think of a dead pixel on a video screen like a blown light bulb -- it just doesn't work any more. Image sensors are sort ...


1

The "radio towers" in the upper left quadrant of the first image appear to be ghosting. The pattern in the upper left quadrant is an inverted and flipped version of the brightest lights at the corresponding spot in the lower right quadrant of the photo. For an easier to visualize example and a fuller explanation please see is it normal to get significant ...


1

The last paragraph is very important - would they be hot pixels, you will see them in the black image as well. If you rule out reflections, laser toys, UFOs and other sources outside of camera, it must be inside ;) See the article http://www.astrophys-assist.com/educate/noise/noise.htm covering the physical sources of noise on CCD and how to treat them. ...


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