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#11
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Hot pixels covered by warranty?
In message 0BrEf.741851$x96.570853@attbi_s72,
223rem wrote: This linear relationship does not hold. Hot pixels are already saturated. Huh? The RAW value of a hot pixel grows first above the average noise, and then increases as the exposure time is increased (or the ISO is raised). It goes through the whole range of potential RAW values before clipping at 4095, and reaching 4095 usually requires a pretty long exposure. The phenomenon is relative to global noise, and to signal. -- John P Sheehy |
#12
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Hot pixels covered by warranty?
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#13
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Hot pixels covered by warranty?
In message oLyEf.742411$x96.175858@attbi_s72,
223rem wrote: wrote: Huh? The RAW value of a hot pixel grows first above the average noise, and then increases as the exposure time is increased (or the ISO is raised). It goes through the whole range of potential RAW values before clipping at 4095, and reaching 4095 usually requires a pretty long exposure. The phenomenon is relative to global noise, and to signal. Even if they're not saturated, I doubt that the relationship is very linear. Do you mean that you believe even without clipping, signal alone plus hot-effect alone is not equal to the combined effect (disregarding random noise, of course)? -- John P Sheehy |
#14
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Hot pixels covered by warranty?
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#15
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Hot pixels covered by warranty?
In message OozEf.771598$xm3.418814@attbi_s21,
223rem wrote: wrote: Do you mean that you believe even without clipping, signal alone plus hot-effect alone is not equal to the combined effect (disregarding random noise, of course)? Right; the value of a hot pixel in an image is not equal to the value of the hot pixel in a "dark" control image + the correct pixel intensity in the image. In other words hot pixels are deffective; they dont merely have a different "zero" than other pixels. Well, that calls for some experiments, when I get the time. On the theoretical side, I would think that you should be able to profile all the pixels in a camera, at a given point in its life, and keep a record of blackpoint offsets (compared to average) for pixels and lines, and the individual sensitivities, and make a RAW bitmap at a higher bitdepth based on the *known* response of individual pixels. The only wild card would be the random elements. -- John P Sheehy |
#16
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Hot pixels covered by warranty?
Can we possible see an example of this "cluster" of hot pixels?
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#17
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Hot pixels covered by warranty?
223rem wrote:
In other words hot pixels are deffective; they dont merely have a different "zero" than other pixels. If the pixels work fine at brief exposures and grow more visible at longer exposures, they are "hot": charges are leaking into the well, and dark-frame subtraction should handle the matter fine (saturation notwithstanding). If the pixels are "defective", they just sit there at the same value no matter what the exposure or subject: the "erasure" is noted. A simple series of exposures will be informative: dark frames, start at 1s and go until about 2 minutes (or whatever your typical exposure is) in 1 stop increments. Look at the raw data for both your question pixels and what you deem to be ok pixels. |
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