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

wrote:
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.

Even if they're not saturated, I doubt that the relationship is
very linear.

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

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.

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

Can we possible see an example of this "cluster" of hot pixels?

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.