Hot pixels covered by warranty?

Should I bother asking Canon to change the sensor of my 20D
due to the presence of a cluster of hot pixels? It really becomes
noticeable at long exposure times (of the order of seconds) in
night shots. It sounds like nothing, but it is annoying to find
a red blob in a night shot.

thanks.

223rem wrote:

Should I bother asking Canon to change the sensor of my 20D
due to the presence of a cluster of hot pixels? It really becomes
noticeable at long exposure times (of the order of seconds) in
night shots. It sounds like nothing, but it is annoying to find
a red blob in a night shot.

Changing the sensor will just move the hot pixels around. Don't waste
your time at Canon, do this instead:

www.google.com: dark frame subtraction

wrote:
223rem wrote:


Should I bother asking Canon to change the sensor of my 20D
due to the presence of a cluster of hot pixels? It really becomes
noticeable at long exposure times (of the order of seconds) in
night shots. It sounds like nothing, but it is annoying to find
a red blob in a night shot.


Changing the sensor will just move the hot pixels around. Don't waste
your time at Canon, do this instead:

www.google.com: dark frame subtraction


I guess that means that you subtract a "dark" image
(obtained by taking a photo with the lens cap on) from the
image you want to clean. The problem is that hot pixels become
hotter with increased exposure time, so you have to match the
exposure times before subtraction, which is a big pain in the
ass.

Another problem is that it seems that it is not just an isolated
hot pixel, but a cluster (although that could be an artifact--the
result of transforming the raw image into jpeg). One isolated
pixel I can accept, but not a blob!

223rem wrote:

I guess that means that you subtract a "dark" image
(obtained by taking a photo with the lens cap on) from the
image you want to clean. The problem is that hot pixels become
hotter with increased exposure time, so you have to match the
exposure times before subtraction, which is a big pain in the
ass.

Well, if you think it'll be easier to hassle Canon, then who am I to
stop you? But if you want quality long-exposure images you gotta
subtract properly collected and processed darks, even if you manage to
get Canon to give you a new sensor.

Another problem is that it seems that it is not just an isolated
hot pixel, but a cluster (although that could be an artifact--the
result of transforming the raw image into jpeg). One isolated
pixel I can accept, but not a blob!

When you do the dark-frame subtraction, the computer does the
arithmetic per pixel. All 8 million of them, independently. It
doesn't matter where the hot pixels are, how they are clustered, etc.

I guess the other concern must be "Will the issue get any worse" - possibly
leaving you in a situation with an unusable camera, and out of warranty.

wrote:

When you do the dark-frame subtraction, the computer does the
arithmetic per pixel. All 8 million of them, independently. It
doesn't matter where the hot pixels are, how they are clustered, etc.

Dark frame subtraction will set the hot pixels to 0. With or without
it, N scattered hot pixels affect the image less than N hot pixels grouped
in a blob.

"223rem" wrote in message
news:TTeEf.769702$xm3.663619@attbi_s21...
Should I bother asking Canon to change the sensor of my 20D
due to the presence of a cluster of hot pixels? It really becomes
noticeable at long exposure times (of the order of seconds) in
night shots. It sounds like nothing, but it is annoying to find
a red blob in a night shot.

First, manufacturers won't replace the sensor if it has hot pixels; they
will simply reprogram the camera to ignore the pixels.

Second, if hot pixels are showing up only on long time exposures, that's
normal and there's nothing wrong to begin with. It's the nature of digital
photography.

223rem wrote:

wrote:

When you do the dark-frame subtraction, the computer does the
arithmetic per pixel. All 8 million of them, independently. It
doesn't matter where the hot pixels are, how they are clustered, etc.

Dark frame subtraction will set the hot pixels to 0.

image(hot pixel value) = thermal noise + signal
dark(hot pixel value) = thermal noise

image(hot pixel value) - dark(hot pixel value) = signal

You will only get a hole if the dark hot pixel is saturated, and you
get less signal if the image hot pixel is saturated. I'd recommend you
actually try the procedure, but you appear to be dead-set to hassling
Canon. Carry on!

wrote:

image(hot pixel value) = thermal noise + signal
dark(hot pixel value) = thermal noise

image(hot pixel value) - dark(hot pixel value) = signal


This linear relationship does not hold. Hot pixels are already
saturated.

I'll give it a try though, as I dont hold any hope in Canon.

"Ryan Robbins" wrote in message
news:ThhEf.5927$J81.5177@trndny01...

Second, if hot pixels are showing up only on long time exposures, that's
normal and there's nothing wrong to begin with. It's the nature of digital
photography.

For me, the keyword was "cluster" of hot pixels - not a "number" of hot
pixels. That bit's definately not normal.