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Hot pixels on a Canon 300D

 
 
Nick
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      11-17-2003
I just bought a Canon EOS 300D and, being the paranoid type, immediately ran
deadpixeltest.exe on it. I took the pictures using the RAW setting with the
lens cover on. And at 5 seconds or more, it finds this group of pixels:

http://members.chello.se/nscho/bad_pixels.gif

It seems strange that there should be a whole bunch of hot pixels so close
to each other. And no, it's no compression artifact, they really look like
this on the RAW image.

I'm not very likely to take too many pictures using more than 5 seconds, but
the fact that they are all clustered together bothers me. So what do you
think, is it a bad sensor, or can something else cause this?



 
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jriegle
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      11-17-2003
No, that is not a compression artifact. Even in RAW, the camera still has to
"blend the pixels" or thin lines will get color artifacts since it has a
Bayer sensor.. You are simply seeing the effect of "hot" red sensing cell.
The software that blends the pixels together and softens the image somewhat
causes this in the outpu image.

It is often missunderstood that RAW means "right off the sensor". That is
not the case.
John

"Nick" <(E-Mail Removed)> wrote in message
news:Lmcub.3692$%W3.19960@amstwist00...
> I just bought a Canon EOS 300D and, being the paranoid type, immediately

ran
> deadpixeltest.exe on it. I took the pictures using the RAW setting with

the
> lens cover on. And at 5 seconds or more, it finds this group of pixels:
>
> http://members.chello.se/nscho/bad_pixels.gif
>
> It seems strange that there should be a whole bunch of hot pixels so close
> to each other. And no, it's no compression artifact, they really look like
> this on the RAW image.
>
> I'm not very likely to take too many pictures using more than 5 seconds,

but
> the fact that they are all clustered together bothers me. So what do you
> think, is it a bad sensor, or can something else cause this?
>
>
>



 
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Mr Blobby
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      11-18-2003
Is that what's causing the red dots in this 15-20 Min exposure ?
http://www.users.bigpond.com/andrewc...uth%20Pole.htm
I originally thought they were Geostationary satellites !

Andrew


"jriegle" <(E-Mail Removed)> wrote in message
news:s6dub.278492$(E-Mail Removed)...
> No, that is not a compression artifact. Even in RAW, the camera still has

to
> "blend the pixels" or thin lines will get color artifacts since it has a
> Bayer sensor.. You are simply seeing the effect of "hot" red sensing cell.
> The software that blends the pixels together and softens the image

somewhat
> causes this in the outpu image.
>
> It is often missunderstood that RAW means "right off the sensor". That is
> not the case.
> John
>
> "Nick" <(E-Mail Removed)> wrote in message
> news:Lmcub.3692$%W3.19960@amstwist00...
> > I just bought a Canon EOS 300D and, being the paranoid type, immediately

> ran
> > deadpixeltest.exe on it. I took the pictures using the RAW setting with

> the
> > lens cover on. And at 5 seconds or more, it finds this group of pixels:
> >
> > http://members.chello.se/nscho/bad_pixels.gif
> >
> > It seems strange that there should be a whole bunch of hot pixels so

close
> > to each other. And no, it's no compression artifact, they really look

like
> > this on the RAW image.
> >
> > I'm not very likely to take too many pictures using more than 5 seconds,

> but
> > the fact that they are all clustered together bothers me. So what do you
> > think, is it a bad sensor, or can something else cause this?
> >
> >
> >

>
>



 
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chibitul
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Posts: n/a
 
      11-18-2003
In article <Lzdub.15004$(E-Mail Removed)>,
"Mr Blobby" <(E-Mail Removed)> wrote:

> Is that what's causing the red dots in this 15-20 Min exposure ?
> http://www.users.bigpond.com/andrewc...uth%20Pole.htm
> I originally thought they were Geostationary satellites !
>
> Andrew


Geostationary satellites are all in the equatorial plane of the Earth,
since they *have to* rotate at the same speed with the Earth to appear
geostationarry to us... thus they have to be in the equator plane, not
north or south of this unique plane. Your hot pixels are all ober the
place!
 
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Vadim
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Posts: n/a
 
      11-18-2003
It won't answer your question exactly, but you can find very useful
information on hot pixels here:
http://webpages.charter.net/bbiggers...ot_pixels.html


"jriegle" <(E-Mail Removed)> wrote in message news:<s6dub.278492$(E-Mail Removed)>...
> No, that is not a compression artifact. Even in RAW, the camera still has to
> "blend the pixels" or thin lines will get color artifacts since it has a
> Bayer sensor.. You are simply seeing the effect of "hot" red sensing cell.
> The software that blends the pixels together and softens the image somewhat
> causes this in the outpu image.
>
> It is often missunderstood that RAW means "right off the sensor". That is
> not the case.
> John
>
> "Nick" <(E-Mail Removed)> wrote in message
> news:Lmcub.3692$%W3.19960@amstwist00...
> > I just bought a Canon EOS 300D and, being the paranoid type, immediately

> ran
> > deadpixeltest.exe on it. I took the pictures using the RAW setting with

> the
> > lens cover on. And at 5 seconds or more, it finds this group of pixels:
> >
> > http://members.chello.se/nscho/bad_pixels.gif
> >
> > It seems strange that there should be a whole bunch of hot pixels so close
> > to each other. And no, it's no compression artifact, they really look like
> > this on the RAW image.
> >
> > I'm not very likely to take too many pictures using more than 5 seconds,

> but
> > the fact that they are all clustered together bothers me. So what do you
> > think, is it a bad sensor, or can something else cause this?
> >
> >
> >

 
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Kevin McMurtrie
Guest
Posts: n/a
 
      11-18-2003
In article <Lmcub.3692$%W3.19960@amstwist00>, "Nick" <(E-Mail Removed)>
wrote:

> I just bought a Canon EOS 300D and, being the paranoid type, immediately ran
> deadpixeltest.exe on it. I took the pictures using the RAW setting with the
> lens cover on. And at 5 seconds or more, it finds this group of pixels:
>
> http://members.chello.se/nscho/bad_pixels.gif
>
> It seems strange that there should be a whole bunch of hot pixels so close
> to each other. And no, it's no compression artifact, they really look like
> this on the RAW image.
>
> I'm not very likely to take too many pictures using more than 5 seconds, but
> the fact that they are all clustered together bothers me. So what do you
> think, is it a bad sensor, or can something else cause this?
>
>
>


That's a hot pixel. The width is probably due to some software blurring
to avoid Bayer pattern aliasing.

Here's a 19.3 minute exposure:

http://www.pixelmemory.us/Photos/Out...t%2022%202003%
20Star%20Spin/CRW_0142.CRW

Or it's reduced JPG:
http://www.pixelmemory.us/Photos/Out...t%2022%202003%
20Star%20Spin/spin.jpg

(The red line is a laser from the Lick Observitory)


That's really not too many hot pixels for 19 minutes. They could even
be masked with a threshold based filter. Yeah, it's touch blurry. It's
windy up there and I haven't gotten around to upgrading my tripod yet.
 
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Mr Blobby
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Posts: n/a
 
      11-18-2003
Thanks for that, does that mean they follow the planets line ?

"chibitul" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
> In article <Lzdub.15004$(E-Mail Removed)>,
> "Mr Blobby" <(E-Mail Removed)> wrote:
>
> > Is that what's causing the red dots in this 15-20 Min exposure ?
> > http://www.users.bigpond.com/andrewc...uth%20Pole.htm
> > I originally thought they were Geostationary satellites !
> >
> > Andrew

>
> Geostationary satellites are all in the equatorial plane of the Earth,
> since they *have to* rotate at the same speed with the Earth to appear
> geostationarry to us... thus they have to be in the equator plane, not
> north or south of this unique plane. Your hot pixels are all ober the
> place!



 
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Phil
Guest
Posts: n/a
 
      11-18-2003


Kevin McMurtrie wrote:

> In article <Lmcub.3692$%W3.19960@amstwist00>, "Nick" <(E-Mail Removed)>
> wrote:
>
>
>>I just bought a Canon EOS 300D and, being the paranoid type, immediately ran
>>deadpixeltest.exe on it. I took the pictures using the RAW setting with the
>>lens cover on. And at 5 seconds or more, it finds this group of pixels:
>>
>>http://members.chello.se/nscho/bad_pixels.gif
>>
>>It seems strange that there should be a whole bunch of hot pixels so close
>>to each other. And no, it's no compression artifact, they really look like
>>this on the RAW image.
>>
>>I'm not very likely to take too many pictures using more than 5 seconds, but
>>the fact that they are all clustered together bothers me. So what do you
>>think, is it a bad sensor, or can something else cause this?
>>
>>
>>

>
>
> That's a hot pixel. The width is probably due to some software blurring
> to avoid Bayer pattern aliasing.


I'm not sure I agree. My first 300D had a true, undeniable hot pixel --
and it showed up at all exposure speeds, even 1/1000 sec. And it was
visible as a bright point in all images where it was in an area with a
darkish background (e.g., grass).

A nunber of factors MAY result in apparent hot pixels with long exposures:

o How warm was the camera/CMOS when the test was done?

o Was there light leakage from the viewfinder (i.e., was the VF cover
supplied with the camera in place)?

I was also curious at what file was tested in DeadPixelTest. The
versions I've used deal with jpeg or tiff, but not RAW. What file was
really tested.

So I'm not quite ready to conclude that this is a "hot pixel" situation
... vs. noise or light leakage or a conversion artifact.

Phil

 
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Dave Martindale
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Posts: n/a
 
      11-18-2003
"Mr Blobby" <(E-Mail Removed)> writes:
>Thanks for that, does that mean they follow the planets line ?


I don't think so. The geostationary satellites all have to be in the
Earth's equatorial plane. The planets are (mostly) found in the solar
system's plane. But the earth's axis of rotation is tilted 23 degrees
with respect to the solar system's plane, so the 2 planes are separated
by that much angle.

Dave
 
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Mr Blobby
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Posts: n/a
 
      11-18-2003
Doh !


Of course !

Thanks.


"Dave Martindale" <(E-Mail Removed)> wrote in message
news:bpcmm8$1pt$(E-Mail Removed)...
> "Mr Blobby" <(E-Mail Removed)> writes:
> >Thanks for that, does that mean they follow the planets line ?

>
> I don't think so. The geostationary satellites all have to be in the
> Earth's equatorial plane. The planets are (mostly) found in the solar
> system's plane. But the earth's axis of rotation is tilted 23 degrees
> with respect to the solar system's plane, so the 2 planes are separated
> by that much angle.
>
> Dave



 
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