What happen to my camera?


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daohuay

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May 10, 2006
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#1
I notice that my 40D show some bright spot when i take picture with long shutter. :cry:
Is that dust?
How do i clean it?
 

#2
If you don't have any photo as a reference. No one is going to know what you are talking about. And you never mentioned you shot it in the day or night or indoor. What you means by long shutter and whatever. If you want feedback to help you solve the problem you need to provide more details.
 

DiGdUb

Senior Member
Apr 24, 2006
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#3
most probably hot pixels.
 

daohuay

New Member
May 10, 2006
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Jurong West
#5
I'm sorry, I'm so worried that I forget to provide details.

I shoot without lens and the picture is totally black.

this is the picture


In RAW, the spots is in red and green color.
In Jpeg, it's white.
 

spazzer

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May 5, 2007
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BUKIT PANJANG
#6
I'm sorry, I'm so worried that I forget to provide details.

I shoot without lens and the picture is totally black.

this is the picture


In RAW, the spots is in red and green color.
In Jpeg, it's white.
to me it seems like a issue with dust on your sensor.... not very sure about that :confused:
 

spazzer

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May 5, 2007
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#7
to me it seems like a issue with dust on your sensor.... not very sure about that :confused:
u can try sending it to canon service center if u are not sure how to clean cause u may damage the mirror if u are not experienced and that could be costly
 

Apr 12, 2005
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#8
I'm sorry, I'm so worried that I forget to provide details.

I shoot without lens and the picture is totally black.

this is the picture


In RAW, the spots is in red and green color.
In Jpeg, it's white.
From your description, it's most probably hot pixels if they only appear after long exposure.

In RAW, they appear in red/green/blue because each photosite collects lights only for Red or Green or Blue. For jpeg, each pixel colour is a processed value using an array of values collected from RGB photosites and therefore appear grey/white.

Turn on the Noise Reduction for long exposure on your camera to get them mapped out and removed for that picture.

Hot pixels are normal and nothing to worry about.

Do a search on hot pixels to learn more.

In contrast, stuck pixels are bright pixels which are always there regardless of exposure time and they need to be mapped out permanently.
 

daohuay

New Member
May 10, 2006
339
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Jurong West
#9
From your description, it's most probably hot pixels if they only appear after long exposure.

In RAW, they appear in red/green/blue because each photosite collects lights only for Red or Green or Blue. For jpeg, each pixel colour is a processed value using an array of values collected from RGB photosites and therefore appear grey/white.

Turn on the Noise Reduction for long exposure on your camera to get them mapped out and removed for that picture.

Hot pixels are normal and nothing to worry about.

Do a search on hot pixels to learn more.

In contrast, stuck pixels are bright pixels which are always there regardless of exposure time and they need to be mapped out permanently.
Thank you Clockunder for ur enlightenment.
I have try turning on Noise Reduction and it's works!!
Is there other way than Turn on the Noise Reduction? The Noise Reduction process will take the same amount of time as the exposure.
 

Apr 12, 2005
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#10
Thank you Clockunder for ur enlightenment.
I have try turning on Noise Reduction and it's works!!
Is there other way than Turn on the Noise Reduction? The Noise Reduction process will take the same amount of time as the exposure.
Hot pixels arise from signal interferences generated by thermal energy aka heat on the image sensor due to long exposure. The longer the shutter speed, the more hot pixels can be expected.

What long exposure noise reduction does is taking another frame of the scene with the shutter closed for the same duration (i.e. if the shutter speed for the original is 30 seconds, then another frame would also be 30 seconds) immediately after the shot to find out the locations of any the bright pixels and then use this information to map out the hot pixels. (With the shutter closed, the whole frame is expected to be near black and any bright pixels still present are therefore long exposure noise ........ aka hot pixels.). As can easily be deduced from the above, this mapping of hot pixels is the most effective way of reducing/eliminating unwanted long exposure noise.

If you do not use long exposure NR, you would need a lot of time to clone out obvious hot pixels in post-processing and I don't think there is any easier way than long exposure NR.

(p.s. hot pixels are very frequently confused with stuck pixels which are permanent in nature and are there regardless of shutter speed. Hot pixels are nothing to worry about while stuck pixels need to be mapped out permanently through pixel mapping (Olympus DSLR has it as a feature in the camera while other brands need to be sent to the service centre to have them mapped....i.e. their locations identified and their values to be permanently replaced by an averaging algorithm using values from adjacent photosites.).
 

daohuay

New Member
May 10, 2006
339
0
0
Jurong West
#11
Hot pixels arise from signal interferences generated by thermal energy aka heat on the image sensor due to long exposure. The longer the shutter speed, the more hot pixels can be expected.

What long exposure noise reduction does is taking another frame of the scene with the shutter closed for the same duration (i.e. if the shutter speed for the original is 30 seconds, then another frame would also be 30 seconds) immediately after the shot to find out the locations of any the bright pixels and then use this information to map out the hot pixels. (With the shutter closed, the whole frame is expected to be near black and any bright pixels still present are therefore long exposure noise ........ aka hot pixels.). As can easily be deduced from the above, this mapping of hot pixels is the most effective way of reducing/eliminating unwanted long exposure noise.

If you do not use long exposure NR, you would need a lot of time to clone out obvious hot pixels in post-processing and I don't think there is any easier way than long exposure NR.

(p.s. hot pixels are very frequently confused with stuck pixels which are permanent in nature and are there regardless of shutter speed. Hot pixels are nothing to worry about while stuck pixels need to be mapped out permanently through pixel mapping (Olympus DSLR has it as a feature in the camera while other brands need to be sent to the service centre to have them mapped....i.e. their locations identified and their values to be permanently replaced by an averaging algorithm using values from adjacent photosites.).
wow, thank you for sharing the technology behind NR. I can just use NR for reducing unwanted long exposure noise/ hot pixels?
Do u recommend to service/mapping my camera bcos of hot pixels?:think:
 

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