Are all of these dead pixels or noise?

mtux · 04-05-2014, 09:18 PM

See the attached photo! It's a 100% cropped in near center of a long exposure photo taken with K30 and DA21ltd.
Can you see those red, green, ... pixels! Are they dead pixels? so many!? or noise? You see I've put the NR of LR5 to 50! so some level of NR is done to it.

Any thought or advice is appreciated.

Attached Images

severalsnakes · 04-05-2014, 09:23 PM

You might look into "hot" pixels. As I understand it, "hot pixels" are basically just blown out pixels that can show up during long exposures and/or high ISOs? I had a bunch crop up during a trip to the zoo when I took a lot of pictures in very very low light in some nocturnal exhibits. They are not permanently damaged pixels and they "reset" themselves after a short period of time. I am no technical expert (obviously), but you mentioned it was a long exposure, so this could be the same "hot pixel" problem.

elliott · 04-05-2014, 09:28 PM

That is an extremely long exposure, 3.5 minutes, hot pixels are inevitable. I'm assuming you didn't use dark frame subtraction in the body, that can help a lot. It takes a second exposure for the same duration with the shutter closed to map the hot pixels.

mtux · 04-05-2014, 09:32 PM

Originally posted by Steve.Ledger

What was to ISO used?

Check the photo, it's stated there

ISO100!

Originally posted by severalsnakes

but you mentioned it was a long exposure, so this could be the same "hot pixel" problem.

Well, yes that's 211seconds, I thought hot pixels are same as dead pixels.

---------- Post added 04-06-14 at 12:33 PM ----------

Originally posted by Steve.Ledger

Too blurry to tell. Looks like a load of dust.

Colorful dusts!?

I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.

severalsnakes · 04-05-2014, 09:34 PM - **2 Likes**

Originally posted by mtux

I thought hot pixels are same as dead pixels

Nope!

Check out this link: Dead vs Stuck vs Hot Pixels

elliott · 04-05-2014, 09:42 PM

Originally posted by mtux

I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.

What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.

severalsnakes · 04-05-2014, 09:46 PM

Originally posted by elliott

What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.

And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable.

Still not sure the issues you're having are the same ones I had at the zoo...

mtux · 04-05-2014, 10:06 PM

Originally posted by elliott

What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.

You are right, and this was the first time for me to play with some ND filters, so I wasn't quite sure what I'm gonna get! it was mostly experimental.

Originally posted by severalsnakes

And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable.

I'm not afraid of that at all, and when I need to I go up to 3200, Here as I mentioned above it was mostly experimenting as long as possible shutter speed.

Steve.Ledger · 04-05-2014, 10:20 PM

Originally posted by mtux

Check the photo, it's stated there

ISO100!

Yeh, sorry - was right in front of my face and I missed it - hence I removed the post, sorry it was too late for you to not see

Quote:

Colorful dusts!?

I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.

Well yes, why not coloured dust? Should all dust be white???
If you have three ND filters in front of the lens then there's 6 more surfaces for dust to have collected and F11 might be just right to pick it up.

Anyway, I'm probably wrong was just a thought.

mtux · 04-05-2014, 10:24 PM

Originally posted by Steve.Ledger

If you have three ND filters in front of the lens then there's 6 more surfaces for dust to have collected and F11 might be just right to pick it up.

But dust particles should be bigger than one pixel! aren't they!? and since this is a 100% shot, those dots are only 1 pixel of the sensor!

Thanks guys for ideas and help.
Well I check another photo from that night which is around 120sec long, and these aren't visible there. so it should be the hot pixel which kicks in at this exposure time. and this should be the reason that NR doesn't help!

But how should we get rid of them? is there any way?

elliott · 04-05-2014, 10:41 PM

Originally posted by mtux

But how should we get rid of them? is there any way?

I know nothing about Lightroom, but Darktable has a tool specifically for hot pixels that does pretty well.

Steve.Ledger · 04-05-2014, 11:13 PM

Lightroom should remove bright / hot pixels automatically.
Your screenshot is blurry and those dots are certainly bigger than 1 pixel in that. How about making your original file available for better answers and suggestions?

TenZ.NL · 04-05-2014, 11:56 PM

Originally posted by severalsnakes

And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable.

Still not sure the issues you're having are the same ones I had at the zoo...

I don`t think that`s such a good idea for long exposures, as increased ISO creates more heat in the sensor. The same goes for the extended time the shutter is open during long exposures, so those 2 add up.
Noise is usually directly related to heat.

Adam · 04-06-2014, 12:45 AM - **1 Like**

Originally posted by mtux

See the attached photo! It's a 100% cropped in near center of a long exposure photo taken with K30 and DA21ltd.
Can you see those red, green, ... pixels! Are they dead pixels? so many!? or noise? You see I've put the NR of LR5 to 50! so some level of NR is done to it.

Any thought or advice is appreciated.

Enable slow long shutter speed noise reduction and this won't happen. I recommend having it on for exposures longer than 30 seconds.

maltfalc · 04-06-2014, 07:31 AM - **1 Like**

Originally posted by TenZ.NL

I don`t think that`s such a good idea for long exposures, as increased ISO creates more heat in the sensor. The same goes for the extended time the shutter is open during long exposures, so those 2 add up.
Noise is usually directly related to heat.

why would increased iso heat up the sensor? as far as i know, changing iso just changes how the camera interprets the signal from the sensor. if anything, with long exposures a higher iso should mean less heat because of the shorter exposure.

04-05-2014, 09:18 PM	#1
mtux Veteran Member Join Date: Apr 2013 Location: the Netherlands Photos: Gallery \| Albums Posts: 2,444	Are all of these dead pixels or noise? See the attached photo! It's a 100% cropped in near center of a long exposure photo taken with K30 and DA21ltd. Can you see those red, green, ... pixels! Are they dead pixels? so many!? or noise? You see I've put the NR of LR5 to 50! so some level of NR is done to it. Any thought or advice is appreciated. Attached Images

04-06-2014, 12:45 AM - 1 Like	#14
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Originally posted by mtux See the attached photo! It's a 100% cropped in near center of a long exposure photo taken with K30 and DA21ltd. Can you see those red, green, ... pixels! Are they dead pixels? so many!? or noise? You see I've put the NR of LR5 to 50! so some level of NR is done to it. Any thought or advice is appreciated. Enable slow long shutter speed noise reduction and this won't happen. I recommend having it on for exposures longer than 30 seconds. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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04-05-2014, 09:23 PM	#2
severalsnakes Veteran Member Join Date: Jan 2013 Location: Kansas City, KS Photos: Gallery Posts: 1,612	You might look into "hot" pixels. As I understand it, "hot pixels" are basically just blown out pixels that can show up during long exposures and/or high ISOs? I had a bunch crop up during a trip to the zoo when I took a lot of pictures in very very low light in some nocturnal exhibits. They are not permanently damaged pixels and they "reset" themselves after a short period of time. I am no technical expert (obviously), but you mentioned it was a long exposure, so this could be the same "hot pixel" problem.

04-05-2014, 09:28 PM	#3
elliott Inactive Account Join Date: Dec 2008 Location: North Carolina Photos: Albums Posts: 1,720	That is an extremely long exposure, 3.5 minutes, hot pixels are inevitable. I'm assuming you didn't use dark frame subtraction in the body, that can help a lot. It takes a second exposure for the same duration with the shutter closed to map the hot pixels.

04-05-2014, 09:32 PM	#4
mtux Veteran Member Join Date: Apr 2013 Location: the Netherlands Photos: Gallery \| Albums Posts: 2,444 Original Poster	Originally posted by Steve.Ledger What was to ISO used? Check the photo, it's stated there ISO100! Originally posted by severalsnakes but you mentioned it was a long exposure, so this could be the same "hot pixel" problem. Well, yes that's 211seconds, I thought hot pixels are same as dead pixels. ---------- Post added 04-06-14 at 12:33 PM ---------- Originally posted by Steve.Ledger Too blurry to tell. Looks like a load of dust. Colorful dusts!? I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.

04-05-2014, 09:34 PM - 2 Likes	#5
severalsnakes Veteran Member Join Date: Jan 2013 Location: Kansas City, KS Photos: Gallery Posts: 1,612	Originally posted by mtux I thought hot pixels are same as dead pixels Nope! Check out this link: Dead vs Stuck vs Hot Pixels

04-05-2014, 09:42 PM	#6
elliott Inactive Account Join Date: Dec 2008 Location: North Carolina Photos: Albums Posts: 1,720	Originally posted by mtux I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens. What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.

04-05-2014, 09:46 PM	#7
severalsnakes Veteran Member Join Date: Jan 2013 Location: Kansas City, KS Photos: Gallery Posts: 1,612	Originally posted by elliott What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better. And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable. Still not sure the issues you're having are the same ones I had at the zoo...

04-05-2014, 10:06 PM	#8
mtux Veteran Member Join Date: Apr 2013 Location: the Netherlands Photos: Gallery \| Albums Posts: 2,444 Original Poster	Originally posted by elliott What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better. You are right, and this was the first time for me to play with some ND filters, so I wasn't quite sure what I'm gonna get! it was mostly experimental. Originally posted by severalsnakes And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable. I'm not afraid of that at all, and when I need to I go up to 3200, Here as I mentioned above it was mostly experimenting as long as possible shutter speed.

04-05-2014, 10:20 PM	#9
Steve.Ledger Veteran Member Join Date: Oct 2009 Location: Far North Qld Posts: 3,301	Originally posted by mtux Check the photo, it's stated there ISO100! Yeh, sorry - was right in front of my face and I missed it - hence I removed the post, sorry it was too late for you to not see Quote: Colorful dusts!? I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens. Well yes, why not coloured dust? Should all dust be white??? If you have three ND filters in front of the lens then there's 6 more surfaces for dust to have collected and F11 might be just right to pick it up. Anyway, I'm probably wrong was just a thought.

04-05-2014, 10:24 PM	#10
mtux Veteran Member Join Date: Apr 2013 Location: the Netherlands Photos: Gallery \| Albums Posts: 2,444 Original Poster	Originally posted by Steve.Ledger If you have three ND filters in front of the lens then there's 6 more surfaces for dust to have collected and F11 might be just right to pick it up. But dust particles should be bigger than one pixel! aren't they!? and since this is a 100% shot, those dots are only 1 pixel of the sensor! Thanks guys for ideas and help. Well I check another photo from that night which is around 120sec long, and these aren't visible there. so it should be the hot pixel which kicks in at this exposure time. and this should be the reason that NR doesn't help! But how should we get rid of them? is there any way?

04-05-2014, 10:41 PM	#11
elliott Inactive Account Join Date: Dec 2008 Location: North Carolina Photos: Albums Posts: 1,720	Originally posted by mtux But how should we get rid of them? is there any way? I know nothing about Lightroom, but Darktable has a tool specifically for hot pixels that does pretty well.

04-05-2014, 11:13 PM	#12
Steve.Ledger Veteran Member Join Date: Oct 2009 Location: Far North Qld Posts: 3,301	Lightroom should remove bright / hot pixels automatically. Your screenshot is blurry and those dots are certainly bigger than 1 pixel in that. How about making your original file available for better answers and suggestions?

04-05-2014, 11:56 PM	#13
TenZ.NL Veteran Member Join Date: Feb 2012 Location: Below sealevel Photos: Gallery \| Albums Posts: 1,100	Originally posted by severalsnakes And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable. Still not sure the issues you're having are the same ones I had at the zoo... I don`t think that`s such a good idea for long exposures, as increased ISO creates more heat in the sensor. The same goes for the extended time the shutter is open during long exposures, so those 2 add up. Noise is usually directly related to heat.

04-06-2014, 07:31 AM - 1 Like	#15
maltfalc Veteran Member Join Date: May 2010 Location: Winnipeg Photos: Albums Posts: 396	Originally posted by TenZ.NL I don`t think that`s such a good idea for long exposures, as increased ISO creates more heat in the sensor. The same goes for the extended time the shutter is open during long exposures, so those 2 add up. Noise is usually directly related to heat. why would increased iso heat up the sensor? as far as i know, changing iso just changes how the camera interprets the signal from the sensor. if anything, with long exposures a higher iso should mean less heat because of the shorter exposure.