Please help! spots on photos

[icassell]

I see the spots on the re-post. I guess you could try and get a monitor with matched dead pixels ...

 

[Bifurcator]

Would magic-marker work if I'm on a CRT?

 

[Battou]

Would magic-marker work if I'm on a CRT?

Only if applied to the glass

 

[manaheim]

I see the spots. "I see dead pixels" hehehe... It's pretty bad too. Those are weak, semi-dead, and dead cells for sure.

It really is actually a problem with the D100 and long exposures. It just does this. I should pull up one of my older uncorrected night shots and post it.

 

[Bifurcator]

All CCDs do this. At least all the ones I've owned. That's kind of allot too.

I dunno exactly what it is but it has something to do with exposure times, and amplification, and probably in camera processing too. Usually times of around 1sec and over and lower amplification like <400 ISO. I've been told that it's "weak or partially dead cells" which I suppose could mean several things on a technical level.

I never seem to see this on CMOS images so I guess this is specific to CCD sensors.

 

[Bifurcator]

Here it is in the Konica/Minolta A2 just for reference:

Cheaper (or older?) sensors have more dots in. I think shooting the sun allot adds them too but I haven't confirmed that.

 

[ann]

i have a d100 and have never had a "hot pixel", must be lucky (and yes i have done a lot of long time exposures.

they can be removed in post processing

 

[Bifurcator]

I had to turn off noise reduction and do a triple exposure to get those to show. In some uncommon exposure settings you'll see it. If your camera is BRAND SPANKING NEW and you just happened to get a lucky CCD batch it's possible that there are none - for the 1st few thousand shots.

I wish I knew more technical information about it - I could actually explain it instead of just proclaiming it.

 

[manaheim]

I had to turn off noise reduction and do a triple exposure to get those to show. In some uncommon exposure settings you'll see it. If your camera is BRAND SPANKING NEW and you just happened to get a lucky CCD batch it's possible that there are none - for the 1st few thousand shots.

I wish I knew more technical information about it - I could actually explain it instead of just proclaiming it.

Taken from here:

"low light (night photos or dark scenes): when the scene is dark the amount of light measured by each pixel of the CCD is low. When the light intensity is very low it can become too close to the level of noise naturally found in the CCD. In such cases some pixels can appear as noise because the noise level measured for them is significantly close or higher than the actual light intensity.

slow shutter speeds: when the shutter is kept open for a long time more noise will be introduced to the photo. A slow shutter speed translates to the CCD integrating more light per pixel. The effect can be easily understood as the CCD &#8220;accumulating" light in each pixel and measuring the total light over the shutter period of time. However at the same time the CCD is also &#8220;accumulating" noise. For that reason in slow shutter speed photos some pixels will appear as noise because for these pixels the amount of noise integrated is significantly close to or higher than the actual light measured."

Someone... (I think it was Garbz) actually gave a scientific description of what caused this at one point. It's buried in the forums somewhere.

 

[Bifurcator]

Yeah, in the "How is noise created?" thread. But that has all to do with random noise and not to do with certain specific cells that act semi-dead or that consistently become over-bright in some rare exposure conditions. Right? Or did I misunderstand what you said?

I'm pretty sure this is related to whatever the technical explanation is for a dead pixel. It's just "dead" in one or two colors and/or not completely dead in those. <shrug>

 

[manaheim]

Well... I guess I don't think that his sensor has dead pixels. Basing this off experience with my own D100... I got noise on all my long shots, but they were NOT in the same place all the time, so it really was kinda random noise.

BTW, I have also seen something that said that long exposures created heat on the CCD, which caused some kind of voltage irregularity, resulting in a erroneous color representation on pixels here and there... but I didn't find that reference in my 10 seconds of googling.

I do have my D100 sitting here. I suppose I could go take some sample shots... how bored do I feel?

*manaheim fiddles with his D100 for the first time in months*

JESUS this screen is small. Yikes. BTW, the feature I was talking about is "Long Exposure Noise Reduction". It's in the menu denoted by a Pencil icon... at least I think thats a pencil... that's a REALLY TEENY screen.

 

[Bifurcator]

Well... I guess I don't think that his sensor has dead pixels. Basing this off experience with my own D100... I got noise on all my long shots, but they were NOT in the same place all the time, so it really was kinda random noise.

His are (all in the same place) and so are mine. I'm talking about those not any of the random noise that was also present.

And you're right, they aren't "dead" completely... they only act dead in some circumstances. Since they're always in the same place it's not noise - though I guess it could be the affects of noise on some weak or partially dead cells.

BTW, I have also seen something that said that long exposures created heat on the CCD, which caused some kind of voltage irregularity, resulting in a erroneous color representation on pixels here and there... but I didn't find that reference in my 10 seconds of googling.

That makes sense and sounds interesting.

BTW, the feature I was talking about is "Long Exposure Noise Reduction". It's in the menu denoted by a Pencil icon... at least I think thats a pencil... that's a REALLY TEENY screen.

Right, that's what clears out the noise and leaves the semi-dead pixels still sitting there.

 

[manaheim]

His are (all in the same place) and so are mine. I'm talking about those not any of the random noise that was also present.

Oh, they are? Hm. Ok, I missed that part. I'm bad at detail sometimes.

And you're right, they aren't "dead" completely... they only act dead in some circumstances. Since they're always in the same place it's not noise - though I guess it could be the affects of noise on some weak or partially dead cells.

Yeah, could be.

Right, that's what clears out the noise and leaves the semi-dead pixels still sitting there.

Well, it's not the same noise reduction as on my D300... on the D300 it's an algorythm. On the D100 it takes two pictures. Oh shoot, I just remembered I told the OP (who has probably abandoned us to another one of our back and forths by now ) that the first exposure was of the same scene... it's not.

On the D100 it takes a picture of blackness... I believe it does this by leaving the curtain in place. It then looks at that and calculates where the off pixels are. Then it takes a second picture of the scene, compares the two and makes a final image.

That would also suggest that the manufacturer was expecting the "off" pixels to remain in the same location, which probably means that I was wrong about my bad pixels being in different locations. They were probably in the same spot each time. Again... detail... me... not always good friends. :mrgreen:

Really, I blame age.

 

[Bifurcator]

NP... it's all good. It's fun to talk about this stuff - for me. Probably annoying to people who just want a quick fix and don't care about why.

But yeah, because all CCDs (but not CMOS) that I know of, exhibit these "problems" the black photo for mapping them out is common across allot of different cameras. Now mostly these days it's in the camera software that comes with the camera and for CMOS models is still useful for the occasional dust spec that decides it wants to mess up a photo session.

 

[manaheim]

heheh, yup it is fun. It's why I'm on here way too much.

Welp... le'ts go mangle another thread.