Extreme pixel peeping

Started Dec 3, 2008 | Discussions
bg2b Contributing Member • Posts: 897
Extreme pixel peeping

Has anyone noticed the black dots that sometimes appear to the side of extreme highlights in 5dii pictures? I saw this mentioned in a thread on photo.net ( http://photo.net/canon-eos-digital-camera-forum/00RewZ ;), but I'm finding it in some of the samples here too.

It seems to happen on shots processed with DPP and ACR, and in camera JPEGs, so I don't think it's any sort of artifact from one converter. It appears more prevalent at higher ISOs, but even at ISO 100 or 200, you can sometimes find it.

I collected together some crops from various samples that I've seen posted here and elsewhere. I believe this sample includes photos from five different cameras, and the crops are all shown at 200%. I apologize for the extreme level of pixel peeping, but when thinking about shelling out that much for a camera, not to mention lenses, I want to at least know more about it. In particular, how universal is it, and if it's not just a case of a few bad cameras, is it fixable in firmware or software?

Badgerh Regular Member • Posts: 468
Can you see it at 100%

If not it is probably a software issue in scaling up the images.

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OP bg2b Contributing Member • Posts: 897
Re: Can you see it at 100%

Yes, you can see it at 100%. The 200% is just to make it clearer in the crops; no interpolation was done in scaling up.

DSPographer Senior Member • Posts: 2,483
Yikes

I hadn't noticed this in the samples I looked at. How common is it? It sure looks like a variation of the "black sun" effect that sometimes happens with CMOS sensors.

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stewartde Forum Member • Posts: 58
Chromatic Aberration?

Isn't that just the dark side of "Chromatic Aberration"

Since the light from certain colors shift wouldn't that make a discolored lighter and darker edge of bright objects?

I think you should compare the exact same scene using the exact same lens on 2 different camera models with their settings matching a closely as possible to identify the real cause for the black areas.

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Don

Marcel Knaapen Regular Member • Posts: 258
Re: Extreme pixel peeping

I think this is a result of sharpening.

OP bg2b Contributing Member • Posts: 897
Re: Chromatic Aberration?

I doubt it's chromatic aberration since it seems to be mostly on the right side (on horizontal pictures), and it doesn't seem to depend on the position of the highlight in the frame.

OP bg2b Contributing Member • Posts: 897
Re: Extreme pixel peeping

I don't think so. One of the worst examples is the photo that I cropped the top left example from. The photographer who took that photo wrote that aside from adjusting the white balance while developing in ACR, he used no noise reduction, curves adjustment, or sharpening.

Joo Veteran Member • Posts: 4,111
Re: Can you see it at 100%

I tend to view photos on the computer at 50% instead of at 100%. I find this to be a bit more realistic. Especially considering the bayer pattern.

So I think the better question would be if you can see them at 50%.

I saw odd behavior with the Canon EOS 10D but it never stopped me from taking decent photos. I wouldn't fixate on it too much at the moment.

Joo

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Dominique Dierick Veteran Member • Posts: 4,495
Canon disease ;)

1DmkII has it too. Did not notice it on 5D nor 20D.

D.

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Victor Engel Forum Pro • Posts: 19,387
Always on right?

Looks like the artifact is always on the right side, judging by your samples.
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OP bg2b Contributing Member • Posts: 897
Re: Always on right?

Yes, in horizontal shots, it seems to be almost always on the right.

Victor Engel Forum Pro • Posts: 19,387
Re: Always on right?

Maybe the ADC gets temporarily blinded by the saturated signal. I'd be curious to see what the raw data looks like. Got any raw files showing this artifact?
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OP bg2b Contributing Member • Posts: 897
Re: Always on right?

No, I've only looked at JPEGs (via camera, DPP, and ACR) that others have posted.

jsmiller Contributing Member • Posts: 826
It is correlated with severe overexposure.

Just looking at the images on screen it is clear that only the most heavily exposed parts of the image show this effect. Not having access to the original raw signal levels that were in each pixel makes it hard to diagnose the situation (we operate a detector lab where we manufacture and test CCDs and other detectors and do look at these kinds of data). I suspect it has nothing to do with noise reduction or sharpening. A wild guess is that to the left of the dark spots the pixels were either saturated (reached maximum counts) or had extremely high counts and this somehow affected the electronics of the readout, perhaps how the amplifiers or how ADC behaved. There is some kind of dead-time or recovery issue.

In actual use this will only be a problem when overexposure like this happens, as I didn't see any artifacts when it didn't happen, that is, overexposure below the threshold needed to produce the black spots. Of course, images with bright lights in them like these are just the ones that could give problems if one cares about the black spots, and I'm sure some will find them troublesome.

Joe

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(unknown member) Contributing Member • Posts: 873
looks like a hardware issue

the extreme overexposed pixels do not hold charge (charge is tunneling out) and reset to zero

Has anyone else seen this problem?

bg2b wrote:

Has anyone noticed the black dots that sometimes appear to the side
of extreme highlights in 5dii pictures? I saw this mentioned in a
thread on photo.net
( http://photo.net/canon-eos-digital-camera-forum/00RewZ ;), but I'm
finding it in some of the samples here too.

It seems to happen on shots processed with DPP and ACR, and in camera
JPEGs, so I don't think it's any sort of artifact from one converter.
It appears more prevalent at higher ISOs, but even at ISO 100 or 200,
you can sometimes find it.

I collected together some crops from various samples that I've seen
posted here and elsewhere. I believe this sample includes photos
from five different cameras, and the crops are all shown at 200%. I
apologize for the extreme level of pixel peeping, but when thinking
about shelling out that much for a camera, not to mention lenses, I
want to at least know more about it. In particular, how universal is
it, and if it's not just a case of a few bad cameras, is it fixable
in firmware or software?

-- hide signature --

Richard, NC
Never comment on something you don't know about

(unknown member) Contributing Member • Posts: 873
no-CA is not black

stewartde wrote:

Isn't that just the dark side of "Chromatic Aberration"

Since the light from certain colors shift wouldn't that make a
discolored lighter and darker edge of bright objects?

I think you should compare the exact same scene using the exact same
lens on 2 different camera models with their settings matching a
closely as possible to identify the real cause for the black areas.

-- hide signature --

Richard, NC
Never comment on something you don't know about

jonte0 Contributing Member • Posts: 506
Re: Extreme pixel peeping

It's the new contrast enhancer
Canon can!

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Fovea Contributing Member • Posts: 779
Re: You can see it at 50%

Just tried, you can see it at 50%, which is a bit annoying...

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vin_ Regular Member • Posts: 228
Re: Extreme pixel peeping

Agree, its a result of over sharpening-IMO
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