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02-15-2010, 11:20 AM   #1
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Pentax k-7 low light banding - normal or worrying?

I've taken a few shots in low light, very underexposed and then simply used autotune in adobe lightroom.

Shot at ISO100. Afaik it's the latest firmware.
Sure, noise levels are as expected but this type of banding shows up on each low light photo I brighten up excessively (same spot).

Seems like sensor overheat to me, but is this normal or should I be worried?
I havent tried to take a photo using ISO3200 under same conditions to see if this banding is seen. But I see it on ISO100 and digitally brightened.

The banding is visible at same location on all photos which is taken underexposed and brightened with auto-tune in lightroom.

02-15-2010, 11:25 AM   #2
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Looks like my attachment got broken somehow.

Fixed.
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02-15-2010, 11:42 AM   #3
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This is A/D converter read noise and it's normal, except (for example) in the case of the latest Sony sensors with built-in A/D converter(s).
02-15-2010, 11:44 AM   #4
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QuoteOriginally posted by asdf Quote
This is A/D converter read noise and it's normal, except (for example) in the case of the latest Sony sensors with built-in A/D converter(s).
Ok, so the broad "purple":ish band is normal and nothing to worry about?

02-15-2010, 11:56 AM   #5
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Since I can't see it at a casual glance, could you be more specific about what I'm supposed to be looing for?

Shooting underexpsed at ISO 100 and then push processing is *exactly* like shooting higher ISO. No advantage whatsoever; indeed, if 100 is the native ISo of the sensor, that all it ever actually anyhow. So if you're thinking shooting underexposed at ISO 100 and then pushing is going to give you less noise than simply upping the ISo, that's just no so. In fact, the opposite is just as likely to be the case, as in some cases at least, the analog amplication done in the camera is going to be less problematic than the digital amplification you are doing.
02-15-2010, 12:12 PM   #6
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I've marked the approx area the banding is more evident (thicker) than across the rest of the picture in dark photos that have been digitally brightened.

It's a vertical field with the following width (marked in purple).
You can see it on the example photo above aswell.

I'll try taking some shots at ISO3200 and see if the banding is visible if left to the camera to do the ISO adjustments.
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02-15-2010, 12:15 PM   #7
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Banding is very normal when you underexpose an image and then try to bring the levels up in post production.
Exposure accuracy is very important if you want to maximize image quality and reduce artifacts such as banding.
02-15-2010, 12:34 PM   #8
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QuoteOriginally posted by Norman Quote
Ok, so the broad "purple":ish band is normal and nothing to worry about?
There is fixed pattern noise and...not-fixed pattern noise. Fixed pattern noise can be removed...

Noise, Dynamic Range and Bit Depth in Digital SLRs

If you mouse over the picture in section 3, you can see the fixed pattern noise removed, whereas the fluctuating pattern noise remains.

It's probably best to expose correctly and avoid high ISO.

02-15-2010, 12:37 PM   #9
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Of course I agree that it's best to do proper exposing, but this was just for testing. My biggest worry was just that the pattern was so wide at one point of the image where I've marked with pink. It looks like a pink field has appeared ontop of the normal noise (sort of).

It was such an odd wide area which was slightly more pink toned across that part of the image.

Maybe Im just picky?
02-15-2010, 12:45 PM   #10
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QuoteOriginally posted by Norman Quote
Of course I agree that it's best to do proper exposing, but this was just for testing. My biggest worry was just that the pattern was so wide at one point of the image where I've marked with pink. It looks like a pink field has appeared ontop of the normal noise (sort of).

It was such an odd wide area which was slightly more pink toned across that part of the image.

Maybe Im just picky?
In the fixed patter noise of the Canon 20D example in the link I provided, some of the "bands" are more prominent than others, as well.
02-15-2010, 02:27 PM   #11
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Tested now at ISO3200.
No banding issue, the noise is uniform and similar all across the shot.

Don't know what to make of that. :P
ISO100 and digitally enhanced = banding .
ISO3200 with/without digital enchancement = no banding, just normal ISO noise.
02-15-2010, 03:38 PM   #12
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QuoteOriginally posted by Wheatfield Quote
Banding is very normal when you underexpose an image and then try to bring the levels up in post production.
Exposure accuracy is very important if you want to maximize image quality and reduce artifacts such as banding.
it is normal in canon cameras i guess, but i have yet to see it in my photos. And i habitually under expose.
02-15-2010, 03:59 PM   #13
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QuoteOriginally posted by zxaar Quote
it is normal in canon cameras i guess, but i have yet to see it in my photos. And i habitually under expose.
Would be interesting to see a comparison where you take a shot which is similary dark as mine. Then bring the levels up till you see noise, and see if there is any banding.
ISO100 of course.


ISO100 is the only one I've seen the banding issue when I bring levels up a lot.
02-15-2010, 04:09 PM   #14
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QuoteOriginally posted by Norman Quote
Would be interesting to see a comparison where you take a shot which is similary dark as mine. Then bring the levels up till you see noise, and see if there is any banding.
ISO100 of course.


ISO100 is the only one I've seen the banding issue when I bring levels up a lot.
i will check as i get time. Or I have some low light photos i will find them and put them online for others to see. It is possible that i may miss something and others can point it out. (it has happened before).
02-15-2010, 04:18 PM   #15
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Norman, this banding is very similar to banding on my first K-7, indeed. I could see it on any picture taken at any ISO when I brightened them up. It was at same place on the picture as it's on yours. But, the problem with that particular camera was that after 10 or so shoots, banding was visible even without brightening images, problably the result of sensor heating. There were even green and purple lines showing of the edge of that banding strip, after that 10 or more shoots. I send camera to Pentax Service and it was replaced due the faulty sensor. On replacement camera, there is no such banding whatshoever, only normal "pattern" noise when I brigten images up for a considerable amount, as asdf writes in his post. That is normal. The first camera was obiviously faulty, as photos taken in "normal" conditions were ruined.

Does this banding show when you use Live View?
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