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02-18-2012, 08:33 PM   #1
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Noise in low ISO

Hi all,
I recently got this K-5 camera, and it worked very well in high ISO. I took it out to shoot some city skyline at blue hour today. I set the ISO to 400 and compensation to -1. When I checked the photos at 100% crop on my computer, I noticed that the dark part of the sky is full of noise. FYI, this happens in both RAW and JPEG format.

Here's a sample at 100% crop which I got this afternoon.

I wonder if this is normal to have so much noise at 400 ISO or it's just my camera's problem. I'm not even sure this is noise or not.

Cheers,
Dyno

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02-18-2012, 09:19 PM   #2
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That looks normal to me- it's just because it wasn't that bright outside.

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02-18-2012, 10:37 PM   #3
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Noise comes from two situations. First is the signal to noise ratio. Signal is light, noise is what the sensor will give you when there is no signal, no light. Second happens with long exposures where individual sensors overheat and give you noise.

You have to give the sensor something to work with. If the aperture is small, either a slow lens or setting, and/or the shutter speed is very short, and there is little light to begin with, the noise overcomes the signal and you get something like what you show.

I had exactly the same question as you. I adjusted my technique (better to say learned the technique) of using shutter speed and aperture to maximize the amount of light hitting the sensor. The brighter it is, the more room you have to play with. In low light if I need to speed up the shutter to freeze movement, I take some ISO. If I want depth of field, I close the aperture and up the ISO. In low light you are working on the edge of the capabilities of the camera, everything you do will have a tradeoff. The K-5 moves the edge over, gives more room to work.

So in your example, nothing was moving. The shutter speed should be set as low as practical. Focus not an issue so open the aperture. With as much light as possible hitting the sensor, noise will be less. It is possible that even leaving the iso at 400, getting the exposure up ( the image is dark) that noise would be less of an issue.
02-19-2012, 06:32 PM   #4
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Thank you guys for your advice.
I took one another photo in the day time. Perfect sunny day and ISO 100.
Is there anything I can do to avoid noise, besides photoshop?

100% crop

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02-19-2012, 06:33 PM   #5
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What noise?
02-19-2012, 07:09 PM   #6
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Looks pretty normal, if not happy then there is sotfware like Topaz DeNoise - Remove Noise, Recover Detail
Highly effective in dealing with noise.

Best of luck.
02-19-2012, 07:09 PM   #7
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I think your expectations are a bit high to be honest. Pixel peeping is ok to an extent, checking focus/sharpness, but there's nothing wrong with what you linked, especially that second one.

Unless you're doin massive prints, or displaying these on a huge monitor, I wouldn't worry about it.
02-19-2012, 08:53 PM   #8
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JPG'ing an image for display can also degrade an image, causing posterization, artefacts and 'blockiness'.

You are also aware that a sensor is like a big matrix of rectangular pixels. The closer you zoom, the easier it will be to identify the individual pixels

Anyway, I suggest printing out the images in question at any size less than A2, and see if you notice any problems looking at them from 30cm or further away. That's the real test.

02-20-2012, 02:04 AM - 1 Like   #9
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QuoteOriginally posted by Tom Woj Quote
............ Pixel peeping is ok to an extent, checking focus/sharpness, but there's nothing wrong with what you linked, especially that second one.

........., I wouldn't worry about it.
+1 on that!

Remember that your sensor is like a kind of array of tiny buckets capturing rain drops (: photons).

If the shower is scattered, (your light is low) nearby buckets may collect relatively very different amounts of drops. Your signal-to-noise ratio will be low.

If the shower is strong, (your light is bright) nearby buckets will collect relatively very near the same amounts of drops. Your signal-to-noise ratio will be high.

This is a fundamental law of nature - and your pictures illustrate just that!
02-20-2012, 07:17 AM   #10
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QuoteOriginally posted by Stone G. Quote
+1 on that!

Remember that your sensor is like a kind of array of tiny buckets capturing rain drops (: photons).

If the shower is scattered, (your light is low) nearby buckets may collect relatively very different amounts of drops. Your signal-to-noise ratio will be low.

If the shower is strong, (your light is bright) nearby buckets will collect relatively very near the same amounts of drops. Your signal-to-noise ratio will be high.

This is a fundamental law of nature - and your pictures illustrate just that!
Being an retired engineer, and previously a professional photographer, I always try to explain noise in technical ways. However, your explanation is perfect and accurate, and easy to understand. Thanks, and I hope you do not mind if I use it from now on, but I will not take credit for the explanation though.
02-20-2012, 07:29 AM   #11
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QuoteOriginally posted by dyno Quote
I wonder if this is normal to have so much noise at 400 ISO or it's just my camera's problem. I'm not even sure this is noise or not.
The first things I'd look at is whether or not the images are properly exposed. Because it will be huge factor in noise performance.

Having said that, I know the blue channel(ie. sky) is notorious for noise and so I think it helps to be aware of that.

And finally, on the issue of what you can do other than Photoshop, I'd highly recommend shooting in RAW and using one of the advanced RAW developer softwares out there such as; Raw Therapee, which has very good Noise Reduction capabilities and is completely free. However, if you can afford it, I would highly recommend looking at Lightroom or Photoshop as they both offer exquisite Noise Reduction processing(usually fully automated) and are imo. worth every penny.

Hope this helps.

PS. Don't underestimate the value of monochromatic noise(grain) in images.
02-20-2012, 07:29 AM   #12
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QuoteOriginally posted by dyno Quote
Thank you guys for your advice.
I took one another photo in the day time. Perfect sunny day and ISO 100.
Is there anything I can do to avoid noise, besides photoshop?

100% crop
I can see a good number of JPEG artifacts here, and these can make a photo look noisy. The only way to really test noise is to shoot in RAW, and make sure that sharpening is set to zero when you look at the photo, whether you use ACR, Lightroom, or the bundled software to view/edit the file.

Last edited by Designosophy; 02-20-2012 at 07:31 AM. Reason: spontaneously posted while I was in the middle of typing.
02-20-2012, 09:16 AM   #13
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CCD sensors often does better here, i already explained why in another thread.
When i'm home will look for an image to upload.
02-20-2012, 12:08 PM   #14
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QuoteOriginally posted by Anvh Quote
CCD sensors often does better here, i already explained why in another thread.
When i'm home will look for an image to upload.
False.
Look at Stone G.'s answer to understand why.
02-20-2012, 12:52 PM   #15
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What are you viewing your images with? The problem may be exacerbated.

What does the histogram look like for this image? Are you exposed properly?
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