Noise

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iainpeden
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Noise

Post by iainpeden »

A comment on another thread prompts me to ask the question " What is meant by noise in a digital photo?"
(Mark Twain: There are lies, there are damn lies and then there are statistics)

Timc
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Re: Noise

Post by Timc »

I suppose the most accepted (simplified) definition is, and I quote:

"In digital photographs, “noise” is the commonly-used term to describe visual distortion. It looks similar to grain found in film photographs, but can also look like splotches of discoloration when it’s really bad, and can ruin a photograph. Noise tends get worse when you’re shooting in low light."

However, in most circumstances I'd rather view an image with "noise" over an over-sharpened image and all that goes with it, others will probably disagree! :smile:

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Harvo266
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Re: Noise

Post by Harvo266 »

As above:
In simple terms its when you can see grain in the photo. The usual causes is over cropping, under exposed photos and/or high ISO. If you have a camera, just try taking a photo with the ISO as low as possible and then take the same with the ISO as high as possible with the settings adjusted accordingly. You'll notice the difference
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boff180
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Re: Noise

Post by boff180 »

Good example of what noise is - is to use this tool from DPReview....

https://www.dpreview.com/reviews/image-comparison/fullscreen?attr18=daylight&attr13_0=pentax_kp&attr13_1=pentax_k3ii&attr13_2=nikon_d7100&attr13_3=nikon_d7100&attr15_0=jpeg&attr15_1=jpeg&attr15_2=jpeg&attr15_3=jpeg&attr16_0=100&attr16_1=100&attr16_2=100&attr16_3=1600&attr126_0=normal&attr126_1=normal&attr126_2=normal&attr126_3=normal&attr171_0=off&attr171_1=off&attr171_2=off&attr171_3=off&normalization=full&widget=490&x=0&y=0

Select the same camera on two image windows and set both to JPEG.... select two vastly different ISO's say.... ISO100 and ISO1600 and compare. You will see the nose in the ISO1600 image.

Sky, particularly blue, is a sod for showing up the slightest noise.

Adobe Lightroom Noise Reduction in the Develop module is quite effective at getting rid of it however I own a copy of Topaz Labs' DeNoise 6 which acts as a filter in Photoshop or as a Standalone piece of software - it is superb.

Andy

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AlexC
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Re: Noise

Post by AlexC »

boff180 wrote:Sky, particularly blue, is a sod for showing up the slightest noise. Andy


Which is obviously particularly inconvenient for us. :sad:
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ted633
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Re: Noise

Post by ted633 »

AlexC wrote:
boff180 wrote:Sky, particularly blue, is a sod for showing up the slightest noise. Andy


Which is obviously particularly inconvenient for us. :sad:


Not in the UK it isn't!

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speedbird2639
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Re: Noise

Post by speedbird2639 »

Not in the UK it isn't!


No - but the fact the air forces have started painting all their aircraft the exact same colour as a British overcast means on some photos you take the only indication the camera was pointed at an aircraft is the pilot's canopy and the squadron markings visible in the final photo!

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wallace
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Re: Noise

Post by wallace »

Most noise in digital photography either comes from bad sharpening, USM, a global sharpening makes trouble where there is none or pushing under exposures, expose to the right and hope for the best.... just like in the days of slide film :)

Alanko
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Re: Noise

Post by Alanko »

I'm not a big photography guy, so 'noise' for me is something I've encountered when pointing a smartphone at something and discovering an endlessly changing speckled texture in dark areas of the photograph. For example you photograph your mates in a dingy bar. They are illuminated pretty well by single the overhead light, and the fruit machine in the background looks alright, but the dark wall to the right of it just isn't reproduced very well. The camera has gone to town adding data, as though it isn't very happy with the absence of content in that area of the photo. This was a particular issue when smartphone makers started trying to up the megapixel count without making bigger sensors.

Perhaps I'm not explaining this very well, but the academic definition of noise has already been covered well in this thread. I went digging through my photographs for a real-world example, and it didn't take me too long to find some noise:

Image

This is a cropped area of a much bigger image I captured with my Canon EOS 500D. What you are seeing here is Broughton High School and lights along East Fettes Avenue, taken in twilight conditions. The Canon has introduced areas of faint green and red speckling with the occasional markedly darker or lighter pixel. It isn't a true reproduction of what was actually there on the evening.

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