Camera Labs

Many articles refer to the superior performance of large sensors in available light photography at high ISO. Due to their larger area that can capture the light they need less light for the same amount of signal/noise (s/n) ratio than smaller sensors as you find them in point&shoot cameras.

That is correct. But one should not underestimate the effect of better s/n ratios on pictures captured at “normal” ISO values like 100 (standard) or 200 (my default): If you shoot high contrast pics chances are that there are some areas that are not well lit and thus easily get 10 stops less light than the well lit parts of the scene. So the sensor gets 1/1000 of the light in these corners of your pic than in other corners.

From ISO 100 to ISO 800 (or ISO 200 to ISO 1600) is only a difference of 3 stops! What do you think will happen? Well, assuming an even distribution of brightness in you pic, 70% of your picture will have a s/n-ration that is as bad as or even worse than what you get when you crank up the ISO to 800 or 1600!
Even if you assume that the exposure is oriented at the median light values 5 stops below the highlights still 30% of the pic have s/n ratios like in high-ISO shots.

That casts some light on the frustration that some users of point&shoots have even at ISO 100 and also makes it clear that low noise is important even in bright daylight. And it also explains, why the point&shoots that I know tend to overexpose: The manufacturer likes to get enough light for the mid-tones that would otherwise suffer from bad noise even at ISO 100…

P.S.: I will scan my archive for an appropriate example that can demonstrate the above.

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

When the user selects a higher ISO, that means that the camera is using a faster shutter speed and then amplifying the signal more (thus increasing noise vs. the signal). But what you seem to be saying is that the dark areas of a photo have their own kind of default high ISO because there is less light to translate into the image -- thus, the S/N ratio is higher in the dark areas of a picture.

I've seen lots of sample photos on review sites that have noise in the shadows. With my Canon A620, the highlights are usually clean, and the dark areas are consistently dark, but I see a lot of noise in medium-dark to medium-bright areas of the photos. It's possible, of course, that there is noise in the dark areas but I can't see it. Noise in dark areas of a photo is usually chroma-type noise, and I don't see any of that in the photos I take with the A620 at the lowest ISO.

I have owned three cameras, all Canon A-series: A40, A95 and A620. Curiously, the A40 (2 MP) had less noise in its photos than either of the newer cameras, even at the lowest ISO. I'm glad to have the higher resolution in the A620, but it is disturbing to see so much more noise.

My next camera, I've decided, will be a DSLR. Despite it's lack of a power adapter, I will probably get the Olympus E-510. However, in Gordon's sample photos, the skies look very mottled -- and mottled skies means noise. It seems that in order to avoid noise, one has to get the most expensive pro DSLR with a very large sensor.

I definitely agree with you that noise is an important issue at low ISOs. I look at a lot of sample photos, and point-and-shoot cameras always show a lot of noise even at the lowest ISO. What really surprises me, however, is how often the reviewer calls the photo quality "good" or "excellent" despite the noise. But that's another issue ...

Hi Caleb,

I just wanted to point out, that there really is no difference in the effect of low light on the sensor - be it through higher ISO (and thus shorter shutter speed and/or smaller aperture) or through dark parts in your picture.
It's not that the camera cranks up the ISO/amplification in the dark parts, but the s/n-ration of the photo-cells in the dark parts is nonetheless worse than in the bright parts and you can definitely see more speckles and freckles in the dark parts.
That we don't see them so prominently just has to do with our eye (and our senses) beeing drawn to the brighter parts.

And yes, you're right: Sometimes the noise even becomes visible in medium-bright areas! This tends to be the case when these areas have little structure (like some out-of-focus background). In this cases the noise stucks out

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Yes, but cameras DO crank up the amplification when the ISO has been increased, right?

With my A620, I am finding noise along any edge in the photo. I took a lot of photos of houses with clapboards, and there was a lot of noise along all those edges of the clapboards. Is that actual noise, or is that the result of noise reduction?

By the way, I'm going to post a thread soon about Fuji cameras. They have been getting good reviews -- especially the cameras with "super-CCDs" -- but I find their pictures consistently noisy -- not from sensor noise, but from over-aggressive noise reduction. The noise-reduction that Fuji uses causes a poster- or paint-like effect. Judging from the reviews and forums, I seem to be the only one who thinks Fuji cameras aren't good.

Caleb

Yes, when you up the ISO, amplification goes up too. But that's not the reason for noise, at least not the noise from the sensor. That totally depends on the amount of light that hits the photo-cell. Amplification only makes the noise brighter, so to speak.
Todays point&shoots can be compared to a combination of a tape-deck and a hifi-amplifier: Even if you buy the best amp with world-class s/n-ratio, it will only amplify the noise of the tapedeck (beeing the equivalent of a small sensor).

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Good analogy Thomas. Garbage In, Garbage Out. You can't make a silk purse out of a sows ear.

BTW, "tape deck", how very 1985, lol.

Zorro.

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http://zorrofox4.deviantart.com/



Various lenses, SB800 & Manfrotto 190 with 460MG head

lemme get this straight.
increasing the ISO increases the gain of the sensor right? So for the same picture, at ISO 100 if i dont notice any freckles, but do notice freckles in the dark parts, that explains it.

But in the medium bright parts [ or out of focus backgrounds], the brighter parts get amplified but the dark parts remain dark. so the difference is amplified. Darkness cannot be amplified. Light can.

now to sensor area, a small sensor area captures less information. so the quantization noise should be higher. which shows up in the pictures with the PnS cams. kind of like spreading a constant amount of paint on one square cm vs one square inch. if you poke a pin, the smaller square has deeper paint. to make the paint constant, the larger square can take more paint. similarly the larger sensor can accept more light.

i generally use iso100. but occasionally have to go with 200 or 400. generally one bump on the ISO gives one bump down on the shutter delay keeping aperture constant.

well this what i understand. if there are errors, please do correct me.

thanks
ram

I don't believe that the cam applies variable (analog) amplification of the sensor in one shot on dark, medium and bright parts. I think all procrastination of contrast is done post shooting digitally. But then maybe I'm wrong.
The other question for me is: If the amount of light hitting the photocell is really very, very small, is the cell giving a "zero" without noise (what I would assume) or is there something that I would call "darkroom-noise" that could be amplified (I'm not talking about "hot pixels")?

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Well, here I'm back as promised with some example of ISO 200 noise in darker areas with my D80:
This is the full pic (just a little cropping applied)


And this is a 100% crop to show the noise on the out of focus background plants


It's not bad, but if you take a smaller sensor camera that noise would stand out quite prominently.

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Tom, I see that no one replied to your post -- I should have replied, sorry.

What I am finding is that all cameras -- even DSLRs -- have visible noise in the dark areas. So the noise that you show in that shot is not surprising. What that noise looks like to me is noise which has become somewhat mottled by noise reduction. I don't know why, but the noise reduction algorithms used in cameras seems to lead to certain effects: a paint-like or chalk-like effect or mottling. If that noise were unprocessed, I believe it would look finer, like grains of sand.

I haven't re-read this thread because I'm busy, so I'm not sure what we were talking about.

Film probably had lots of noise too, but no one noticed it because few people looked at their photos enlarged. It's only with digital that we can look at every pixel.

Caleb

Yep you're right. All dark areas even of the best DSLRs display some amount of noise.

Me, I'm pretty content with what the D80 delivers and I sometimes find the discussion about noise a little over the top.

As to your remark regarding denoising: I'm not sure whether this is the result of sharpening that you can see. I normally don't have noise reduction on, but I use normal ("auto") sharpening and the blots are less pronounced when I switch to "no sharpening".

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

Well then, perhaps you can answer some questions about the D80, which I'm considering.

Is it possible to turn noise reduction off altogether? And when the noise reduction is on, does it result in very soft images, or are they fairly sharp?

Thanks,

Caleb

The D80 has no in-camera menu for noise-reduction. You can only do it with post-processing. In CaptureNX there is a dialog where you can set the strenght of noise-reduction to 0-100%, the sharpnes to 0-10 the mehtod to "fast" or "high quality" adn there is an additional check-box for the reduction of "edge-noise" (not sure I got that right, it is a direct translation of the German menu).
With a strength of 7% and sharpening of "3" you get rid of the freckles in the shadows without killing the delicate hair-structure of the dog to much.

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Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews, My Pictures, My Photography Blog
D800+assorted lenses

I just looked up the specs of the D80. It does have "high ISO" noise reduction. That would seem to indicate that noise reduction isn't used at low ISOs, which means that the camera is doing very well in the noise department. Even the new Olympus cameras have visible noise at the lowest ISOs (when noise reduction is off).

Caleb

The D80 also has Long Exposure NR, whatever that is, lol.

Zorro.

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http://zorrofox4.deviantart.com/



Various lenses, SB800 & Manfrotto 190 with 460MG head