Photonrate

Time

End of exposure End of exposure

IdealRate of incoming light is constant

RealityRate of incoming light is fluctuating

Photonrate

Time

How much fluctuation?

√nDictated by Poisson (pwasõ) Distribution

For n total photons in exposure,

standard deviation =

Photons collected = n + √n

If n = 10,000 photons,Photons collected = 10,000 + √10,000 = 10,000 + 100 photons

10,000 photon

s

9,900photon

s

10,100photon

s

9,950photon

s

√n, so what?Variable brightness = noise!

Noise monsterOne of the photographer’s worst enemies

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000%

2%

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12%Proportion of fluctuation

sqrt(n)/n

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(√(n

)/n)

Photons

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1%

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8%

Canon A570ISCanon A570IS

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Photons

Canon A570IS7.1 Megapixels1/2.5” sensor5.76 x 4.29mm (24.7mm2)Density: 3.48 μm2/pixel

0 500 1000 1500 2000 2500 3000 35000%

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Canon 5DNikon D300Sony H9

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90 900 90000%

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Canon 5DNikon D300Sony H9

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Photons

ISO100 ISO200 ISO400

ISO800 ISO1600

Canon A570IS7.1 Megapixels1/2.5” sensor5.74 x 4.3mm (24.7mm2)Area: 3.48 μm2/pixel

0 500 1000 1500 2000 2500 3000 35000%1%2%3%4%5%6%7%8%

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images: dcresource.com

0 10002000300040005000600070008000-2%

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ISO800 ISO1600

Fuji F306.1 Megapixels1/1.7” sensor7.7 x 5.77mm (44.4mm2)Area: 7.27 μm2/pixel

100200400800

1600

images: dcresource.com

0 100002000030000400005000060000-2%

0%

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ISO100 ISO200 ISO400

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Canon 30D8.2 MegapixelsAPS-C sensor22.5 x 15mm (337.5mm2)Area: 41.16 μm2/pixel

1002004008001600

images: dcresource.com

30D

30D

F30

F30

A570IS

A570IS

8.2 Megapixels22.5 x 15mm (337.5mm2)Density: 41.16 μm2/pixel

6.1 Megapixels7.7 x 5.77mm (44.4mm2)Density: 7.27 μm2/pixel

7.1 Megapixels5.76 x 4.29mm (24.7mm2)Density: 3.48 μm2/pixel

ISO100 ISO200 ISO400 ISO800 ISO16000%

1%

2%

3%

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8%Canon A570IS

Fuji F30

Canon 30D

Canon 5D

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ISO

More photowells mean less photons per pixel

Making matters worse, circuitry must occupy some space between each photowell – the more photowells, the more space circuitry takes up.

SummaryMore pixels, smaller sensor => less light per pixel => more noiseLess pixels, bigger sensor => more light per pixels => less noise

In theory, the biggest sensor with the least pixels will give us the best image, in terms of noise.

A 1-pixel sensor would be ideal.

With 1 pixel, we’d have low noise but no detail.

Many pixels => High detail, high noiseFew pixels => Low detail, low noise

The “Megapixel Myth”: Detail vs. Noise

Megapixels: Detail vs. Noise

Facebook profile picture: 4x6 studio print at 300dpi:

5x7 studio print at 300dpiStandard VGA TV:

1080p HDTV: Projector Screen:

8.5x11in, 300dpi magazine spread:10x14in, 150dpi full-page spread in Daily Cal:

Giant 20x30in poster print at 150dpi:

0.03 MP2.16 MP3.15 MP0.35 MP2.07 MP1.92 MP8.42 MP3.15 MP13.5 MP

How many pixels do we need?:

If you only look at pictures on the computer, 2-3MPIf you make non-poster-size prints (4x6, 5x7, 8x10), 3-4MP

More pixels beyond this don’t add detail, but contribute to greater noise

Caveat: assuming same sensor technology

Chrominance NoiseVariation in color

Luminance NoiseVariation in brightness

Random NoiseFluctuation in light input (random distribution of photons)

Fixed Pattern Noise-Consistently reproducible noise-Caused by electronics, sensor defects, heat-Manifested as “hot pixels” or luminance anomalies-Since noise is reproducible (non-random), easily fixed by dark frame subtraction