BAS PHOTOGRAPHY WORKSHOP – THE SCIENCE OF SEEING (THROUGH THE CAMERA)

2nd May 2015, Partha Ray

AGENDA Our Eyes vs the Camera Variable aperture vs fixed aperture Sensor – The soul of the camera Sensor as Electron Bucket Bucket filling by adjusting time and water flow Color Blind Sensor with colored sun glasses Sensor size example of some modern camera – different sensor sizes If Sensor is a field, the sensels / pixels are bucket collecting rain water (photon rain) Filling buckets (with electrons) ~ charging a batteries, ISO Exposure – a function of overcharged, under charged and optimally charged batteries Bucket sizes in Professional, semi professional and amateur cameras Interplay of Aperture, Shutter Speed and ISO Nature’s gift – Shot Noise and who handles better Pitfalls of high ISO – which type of camera is more susceptible One-upmanship between sensor and ADC Q&A – too tired, prepared this between 9PM to 7 AM(today)

TAKE AWAYCamera has same type of components as in our visual system. The ADC (Analog to Digital Converter) is an extra which does not have biological equivalent (we are analog).The still camera has shutter (our eyes are video camera) which is also an extra. In our retina, we have cone cell to sense light intensity and rod cells to sense colors (most sensitive to Green, Red and Blue). Camera sensor is “color blind”. They have colored glasses on top to see color. There are double the number of Green glasses compared to blue or red. Why ? (clue – we were monkeys). Note that nature “des not have color”. It is a simulation of human brain. (Big topic, not part of this course). As human brain is million times more powerful that any image processing chip, professionals always process image outside camera using tools such as “Light room” and their brain /imagination. (separate topic, not part of this workshop).

Aperture control ~ Iris Shutter Sensor ~ Retina

Wire ~ NervesImage Processor ~ Brain

Lens ~ Lens

ADC

TAKE AWAYVARIABLE VS FIXED APERTURE – DYNAMIC RANGE 1. Our eyes are variable aperture

scanner. 2. Hence, we can see very dark to

very bright – nearly 24 stops (224).

3. The camera has fixed aperture. The best camera can only have a maximum dynamic range (darkest to brightest) of only 14 stops (limited by ADC, explained later).

4. The sensel (bucket) size and quality, the ADC determines the dynamic range (explained later).

5. The picture is build in our brain: we see through our brain, not our eyes.

Variable

Fixed

TAKE AWAYSENSOR, SENSELS OR PIXELS The sensors consist of many sensing cells and they are known as sensels or pixels. Modern cameras have between 16 to 24 Million sensels (with a few high mega pixel exception). These sensels collect photons or light particles and store them as electrons. This is very similar to collecting rain in millions of buckets which are stacked side by side in a field.However, in this case the rain can be started and stopped by a curtain which is called a shutter. Filling these buckets optimally is the key to proper photography. 36 mm

24 mm

The Sensor – Soul of the camera

Photons / Light particles

Sensels/ Pixels

The Sensor

TAKE AWAYFILLING THE BUCKET: HOW LONG X HOW BIG Exposure is all about filling the buckets to the max (when possible). If the water pressure is high (strong light), we can either use smaller opening (aperture) or shorter duration (higher shutter speed). Ideally, a dry bucket (dark, shutter closed, no exposure) should have no water (electrons). There is no ideal bucket (sensels) and real buckets always have some dirty water (stray electrons) sticking around. These are called dark noise (sensor noise).

How big? t = 1/60 second

How long?

Ideal darkbucket

Actual darkbucket

Electrons

Fully Exposed

Minimally Exposed

TAKE AWAYMAKING COLOR BLIND BUCKETS TO SEE COLOR The sensels are color blind – they just store electrons.

Therefore each pixel is covered by a colored glass or filter. This allows specific pixel or bucket to count photons / electrons of a specific color. These filters are of primary colors – R, G, B. There are 2x Green for each Red and Blue. Why?

TAKE AWAYTHE SOUL OF THE CAMERA The sensor is the soul of the camera. Professional cameras have bigger sensors. The biggest sensor size is 36 x 24 mm (35 mm format camera). This is same size as 35mm film. The sensors consist of many sensing cells and they are known as sensels or pixels. Modern cameras have between 16 to 24 Million sensels (with a few high mega pixel exception). Higher the pixel count, lower the pixel or bucket size. The sensor is like a football field that has got millions of buckets (sensels) for collecting rain water (photons – electrons).

The bucket / Sensel / Pixel

The colored glasses or filters

The football field or Sensor – Soul of the camera

Type 1/2.33" / Q M 4/3s APS-C APS-H 35mm Full frameSensor w x h 6.16 x 4.6 mm 17.8 x 10 mm 22.2 x 14.8 mm 28.7 x 19 mm 36 x 24 mmSensor area 28 mm2 178 mm2 329 mm2 548 mm2 864 mm2

crop factor 5.84 2 1.6 1.26 1

Pentax Q System Olympus OM-D E-M1 Canon 7D II Canon 1D IV Canon 5D IIIPanasonic Lumix Panasonic Lumix DMC Nikon D7200 Nikon D750Canon Powershot Sony a77 II Sony a99

~ body cost U$ 200 - 500 U$ 1000 U$ 1000 - 1500 U$ 2500

discontinued(~ U$ 5000)

Camera Models

TAKE AWAYHIGHER THE NUMBER OF PIXEL, LOWER THE PIXEL SIZE AND VICE VERSA. Even with in the same sensor size (e.g. full frame 36 x 24 mm or APS-C 22.2 x 14.8 mm), the number and size of buckets / sensels / pixels vary. Within a same sensor size, if the pixel count goes up, the pixel size has to come down. The combination of bucket size and numbers (mega pixels) results in different capabilities (explained later).

36 mm

24 mm

15 mm22 mm

3.42 mm4.54 mm

Smaller Field – APS-C

Big field with big buckets – Full frame with relatively low mega pixel

Big field with many small buckets – Full frame with relatively high mega pixel

TAKE AWAYFilling Buckets ~ Charging Battery When buckets or sensels are full of electrons, it is a fully charged battery. Sensels recording brightest part of the photo is fully charged. When buckets or sensels have just a few electron, it appears as a discharged or empty battery. Sensels recording darkest part of the photo is charged at its minimum. In a properly exposed photo, most of the sensels are properly filled or charged. In a poorly exposed photo, most of the sensels are not properly filled or charged. In low light situations, when pixels or batteries cannot be charged optimally, a voltage multiplier (amplifier) is applied. It is very similar to increasing volume of your music system. This amplification gain is referred as ISO (increase). The ISO definition came from chemical film (1934) and has no direct meaning in Digital Camera. Higher ISO simply means higher gain of the amplifier.

- e 010

20 3040

50 xNN = 1

(i.e. ISO = 100)

Analogto

Digital

10110100110010

ImageProcessor

- e 010

20 3040

50 xNN = 8

(i.e. ISO = 800)

Analogto

Digital

10110100110010

ImageProcessor

ISO

TAKE AWAYOver exposure means that the buckets or sensels are over flowing (of electrons) – all white.

Under exposure means that the buckets or sensels have minimal or no electron.

In a optimally exposed photograph, the brightest area of the photograph fills the bucket of sensel to brink without overflowing while the darkest area has some minimum electrons to dominate over the stray electrons (enough clean water to dilute the dirty water).

TAKE AWAY1. Full frame camera has very high

Signal to noise ratio. They are also the costliest cameras.

2. Camera with smallest sensors have lowest SNR. They are also the cheapest .

3. Newer cameras have better SNR. 4. Some cameras have very large

bucket, relatively lower SNR but still very costly (e.g. D4s, U$ 6000)

5. What is the advantage of bigger buckets or sensels?

6. A new trend: Cameras such as the Leica X2,Fuji X100S, Nikon COOLPIX A, feature an APS-C sensor (23.7 x 15.6 mm) along with a fixed-focal-length lens.

Sony RX1which does the same, but with a Full Frame sensor (36 x 24 mm). These are ultra high end compact cameras.

Make Model Date Y Pixels Y Pixels X Mega Size Y Size X Pixel Size Bits ISO series 2Pixel ISO Read Noise Sat Cap SNR QE

Nikon D3s 2009 2844 4288 11.63 24 36 8.4 14 100 26.0 84,203.4 3,243.5 58%Nikon D600 2012 4028 6080 23.36 24 35.9 5.9 14 100 7.4 76,443.6 10,334.2 54%Nikon D800 2012 4924 7424 34.86 24 35.9 4.7 14 100 4.6 48,818.0 10,724.0 51%Nikon D800E 2012 4924 7424 34.86 24 35.9 4.8 14 100 5.2 54,923.9 10,636.8 54%Nikon D4 2012 3292 4992 15.67 23.9 36 7.2 14 100 18.8 118,339.0 6,284.8 53%Nikon Df 2013 3292 4992 15.67 23.9 36 7.2 14 100 21.7 134,567.1 6,208.3 60%Nikon D610 2013 4028 6080 23.36 24 35.9 5.9 14 100 5.7 74,971.2 13,116.3 50%Nikon D810 2014 4928 7380 34.68 24 35.9 4.9 14 100 4.5 49,553.7 11,012.9 48%Nikon D750 2014 4032 6032 23.19 24 35.9 6 14 100 5.5 81,607.7 14,851.3 52%Nikon D4s 2014 3288 4936 15.48 23.9 36 7.3 14 100 14.0 125,596.7 8,973.6 55%

Make Model Date Y Pixels Y Pixels X Mega Size Y Size X Pixel Size Bits ISO series 2Pixel ISO Read Noise Sat Cap SNR QE

Nikon D3000 2009 2868 4310 11.79 15.8 23.6 5.5 12 100 14.6 29,246.4 1,998.4 29%Nikon D5000 2009 2868 4310 11.79 15.8 23.6 5.5 12 100 5.6 28,283.6 5,076.9 35%Nikon D300s 2009 2868 4352 11.90 15.8 23.6 5.4 14 100 6.5 26,154.2 3,993.1 32%Nikon D3100 2010 3084 4672 13.74 15.4 23.1 4.9 14 100 15.7 29,504.7 1,877.2 34%Nikon D7000 2010 3280 4991 15.61 15.6 23.6 4.7 14 100 3.1 38,317.8 12,233.0 45%Nikon D5100 2011 3280 4992 15.62 15.6 23.6 4.7 14 100 4.1 39,022.4 9,537.9 46%Nikon D3200 2012 4012 6080 23.26 15.4 23.2 3.8 12 100 4.7 28,773.8 6,102.4 44%Nikon D5200 2012 4020 6036 23.14 15.7 23.6 3.9 14 100 2.7 27,429.1 10,295.6 39%Nikon D5300 2013 4016 6016 23.04 15.6 23.5 3.9 14 100 3.4 33,924.7 9,869.6 54%Nikon D7100 2013 4020 6036 23.14 15.6 23.5 3.9 14 100 3.3 29,441.6 9,000.9 42%Nikon Coolpix-A 2013 3280 4992 15.62 15.6 23.6 4.7 14 100 3.6 40,408.4 11,220.7 46%Nikon D3300 2014 4016 6016 23.04 15.4 23.2 3.9 12 100 8.5 35,988.8 4,246.1 58%

Make Model Date Y Pixels Y Pixels X Mega Size Y Size X Pixel Size Bits ISO series 2Pixel ISO Read Noise Sat Cap SNR QE

Nikon Coolpix-P70002010 2742 3664 9.58 5.7 7.6 2.1 14 100 4.4 7,535.6 1,723.5 51%Nikon 1-V1 2011 2606 3904 9.70 8.8 13.2 3.4 12 100 12.5 22,826.6 1,825.3 45%Nikon Coolpix-P71002011 2744 3664 9.59 5.7 7.6 2.1 12 100 4.5 7,271.0 1,613.4 56%Nikon 1-J1 2011 2606 3904 9.70 8.8 13.2 3.4 12 100 12.2 23,681.0 1,933.7 47%Nikon 1-J2 2012 2604 3904 9.70 8.8 13.2 3.4 12 100 14.7 24,808.0 1,686.1 46%Nikon Coolpix-P77002012 3024 4032 11.63 5.6 7.4 1.8 12 100 3.4 8,781.9 2,608.7 73%Nikon 1-V2 2012 3082 4620 13.58 8.8 13.2 2.9 12 160 7.9 11,602.7 1,466.3 53%Nikon Coolpix-P3302013 3024 4032 11.63 5.6 7.4 1.8 12 100 3.4 8,367.8 2,440.4 82%Nikon 1-AW1 2013 3082 4620 13.58 8.8 13.2 2.9 12 160 7.2 10,712.0 1,497.2 52%Nikon 2013 3024 4032 11.63 5.6 7.4 1.8 12 100 2.9 8,658.4 2,940.7 72%Nikon 1-S1 2013 2602 3948 9.80 8.8 13.2 3.3 12 100 11.1 21,748.1 1,952.0 49%Nikon 1-J3 2013 3082 4620 13.58 8.8 13.2 2.9 12 160 7.0 11,775.8 1,671.7 52%Nikon 1-V3 2014 3502 5248 17.53 8.8 13.2 2.5 12 160 11.8 13,636.4 1,156.9 63%Nikon 1-J4 2014 3502 5248 17.53 8.8 13.2 2.5 12 160 11.5 13,266.6 1,154.5 62%

TAKE AWAY1. A major differentiator

between higher end and lower end camera.

4.7µm4.7µm= 22.09µm2 (e.g. D800)

Pixel Size / Pixel pitch

TAKE AWAY

All Camera settings or modes (auto, manual, aperture priority, shutter priority, etc.) plays around with these three basic settings. Auto: Camera decides al three. Manual: Photographer decides all three. Aperture Priority (A, Av): Photographer decides aperture, camera decides the rest two. Shutter Priority (S, Tv): Photographer decides shutter speed or time value, camera decides the rest two.

XTime value / Shutter speed

Aperture size or f stop number

XISO or gain

1) Moving object? Need higher shutter

speed.

2) Open up aperture to fill the buckets?

3) Buckets still not full? Increase ISO. 1) Doing landscape,

need higher DOF, smaller aperture

2) Reduce shutter speed to fill up the sensels / exposure.

3) Low sun light, insufficient

exposure, increase ISO.

TAKE AWAYSHOT NOISE, PHOTON NOISEEven under uniform illumination, there is small variation of light or photons reaching each pixel or bucket. This variation manifest as grains in the photograph. This is called shot noise. It is measured as,

Small variation in level

With smaller bucket, the variations are more pronounced.

√ √125,597

125,597=354.4

√ √81,608

81,608=285

D4S

D750

Bigger Bucket win in handling Shot Noise, useful in low light photography

(Poisson Noise)

TAKE AWAYSENSOR NOISE There are noise (stray electrons) in any sensel. They get amplified at higher ISO. The noise also increases with temperature / long exposure (thermal noise). Hence keep your camera cool. Modern high end camera (high SNR), this problem is now minimal. They can operate at high ISO.

Semi-professional and in compact camera, this problem is profound as they tend to use smaller sensels. Shot noise is any way relates to “well” bucket capacity. Thus, any smaller sensel camera is susceptible to shot noise.

For example, latest full frame high mega-pixel cameras – Canon 5DS (50MP), Nikon D810E (36MP) cannot operate at higher ISO. These cameras are targeted for high resolution landscape photography (note that the lens should also be capable of resolving higher resolutions).

Minimally Exposed = X =

The Stray also get multiplied

TAKE AWAYWHEN SENSOR KNOCKS THE ADC’S DOOR.

• 12 bit ADC (earlier)• Improving Sensor

• 14 Bit ADC (now)

010

20 3040

50 xNAnalog

toDigital

10110100110010

ImageProcessor

Ideal sensel, Zero sensor Noise. Well capacity 100,000. Hence the dynamic range is 100,000 as far as the sensor is concerned.

However, the ADC is 14 bit. It means it can count from 0 to 214, which is 16.384.

Hence, this is the limit to dynamic range even if the sensor is ideal.

Hence, with improving sensor, we will see >14 bit ADC.

Keep all your questions for the other three.