Computer Science E-7Exposing Digital Photography

Lecture 6: The HistogramOctober 19, 2009

danallan@mit.edu

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Histograms General Histogram

Image from http://en.wikipedia.org/wiki/Histogram

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Histograms Digital Photography

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Black WhiteSome

Many

Histograms Total Underexposure

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Histograms Total Overexposure

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Histograms Well-exposed samples

Photo by Dan Armendariz, 2009309s, ISO 100

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Histograms Well-exposed samples

Photo by Dan Armendariz, 20071/1000s, ISO 400, f/5.6

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Histograms Well-exposed samples

Photo by Dan Armendariz, 2007

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Histograms

Under-exposure

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Photo by Dan Armendariz, 2005

8.0s, ISO 100, f/8

Histograms

Over-exposure

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Photo by Dan Armendariz, 2005

15.0s, ISO 100, f/16

Histograms Exposure Compensation

Photos by Dan Armendariz, 2005Left: 1/80s, ISO 400, f/2.8, 0ev. Right: 1/80s, ISO 800, f/2.5, +1.3ev

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Histograms Over- & Under-exposure

Photo by Dan Armendariz, 20061/80s, ISO 400, f/10

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Bits and Bytes Refresher

Bit 0 or 1

Byte 8 bits

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Bits and Bytes As related to histograms

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Black White0 255

Bits and Bytes Bit Depth

JPEG

Red Green Blue

8-bit 8-bit 8-bit

0 255 0 255 0 255

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Histograms What about color?

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Red Green Blue

?

The Eye Luminance Detection

Image from http://en.wikipedia.org/wiki/Trichromacy

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The Eye Luminance Detection

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Red Green Blue

Luminance Calculation

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Luminance ≈ 0.3 R + 0.59 G + 0.11 B

Luminosity Histograms DIY!

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Luminosity Histograms DIY!

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Luminosity Histograms DIY!

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Histograms More than just Luminosity...

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Lum

R

B

G

Histograms Luminosity, Colors, & RGB

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Lum

Colors

RGB

Histograms Luminosity, Colors, & RGB

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Images from http://www.cambridgeincolour.com/tutorials/histograms2.htm

Histograms Luminosity, Colors, & RGB

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Images from http://www.cambridgeincolour.com/tutorials/histograms2.htm

Histograms What is Black and White?

Photo by Dan Armendariz, 20061/80s, ISO 400, f/10

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Dynamic Range The Eye

Image from http://en.wikipedia.org/wiki/Fovea

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Dynamic Range Digital Cameras

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Pixel (“Bucket”)

Photons (Light)

Collected Light

Dynamic Range Simplified Calculation

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Dynamic Range =Biggest Signal (full “bucket”)Smallest detectable signal

Dynamic Range In Scenes

Photo by Dan Armendariz, 20061/80s, ISO 400, f/10

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Computer Science E-7Exposing Digital Photography

Lecture 6: The HistogramOctober 19, 2009

danallan@mit.edu

32