week one lecture notes

7/27/2019 Week one lecture notes

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ACM202

what is a digital photograph?

Session 1, 2013

Alison Bennett


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The dematerialisation of the photograph

for the first time in history

the image is a dynamic system.

- Rush, M 2005, New Media in Art, Thames & Hudson, London, UK, p. 181

The photograph is no longer a

physical object but a collection ofnumbers translated at recall


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WHAT IS A DIGITAL IMAGE?


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A digital image is

a grid of pixels

With the technology back then,you had very limited palette in

which you were able to draw a

character. If you look at the

original Mario face, you had just 7

pixels to draw his face. My goal

within that limited palette was to

create a character that was as

distinct as possible. Because of

that, he had some of his now-

distinct features such as his big

nose.

Read more: Exclusive Interview

With Nintendo GamingMastermind Shigeru Miyamoto -

Popular Mechanics 18 December

2009
http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387http://www.popularmechanics.com/technology/gadgets/video-games/4334387


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A digital photograph is a fine grid of pixels

giving the illusion of continuous tone

12x16 pixels 800x900 pixels

http://epicrapbattlesofhistory.wikia.com/wiki/File:ERB_Mario_Bros.png


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pixel is short of picture element


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A picture made of

elements is not a new

idea: eg Mosaic

Mosaic portrait of a lady, PompeiiMuseo di Capodimonte

7


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Computers are basically

binary switch machines:

on or off; 1 or 0A fax or a photocopy: black or white


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Bits & pieces

BIT is short for Binary Digit: 1 or 0 (On or Off)

Bit Depth refers to how much tonal range is

available for each pixel.

A 1-Bit image is just black and white, like a

photocopy no grey.


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8 bit RGB vs bitmap

8 bit RGB bitmap

10


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The challenge of digital photograhy

To create the illusion

of continuous tone

vs. posterisation


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The illusion of continuous tone

Graduated tonal range VS Posterisation


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Levels of tone


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Levels per bit

Bit Depth Colours Available: 1-bit: black and white / on or off / 1 or 0

2-bit: 4 levels of tone per channel

4-bit: 16 levels of tone per channel

8-bit: 256 levels of tone per channel 16-bit: 32,768 levels of tone per channel

24-bit: 16.7 million levels of tone per channel

Each step in bit depth doubles the number oflevels of tone available within that colourchannel.Eg. 7-Bit = 128 levels


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Remember our challenge: Continuous tone

Human perception

requires at least 200

levels, steps in tone, to

create the illusion of

continuous tone

Therefore 8bit is the

most efficient bit depth

7bit=128 levels;

8bit=256 levels


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8bit: 256 levels of tone

16

White: 255Black: 0


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Material to virtual

How do we get from

continuous tone, as weperceive it in the world,

to digital photographicrepresentation?


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What goes on inside the camera?


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The sensor

The sensor is either

a CCD charged

coupled device or

a CMOS'Complementary

Metal-Oxide

Semiconductor'.


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2009: Nobel

prize for Physics

In 1969 Willard S. Boyleand George E. Smithinvented the firstsuccessful imagingtechnology using a digitalsensor, a CCD (Charge-Coupled Device).

The CCD technology makes use of thephotoelectric effect, as theorized by AlbertEinstein and for which he was awarded the 1921years Nobel Prize. By this effect, light istransformed into electric signals. The challengewhen designing an image sensor was to gatherand read out the signals in a large number ofimage points, pixels, in a short time. The CCD isthe digital cameras electronic eye. Itrevolutionized photography, as light could nowbe captured electronically instead of on film. Thedigital form facilitates the processing and

distribution of these images.

http://nobelprize.org/nobel_prizes/physics/laureates/2009/info.pdf

http://www.npr.org/templates/story/story.php?storyId=113527362
http://nobelprize.org/nobel_prizes/physics/laureates/2009/info.pdfhttp://nobelprize.org/nobel_prizes/physics/laureates/2009/info.pdfhttp://nobelprize.org/nobel_prizes/physics/laureates/2009/info.pdfhttp://www.npr.org/templates/story/story.php?storyId=113527362http://www.npr.org/templates/story/story.php?storyId=113527362http://www.npr.org/templates/story/story.php?storyId=113527362http://www.npr.org/templates/story/story.php?storyId=113527362http://nobelprize.org/nobel_prizes/physics/laureates/2009/info.pdfhttp://nobelprize.org/nobel_prizes/physics/laureates/2009/info.pdf


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Sensor & the Bayer Array


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Online video: pixel colour
http://www.youtube.com/watch?v=2-stCNB8jT8


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The difference between what you see and

what the camera sees

How you see an image How your camera sees the image


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eye more sensitive to mid tones


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What is light?


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Mid tones within the green band


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Additive RGB colour mixing


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White is all colours combined


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Colour film was made up of 3 layers

recording a tonal image of that colour


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Digital colour works much the same way


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Photoshop channels of RBG:

B&W channels determine the intensity

of primary colour for that sub-pixel

Notice that

the channels

are B&W?


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Getting in close: sub pixels

Have you got up close to the bigscreen in Fed Square?

33

RBG Channels:


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RBG Channels:grey scale of colour intensity: 0-255

a filter of how much of that colour channel to let

through


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RGB Colour: note B&W filters in Channels256 levels of Red x 256 levels of Green x 256 Levels of Blue =

almost 17 million possible colours

RED

R: 255

G: 0B: 0

GREEN

R: 0

G: 255B: 0

BLUE

R: 0

G: 0B: 255

Magent

a

R: 255

G: 0

B: 255

Cyan

R: 0

G: 255

B: 255

Yellow

R: 255

B: 0

G: 255

Channels

like B&W

filters


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FYI:

Seth Lambert

RGB Numbers of a 2 DPI Self-Portrait2005

320 individual sets of numbers

indicating the Adobe Photoshop color

values of the pixels of a 2 DPI

photograph of myself. The number

sets are selections from screenshots of

the Photoshop file. The original pixel

grid that makes up the digital

photograph is maintained in my final

grid of numbers. 1 pixel number set is

equal to 1 inch.

http://www.sethlambert.net/failures7.

php
http://www.sethlambert.net/failures7.phphttp://www.sethlambert.net/failures7.phphttp://www.sethlambert.net/failures7.phphttp://www.sethlambert.net/failures7.php

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