Transcript Slide 1

Digital Photography
Photo Organization
September 13
Checkpoint
• Signed Camera Check Out Form
• Brainstorm notes
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Week 2
Think about what types of images you may take
Think about when you may take them
Think about how you may edit them in class
Keep in mind that you may take several thousand photos this
semester, and may have several saved versions of each
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Organization
• Let’s discuss what we came up with
 We can always use somebody else’s ideas for
this, if we like it better than the way we did it!
• You guys have it much easier for
organization than past classes, because
Adobe CS2 offers a lot of cool stuff
 Note: only the black computers have CS2, not
the silver ones
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Adobe Bridge
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Adobe Bridge
• Views:
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Thumbnail
Filmstrip
Details
(Versions and alternates)
• For all these views, you can change size of
image displayed
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Metadata
File Properties
IPTC Core - Standard bunch of metadata for files
Camera Data
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Keywords
• Some pre-defined keywords, but the user
has complete freedom in choosing
Keyword Sets and
individual keywords
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Ranking
• Built-in easy way to rank images
• Select an image and the dots beneath the
image are selectable and change to stars,
based on your choices
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Other Features
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Rotation of images
Labeling
Filtering (based on rank or labels)
Find - can base it on several criteria
• And more!
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Lab Time
• You can begin to use Bridge
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To set up your organization structure
To rotate any images
To identify and delete any “out-takes”
To assign rankings, keywords, etc
• Have fun, but begin a solid structure that
you can build upon
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Homework
• Read Chapter 2
• We will discuss tomorrow & Thursday in
class
• It is difficult material!
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Light and Sensors
Lecture 04
September 14, 2005
Entering complex material…
MDP Chapter 2
Photography is about light
• Photography = “to write with light”
• So we have to understand a little about
light to understand how cameras work
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How we see light
• White Light (from the sun) is made up of colors,
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and each light has a certain wavelength
Light waves are either reflected, absorbed, or
transmitted – which is determined by the object
that the wave hits
and
 The color we QuickTime™
see is based on
theatype of light sent to
TIFF
(Uncompressed)
or red light
our
eyes
 An apple is reddecompress
because it reflects
are
needed
toblack,
see this
picture.
 For an
objects
to be
all wavelengths
of light are
absorbed, no light is reflected
• The primary colors of light are red, blue and
green (we will talk more about this later)
http://imagers.gsfc.nasa.gov/ems/visible.html
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How a camera takes a picture
• A camera is like our eyes – to “see” color, it must be able
to capture the light that is reflected from objects
• Reflected light enters the camera – passing through the
lens’s glass (which may have many elements)
• This light gets focused onto a sensor
• The sensor is sensitive to light, so it captures the light
and stores it – creating the image
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What happens inside the camera
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After light hits sensor
• Allows viewing of image on viewfinder or LCD
 Viewfinder
• can roughly match what sensor sees
• Could be like a mini tv
• Might be a reflection of the light from the lens
• Push the shutter release button – the shutter opens/closes for a
period of time
 Camera may autofocus, lock exposure, cause flash to fire, etc
• Digital information is stored on memory – the speed that it takes to
write the information to memory depends on size of image, type of
compression & compression ratio, and speed of media)
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Sensors and colors
• Sensors can’t see colors – they can only collect the brightness of the
scene
• Colored filters are used to limit range of light for each pixel
 So each pixel reads a value for the red, green, or blue to define the final
color – sometimes only one color is read, and the others need to be
interpolated
 Different sensor types have different ways that they deal with this
limitation
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How a sensor works
• The sensor is sensitive to light, so it captures the light and stores it –
creating the image – how does this work?
• Sensor is made of millions of individual light sensitive pixels (diodes)
 This sensors are arranged in a grid, or array
• Each pixel collects a charge proportionate to the intensity and
amount of light
 Pixels translate light into specific voltage values
• The strength of the charge corresponds to the brightness of the pixel
(up to a certain point)
 A pixel can only hold so much charge, if too much builds up, it could
overflow to neighboring pixels – a process called blooming – proper
exposure will eliminate most blooming, if in doubt, underexpose the
image
 Some sensors have mechanisms built in to minimize effects of blooming
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What happens with the
charge?
• Light has been collected as voltage (charge)
• Voltage information has an infinite amount of variation,
smooth transitions
 This is called ANALOG information
• The camera needs the information to be in discrete digital
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numbers to store the picture
So the sensor (or other circuitry) has to perform analog to
digital conversion
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Digital Data
• The digital data can be written to the
cameras memory, and represents the light
information that hit the sensor, but in a way
a computer can understand.
• The image sensor determines the
resolution and quality of the final image (by
the number of light-sensitive pixels that
collect information)
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Types of Sensors
• Sensors work by having light-sensitive
pixels that collect the light
• This sensor technology is relatively new
(within the last 30 years) and is still being
improved.
• Physicists are working with different
materials and making different kinds of
sensors that capture the light
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CCD Image Sensor
• CCD = Charge Coupled Device
• Grabs part of picture with each exposure
 Array arranged in mosaic or Bayer pattern
 Each pixel registers one of 3 colors
• 50% green pixels are registered, 25% (each) blue
and red registered
• Other colors must be interpolated (guessed)
 True resolution of camera is reduced because not
all the light is being recorded
• Array of pixels gather light and translate to a
voltage
 CCD sensor is just an analog device – it does not
process voltage; so additional circuitry in the
camera must do that
 Each row read one at a time (like a conveyer belt)
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Foveon CMOS Image Sensor
• CMOS = Complementary Metal Oxide Semiconductor
• Captures RGB light at each pixel; no interpolation (3 layers of
photodetectors)
 Uses properties of silicon to register light absorption at different
layers
 No interpolation is necessary – less light is wasted
 But sensor is less sensitive, so information is still lost
• Pixels in sensor include the circuitry to convert voltage to the
digital data
 done in parallel – each pixel can be processed individually and
immediately
 Can record an image more quickly (theoretically)
 Use less power because several functions are included on the
image sensor
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Which image sensor is better?
• Currently, CCD has better image quality and a
better range
 But like we said, it doesn’t do digital conversion, so it
uses more power
 It requires special production techniques – but
generally has less noise
• But, CMOS is catching up & is being used in
professional level cameras because the sensors
consume less power
 CMOS sensors are less expensive to produce
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Tomorrow
• Tomorrow we will look at how lenses affect
what light reaches the sensor – and how
that affects what image the camera sees.
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Lenses and Exposure
Lecture 05
September 15, 2005
The Lens
• Lens is the eye of the camera
 It captures and focuses the light onto the sensor
• The lens affects the quality of the image & the kinds of
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pictures that you can take
What matters:
 Quality of lens
 Amount of light it can
transmit
 Focusing range
 Amount of magnification
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Lenses: Focal Length
• Focal Length: The distance from the rear nodal
point of the lens to the point where the light rays
passing through the lens are focused onto the
image sensor
 Measured in millimeters (Film standard is 35mm)
 Think of it as the amount of a lens’s magnification
• The longer the length, the more the lens will magnify the
scene
Picture from Real World Digital Photography Book
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Focal Length
Photos from Canon Website
Canon Photo Shooting- Techniques
(Using a telephoto lens)
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Lens Aperture
• Size of the opening that admits light to the sensor, relative to the
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magnification or focal length of the lens
f-stops (denominators of fractions indicating relative size of opening)
 Each stop you open up doubles the amount of light reaching the sensor
• Maximum aperture – lets in more light – good for dim lighting
• Minimum aperture – how much light can you block from the sensor (used for
bright lighting)
 Also can increase depth-of-field
f8
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f4
f2
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Lens Speed
• Lens Speed
 Amount of light the lens transmits at maximum
aperture
 A lens with maximum aperture of f2 is “fast”
compared to a lens with max aperture of f8
which is “slow”
• Fast lens = large aperture - allows lens to transmit
more light
• Slow lens = small aperture - little light gets through
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Kinds of Lenses
• Zoom Lens
 Allows you to enlarge or reduce an image without having to get closer or
farther away
 Optical Zoom - changes the effective focal length of the lens
• Telephoto lens
 Compresses the apparent distance between objects, making them
appear to be closer together
• Wide-angle lens
 Expands apparent distance between objects, giving vast areas of
foreground, making distant objects appear to be farther away
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Wide vs. Telephoto Lenses
Photos from Canon Website
Canon Photo Shooting- Techniques
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
photo with a wide-angle lens (35 mm)
Week 2
a photo with a telephoto lens
(equivalent to 150 mm)
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Wide-angle lens
• Wide angle lenses let you shoot over a
wide range (vertically)
 But it makes things in the background appear
even further away (large depth-of-field)
• It can cause strong distortions in up-close
photos of subjects
Photos from Canon Website
Canon Photo Shooting- Techniques
Week 2
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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Telephoto Lens
• Lets far away objects appear closer
• Makes background objects appear to be
close to subjects
• Can be used to artistically blur the
background (short depth of field)
Photos from Canon Website
Canon Photo Shooting- Techniques
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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Shutter Speed
• Is measured in seconds or fractions of a
second
• The duration of time the shutter opens and
closes during an exposure process
 How long the light flows through the lens and
onto the image sensor
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Introduction to Exposure
• Exposure is the amount of light striking the sensor
• Three factors determine correct exposure
 Amount of light in scene that strikes the image sensor
 Length of time the sensor is exposed to light
 Sensitivity of the sensor
• Think of each pixel on the sensor as a little bucket that
catches photons of light as they pass through the lens.
 Bucket must fill up to a threshold point before the pixel will
register it as part of the image
• Raising or lowering the threshold mark will decrease or increase the
sensitivity of the sensor
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Exposure
• Aperture (f-stop) determines how many
photons are admitted at once (like a
funnel)
• Shutter speed determines how much
time the photons have to strike the
sensor (like a valve controlled by a
timer)
Aperture & shutter speed work together to create proper exposure
–Buckets can be filled quickly with short shutter speed and large lens opening
–Buckets can be filled slowly with long shutter speed and small lens opening
 Same exposure (same amount of light reaching the buckets) 
RECIPROCITY – equivalent exposure values
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Reciprocity
• Equivalent Exposures
EV14
Shutter
1/30th sec
f-stop
f22
1/250th sec
1/1000th sec
1/4000th sec
f8
f4
f2
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Schedule
 HW1 -- (For Friday, but bring on Tuesday)
 Write 1/2 - 1 page (single-spaced) OR make a PowerPoint presentation
of a mini biography of a famous photographer (not Ansel Adams), plus
download or bring in 2-3 pictures taken by that photographer to show
the class on Tuesdat
 Tomorrow no coordinate classes this period.
• HW2  Friday during class we will take pictures as part of Homework 2 (see
website) and experiment with the lenses
 Over the weekend - continue taking pictures as part of HW 2
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