Transcript Digital Cameras - The Daley Journal

Digital Cameras
Basic Info on Operations
Class Web Quest
How do digital cameras work?
Digital Cameras convert analog
information (represented by a
fluctuating wave) into digital information
(represented by ones and zeros, or
bits).
CDs, DVDs, HDTV, MP3s and DVRs
are all built around the same basic
process
What’s the difference b/w a digital
camera and a regular film camera?
Film cameras depend on chemical and
mechanical processes
Film cameras do not even need electricity
Digital Cameras have a built in computer which
record images electronically
What happens when a
Digital Cameras takes a picture?
Once a pic is taken the image /pic must be
converted into a form the computer
recognizes…bits and bytes
A digital pic is just a long string of pixels …1s
and 0s
– All of these pixels make up the image
To help the process along…
A Digital Cameras has different lenses that help
focus the light to create the image of a scene
A 35 mm camera would focus the light onto a
piece of film….a Digital Cameras focus the light
onto a semi-conductor device that records the
light electronically
– A computer breaks this info down into digital data
What breaks down the info
into digital data?
A sensor converts the light into electrical charges
Digital Cameras use CCDs (Charged Couple Devices)
or CMOS (Complementary Metal Oxide Semiconductor)
– Both convert light into electrons
– Value is read of each cell in the image
– Both operate similarly converting the light into readable form
What’s the real difference
Because each pixel on a
CMOS sensor has several
transistors located next to it,
the light sensitivity of a
CMOS chip is lower. Many of
the photons hit the
transistors instead of the
photodiode.
CMOS sensors traditionally
consume little power. CCDs,
on the other hand, use a
process that consumes lots
of power. CCDs consume as
much as 100 times more
power than an equivalent
CMOS sensor.
CCD sensors create highquality, low-noise images.
CMOS sensors are
generally more
susceptible to noise.
CCD sensors have been
mass produced for a
longer period of time, so
they are more mature.
They tend to have higher
quality pixels, and more of
them.
Confused?
Although numerous differences exist
between the two sensors, they both play
the same role in the camera -- they turn
light into electricity.
To understand how a digital camera
works, you can think of them as nearly
identical devices.
What else is important in a
Digital Cameras?
Resolution
– The amount of detail that the camera can
capture and it is measured in pixels.
– The more pixels a camera has, the more
detail it can capture and the larger pictures
can be without becoming blurry or "grainy."
Common Resolutions
256x256 - Found on very cheap cameras, this resolution is so low that the picture quality is
almost always unacceptable. This is 65,000 total pixels.
640x480 - This is the low end on most "real" cameras. This resolution is ideal for e-mailing
pictures or posting pictures on a Web site.
1216x912 - This is a "megapixel" image size -- 1,109,000 total pixels -- good for printing
pictures.
1600x1200 - With almost 2 million total pixels, this is "high resolution." You can print a 4x5
inch print taken at this resolution with the same quality that you would get from a photo lab.
2240x1680 - Found on 4 megapixel cameras -- the current standard -- this allows even
larger printed photos, with good quality for prints up to 16x20 inches.
4064x2704 - A top-of-the-line digital camera with 11.1 megapixels takes pictures at this
resolution. At this setting, you can create 13.5x9 inch prints with no loss of picture quality.
How do Digital Cameras
capture color?
Photosets are blind
Photosets only keep track of the total intensity of
light that strikes the surface
To get full color of an image, most sensors use
filtering to look at the light in its three primary
colors
All three colors get recorded and combined to
create the full spectrum
Capturing Color
Beam splitter – directs light to different sensors and each sensor only responds to one of the
primary colors
Rotate – all three colors (red, green , blue) get rotated in front of a single sensor; 3 separate
images get recorded
Color filter array – most economical and practical method used to permanently place a filter over
each photosite.
– Sensor gets broken up into r,g, b pixels
Bayer filter pattern
– Most common and alternates a row of red and green filters with a row of blue and green
filters.
– [pixels are not evenly divided (as many green as there are blue and red combined)
• Why?
• Human eye is not a sensitive to all three colors
• Necessary to include all of green so as to create an image that they eye will perceive a
true color
Exposure & Focus
digital camera has to control the amount
of light that reaches the sensor.
The two components it uses to do this,
the aperture and shutter speed, and
are also present on conventional
cameras.
Exposure & Focus
Aperture: The size of the opening in the
camera. The aperture is automatic in most
digital cameras, but some allow manual
adjustment to give professionals and
hobbyists more control over the final image.
Shutter speed: The amount of time that light
can pass through the aperture. Unlike film,
the light sensor in a digital camera can be
reset electronically, so digital cameras have a
digital shutter rather than a mechanical
shutter
Exposure & Focus
Aperture and shutter speed work together to
capture the right amount of light needed to make
a good image
The camera also adjusts the lenses to control
how the light is focused on the sensor.
Most Digital Cameras use auto focus lenses
Focal Length
This is the biggest difference between a digital camera
and a regular conventional camera
So what is focal length…
– The distance between the lens and the surface of the sensor
– This determines the magnification (zoom)
– Increasing the focal length increases the zoom /
magnification and vice versa
Digital Camera Lenses
Fixed-focus, fixed-zoom lenses These are the kinds of lenses on
disposable and inexpensive film
cameras -- inexpensive and great for
snapshots, but fairly limited.
Digital Camera Lenses
Optical-zoom lenses with automatic
focus –
Similar to the lens on a video camcorder,
these have "wide" and "telephoto" options
and automatic focus. The camera may or may
not support manual focus. These actually
change the focal length of the lens rather
than just magnifying the information that hits
the sensor.
Digital Camera Lenses
Digital-zoom lenses With digital zoom, the camera takes pixels from the
center of the image sensor and interpolates them to
make a full-sized image. Depending on the resolution
of the image and the sensor, this approach may
create a grainy or fuzzy image. You can manually do
the same thing with image processing software -simply snap a picture, cut out the center and magnify
it.
Digital Camera Lenses
Replaceable lens systems –
These are similar to the replaceable
lenses on a 35mm camera. Some digital
cameras can use 35mm camera lenses.
Storage
Early generations of digital cameras had
fixed storage inside the camera.
You needed to connect the camera
directly to a computer with cables to
transfer the images.
Storage
Today's cameras are capable of
connecting through serial, parallel,
SCSI, USB or FireWire connections
They usually also use some sort of
removable storage device.
Storage
Digital cameras use various storage systems.
These are like reusable, digital film, and they
use a caddy or card reader to transfer the
data to a computer.
Many involve fixed or removable flash
memory.
Digital camera manufacturers often develop
their own proprietary flash memory devices,
including SmartMedia cards, CompactFlash
cards and Memory Sticks.
Storage
Removable storage devices include:
– Floppy disks
– Hard disks, or microdrives
– Writeable CDs and DVDs