P. 1

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How a Digital Camera works

• Digital cameras ???? are very much like the 35
  mm film cameras.
• Both contains
• a lens ?? ,
• an aperture,
• and a shutter.

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Digital Camera ?????

• ?????(Digital Camera),??????,?????????????????????
  ???????????????????????????????????,??????????????
  ????????(CCD)???????????,?????????????????

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Digital Camera

• DC with compact flash card ?????

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How a digital camera works

• The lens ??
• brings light from the scene into focus inside
  the camera so it can expose an image.
• The aperture ??
• is a hole that can be made smaller or larger to
  control the amount of light entering the camera.
• The shutter ?? (???????)
• is a device that can be opened or closed to
  control the length of time the light enters.

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Camera Body
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Camera top view
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• DC use a solid-state device called an image
  sensor, usually a charge-couple device (CCD)
  ?????? .

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• When the shutter opens, light strikes the image
  sensor to form the image.

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• When the shutter opens, each pixel on the image
  sensor records the brightness of the light
• The more light that hits a pixel, the higher the
  charge it records.
• When the shutter closes, the charge from each
  pixel is measured and converted into a digital
  number.

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From black and white to Colour

• Daylight is made up of red, green, and blue light
• Placing red, green, and blue filters over
  individual pixels on the image sensor can create
  color images
• Bayer pattern used on many image sensors

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• Colored filters cover each photosite on the image
  sensor so the photosites only capture the
  brightness of the light that passes through.

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Aperture (??)

• Size of the lens opening which controls the
  brightness of the light that reaches the film
• It is indicated by its f-number or f-stop.
• f / n focal length / dia. of aperture
• ??? ???? / ????
• e.g. a 50mm lens, if the diameter of an aperture
  is 36mm, then
• f-stop 50/36 1.4

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Aperture (??)

• Larger the f-stop value, smaller the aperture
  diameter.
• Smaller the aperture size, the more that a scene
  will be sharp from near to far, that is a wider
  depth of field ??.

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Aperture size
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Aperture size
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Aperture size

• use large aperture for dim image or focus object
• e.g. Portraits

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Depth of field (??)

• In front of and behind the true focus point,
  there is a zone where the image is acceptably
  sharp. This zone of sharp focusing is called the
  "Depth of Field ??.

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Shutter Speed (??)

• It controls the duration of time that exposed to
  light
• faster the shutter speed, shorter the exposure
  time
• faster the shutter speed, the more likely a
  moving object will be sharp.
• used to freeze a speeding object

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Combination of Aperture Shutter
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The Shutter ?? Controls Light and Motion

• Slower shutter speeds let more light strike the
  image sensor making an image lighter, e.g. 1/30.
• Faster shutter speeds let less strike it and make
  the image darker, e.g. 1/250.

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• Left picture the shutter was left open longer
• This longer exposure time has made the image
  lighter, e.g. 1/30.

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The shutter and motion

• Shutter speeds can control whether a moving
  subject will appear in your image sharp or
  blurred.
• The longer the shutter is open, the more a moving
  subject will be blurred ?? in the picture
• Also, the longer it's open the more likely you
  are to cause blur by moving the camera slightly.

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• A fast shutter speed (left) opens and closes the
  shutter so quickly a moving subject doesn't move
  very far during the exposure
• a slow speed (right) can allow moving objects to
  move sufficiently to blur their image on the
  image sensor.

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The Aperture ?? Controls Light and Depth of Field
??

• The aperture diaphragm is a ring of overlapping
  leaves within the camera lens
• It adjusts the size of the opening in the lens
  through which light passes to the image sensor.
• As it changes size, it affects both the exposure
  of the image and the depth of field in which
  everything is sharp.

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Aperture ??

• The larger the aperture opening, the more light
  reaches the image sensor in a given period of
  time. The more light, the lighter the image.
• Like shutter speed, aperture also affects the
  sharpness of your picture, but in a different
  way.

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• Larger aperture
• can make part of an image stand out sharply
  against a softer background. This emphasizes the
  sharpest part of the image

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Aperture ?? and Depth-of-field??

• Aperture is expressed as F-stop, e.g. F2.8 or
  f/2.8. The smaller the F-stop number (or
  f/value), the larger the lens opening (aperture).
  
• F
• The smaller the aperture you use, the greater the
  area of a scene that will be sharp.

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• Small Aperture keeps everything sharp from the
  foreground to the background.

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• Fast shutter speed to prevent blur caused by
  subject or camera movement.

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• Motion in a scene can be frozen depending on the
  shutter speed.
• Blur can be used to evoke ?? a feeling of motion
  as in this shot of a waterfall.

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• Shallow depth of field can focus attention on a
  foreground subject by making the background less
  sharp.

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• The shutter speed froze the central dancer but
  was slow enough to blur the others. This makes
  the central dancer the most important person.

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Image Resolution ???

• The resolution determines the number of pixels to
  produce a picture.
• More pixels in a picture enable you to print a
  larger print.
• More pixels,
• the larger the file.

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• Resolution determines the size of the image.

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Image Compression

• More pixels, the larger the file.
• To reduce file size, we need compression.
• The more an image is compressed , the lower the
  image quality
• Balance the tradeoffs between image size
  (resolution), compression level, image quality
  and possible print size.

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• Look at the shirt color and the dark areas of his
  shirt. In the right image you can see jagged
  lines and blocks of color starting to appear.

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Which one is heavy compression ?
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Image File Format

• Most digital cameras offer three formats
• Compression ratio
• JPEG (.jpg), 101
• TIFF (.tif), 11
• and RAW format. 21
• The most commonly used format is the JPEG format.