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Analog and Digital
A n a l o g D i g i t a l
The term 'analog' is used because we use an analogy to describe the data. A digital device records information as a series of numbers. These numbers are then translated to represent another entity.
Analog information is mechanical. It usually offers nearly infinite precision, but limited accuracy. Digital instruments do not have as much precision as their analog counterpoints, but they tend to be much more accurate.
Analog Signal
A continuously varying signal that provides an exact representation of the signal level at any instant in time.		 Digital Signal
A signal that is represented with a predefined set of numbers or digits: a discrete representation of a signal with a stepped (not continuous) characteristic dependent on the numerical resolution of the digital system.
R E S O L U T I O N
Resolution is the number of dots available
to represent graphic detail in a given area:
on a computer screen the number of pixels per linear inch - ppi
(72 to 96 ppi is the maximum a monitor displays)
on a printer the number of dots printed in a linear inch - dpi
on a scanner the number of pixels sampled per linear inch of the scanned image- ppi
IMAGE RESOLUTION is measured in pixels per inch - ppi
PRINTER RESOLUTION is measured in dots per inch - dpi
HALFTONE FREQUENCY which determines the size of printed dots is measured in lines per inch - lpi
If an image has a resolution of 72 ppi, this means it contains 5184 pixels in a square inch
 (72 pixels wide x 72 pixels high = 5184).
Because the number of pixels in an image is fixed, when resolution decreases, the image size increases.
 Conversely, if we increase the resolution of an image, the image size (dimension) will decrease.
Higher resolutions allow for more detail and subtle color transitions in an image.

 

There are two types of computer graphics:
VECTOR BITMAP (raster)
Exist as a mathematical equation.
Mathematically defined lines and curves. 		They are rectangular grids made of little
squares (like checkerboards).
Is resolution independent
- scaling want effect image quality.		 When a bitmap picture is resized,
it often distorts the image.
Vector art consists of fills and outlines applied to a geometric description of a wireframe design. The grid of pixels. Has four basic characteristics dimension, revolution, bit depth, and color model.
Characterized by geometric precision
and a perfect focus. 		Bitmapped image can simulate photographs
and paintings because qualities of lighting
transparency and depth of field.
Because computer screens are made up of a grid of pixels,
both vector and pixel images are displayed as pixels.

Digital photographs are made up of hundreds of thousands or millions of tiny squares called picture elements - or just pixels.

Pixel is an abbreviation of the term "picture element." In digital cameras, the image sensor, which captures image information, consists of a geometric grid of pixels.

The computer divides the screen or printed page into a grid of pixels.  It then uses the values stored in the digital photograph to specify the brightness and color of each pixel by number. Controlling, or addressing a grid of individual pixels in this way is called bit mapping and digital images are called bitmaps.

In a digital camera, the light tight box comes with a light sensitive chip, usually a charge coupled device (CCD), which is the light sensitive element. Unlike film, most light sensitive chips can be reused again and again. Instead of being physically changed by the light that strikes it (the film), the chip sits in darkness inside the camera until the shutter opens and light focused by the lens strikes the chip. Tiny sensors on the chip send out a series of electrical signals that are then converted to digital for. Once those signals have been internally processed and recorded and then stored on a removable memory card or in the camera’s memory, the chip is ready to capture another image.
The lens on a digital camera performs exactly the same functions as it does on a film camera-it allows light to pass into the camera. The lens focuses the light to form a sharp image on either the film or light sensitive chip. In most cases the lens also houses the diaphragm that controls how much light strikes the film.

With all cameras the “normal” lens focal length is determined by measuring the diagonal size of the image sensor. In a 35mm camera the image sensor is the film and for years the size of the image sensor has not changed (the frame size on a piece of 35mm film is 24mm by 36mm). The diagonal measurement of a frame of 35mm film is 44mm.
The camera industry has taken this number and rounded up to 50mm for SLR cameras, and sometimes rounded down to around 38mm for point and shoot models. As a result any lens with a focal length in this range is considered to be a “normal” focal length for 35mm film cameras. Normal lenses are considered to show a field of view that is similar to what we see with our eyes.
Optical zoom simply means that the actual glass elements of the camera’s lens cover the entire zoom range offered by the camera. This is the same as any zoom lens used on a conventional film based camera.

Digital zoom is used to extend the maximum magnification of the lens beyond that which can be capture optically by the lens. A digital zoom simply crops into its largest magnification and then “stretches” that information through interpolation. Interpolation means that the computer “guesses” what additional pixels would look like and inserts them into the image. The results of digital zooming are inferior to that of the optical zoom.

 

Focal Length Comparison
35 mm Camera Digital Camera
with 1/2" chip
20mm 4.8mm
40mm 9.6mm
50mm 15mm
80mm 19mm
100mm 24mm
200mm 48mm
300mm 72mm


 
FILE SIZE
File size (kilobytes) = (resolution to square power) x With x Height x Bits 8,192
8.192 is the number of bits in a kilobyte
File format can also affect the file size of bitmapped image file.  eg. EPS file typically includes a preview image, TIFF files often include built-in compression. Also binary-encoded bitmaps are half the size of ASCII-encoded bitmaps.
 
2MP camera can produce photo quality prints up to 5x7, a 3MP up to 8x10 and a 6MP up to 13x19.


 
The shutter controls:
  • The duration of exposure
  • The exact moment when the image sensor is exposed to light
  • How subject (or camera) movement records (freezes or blurs the motion)


The numbers represent fractions of a second -"250" means 1/250 of a second.

Shutter speeds, like f numbers, decrease in a regular sequence - each speed setting is half the previous exposure time. For example 1/30 sec at F8 gives the image sensor twice as much light as 1/60 sec at F8.

Note:
When shutter speed is slower than 1/60 of a second, use tripod to avoid blur (because you are holding the camera unsteadily).

Experiment with different shutter speeds
With slow shutter speed, subject movement will record blurred, implying action, but with a loss of detail. The faster times - progressively eliminate the blur, revealing detail, but reducing the sense of movement.		 The aperture controls:
  • The amount of light the image sensor receives.
  • Depth of field - the zone of sharp focus in front of and behind the focused subject.

Each aperture setting has an "F number" which is the ratio of the diameter of the aperture (at that setting) to the focal length of the lens. So F4 really means that the aperture is one-quarter of the lens focal length.

The aperture control ring on a camera includes intermediate settings, creating a series which progressively doubles (or halves) the light that is admitted.

Note:

  • The higher the number (1.4 - 22) the smaller the hole in the lens.
  • The closer you get to your subject the shallower the depth of field becomes.
  • Depth of field increases significantly starting with f8 and higher numbers.
Shutter speed and aperture combinations
In order to record the image clearly, the image sensor must receive the right amount of light, that is, it must not be overexposed or underexposed.

Under normal light conditions it matters little whether you use a fast shutter speed with a wide lens aperture or a slow shutter speed with a small lens aperture; both give the image sensor the same amount of light.

The doubling and halving relationship of the aperture and shutter settings on the camera, allows you to combine different settings, altering the effect on the image, but admitting exactly the same quantity of light. For example, if your exposure meter indicates that your subject needs an exposure of 1/60 sec at F8, you could set your camera at 1/500 sec at F2.8, or 1/15 sec at F16 instead.

Make sure that your meter "sees" the most important areas of the subject. Take your reading from those areas, and if necessary, average out the light and dark areas.
T
R
I
P
O
D		 1/4 Blurry F22 o Darker
1/8   16 o  
1/15 11 o  
1/30 8 o  
1/60 5,6 o  
Handheld 1/125 4 o  
1/250 2.8 o  
1/500 Frozen 1.8 o Lighter
STUDY MATERIAL