Creating Digital Pictures
A traditional photograph is an analog representation of an image.
Digitizing a picture is the act of creating picture elements (pixels) to represent the image.
The process is similar to the sampling of analog audio The more pixels, the better the quality The more bits for each pixel, the closer the
approximation The human eye can be tricked into filling in
the missing pieces
Resolution
The number of pixels The higher the resolution, the clearer
the picture Increased resolution allows you to zoom
in and see more detail Higher resolution increases the size of
the file in memory
How much space?
For each pixel you have to store a color or grey scale.
Resolution 300x200 = 60,000 pixels 8 bit greyscale (256 tones) – 60KB 24 bit true color – 180KB (3 bytes per
pixel)
Graphics File Formats
Raster Graphics Stores information on a pixel-by-pixel
basis BMP, GIF, JPEG, PNG
Vector Graphics Stores a description of shapes in the
picture Scalable Vector Graphics (SVG)
JPEG vs GIF
JPEG Joint Photographic Experts Group
Forgent Networks claims patent on key algorithm 24 bit color Lossy compression
Cleverly removes portions of picture that humans won’t see Very good for pictures, “realistic” scenes Allows use to select amount of compression
GIF (Graphics Interchange Format) Patented by Compuserve 256 colors Lossless compression Good for line drawings, clip art
Digital Cameras
Much like a normal camera in terms of optics
Has advantage of knowing what a picture looks like immediately
Digital Pictures
Image is acquired by absorbing reflected light and recording the wavelengths (very similar to sampling audio)
The sensor takes the place of the film
Stored in proprietary RAW format before download to computer
Sensor sends digital signals to be processed and stored in non-volatile memory
Megapixels?
What does it mean? Amount of sensor information Allows for more pixels at maximum
resolution Why is 5 megapixels better than 3 or
4? Can they really zoom in on pictures
like on CSI?
Displaying Images
Display types CRT LCD Gas Plasma
Typical resolutions 800x600 1024x768 1152x864 1280x1024
4 to 3 ratio Movies are 16:9
Refresh rate Interlacing
Graphics Card
15”
12”19”
Graphics Cards
Hardware that connects monitors to your PC Have processors, memory, clocks Almost sub-computers Controls resolution and refresh rate
Drivers Software that allows graphics cards to interface with
monitors Specific to Operating Systems
Linux often has worse support because fewer people use it
Some card include “tuners” for television NTSC
MPEG Compression MPEG-1
video resolution of 352-by-240 at 30 frames per second (fps) quality slightly below the quality of conventional VCR videos
MPEG-2 offers resolutions of 720x480 and 1280x720 at 60 fps full CD-quality audio sufficient for all the major TV standards, including NTSC, and even
HDTV MPEG-2 is used by DVD-ROMs. MPEG-2 can compress a 2 hour video
into a few gigabytes decompressing an MPEG-2 data stream requires only modest
computing power, encoding video in MPEG-2 format requires significantly more processing power
MPEG-4 graphics and video compression algorithm standard that is based
on MPEG-1 and MPEG-2 and Apple QuickTime technology Wavelet-based MPEG-4 files are smaller than JPEG or QuickTime
files designed to transmit video and images over a narrower bandwidth
and can mix video with text, graphics and 2-D and 3-D animation layers