CSC414ComputerSystemFundamentals

THINK BIG WE DO

U R Ihttp://www.forensics.cs.uri.edu

Digital Forensics CenterDepartment of Computer Science and Statics

Raw MediaData TypesRaw MediaData Types

Raw Media DataCapturing an aspect of the real world and digitizing it.- Organized in a files

Audio information- Voices, music, other sounds

Visual information- Still images- Photos, drawings

- Moving Images- Videos, movies, animations

- Can include audio

Storing raw media requires significant

disk space.

Audio DataAnalog sound wave is sample multiple times a second- Height of save at the instant sampled

is stored- 1000 samples per second = 1 KHz

(kilohertz)

- Audio CD sampling rate = 44.1KHz

- Height of each sample saved as:- 8-bit number for radio-quality recordings

- 16-bit number for high-fidelity recordings

- 2 x 16-bits for stereo

Stereo CD Quality1.4 Mb / sec of music

176.4 KB / sec of music31.8 MB for 3 minute song

Audio DataRaw Audio Data- Stored in files along with descriptive

information- Rate it was digitized

- Audio Interchange File Format- .aiff, .aif

- audio/aiff, audio/x-aiff

- Waveform Audio File Format- .wav

- audio/wav, audio/x-wav 010000100110111101101101011000101/44,100th of a second of stereo music

Images & Visual DataCapturing Visual Data- Camera or Scanner- CCD - Charge Coupled Device- CMOS - Complementary Metal Oxide

Semiconductor- Convert light into electronic data- Pixel - Picture Element- Each pixel is stored as one to four (or

more) bytes- Number of pixels in camera determines

number of squares- 640 x 480 pixel image requires- 307 KB for 1 byte / pixel- but limited to only 256 colors!- 1.2+ MB for 4 bytes / pixel- 8-bits per color (red, green, blue)- 8-bits for alpha channel (opacity)

Pixel

Images & Visual DataReducing Image Size- (not using compression)

- results in loss of quality

Reduce number of pixels- Results in a blocky/blurry image

Reduce number of colors- Use fewer bits or bytes for each

pixel

- Results in a grainy image

Images & Visual DataRGBA 32-bit Color- Each byte represent a

percentage of the color- 0 is 0%

- 127 is 50%

- 255 is 100%

Alpha channel- if included, determines the

transparency of the pixel

Bitmaps store each pixel- .bmp

01000010011011110110110101100010

66 111 109 98

Red Green Blue Alpha

25% 44% 43% 38%

Images & Visual DataObject and Vector Images- Created by drawing packages or output

from spreadsheet data graphs

- Composed of lines and shapes in various colors

- Computer translates geometric formulas to create the graphic

- Storage space depends on image complexity- Number of instructions to create lines,

shapes, fill patterns

0

25

50

75

100

20072008

20092010

Region 1 Region 2

Video DataVideo and Movie Files- Can be uncompressed, but

require SIGNIFICANT disk space!

(300 s) x (1.2 MB per frame) x (30 fps)

Five minutes of Standard Definition (SD) video at 30 frames per second:

11 GB for 5 minutes!THINK BIG WE DO

U R Ihttp://www.forensics.cs.uri.edu

Digital Forensics CenterDepartment of Computer Science and Statics

Raw Media Data TypesRaw Media Data Types