Image Representation

1
Image Representation
2
Image Representation image - a
two-dimensional light intensity function f(x,y)
- x and y denote spatial coordinates
- the value of f(x,y) is proportional to the
brightness of the image at position
(x, y)
digital image - an image that has been
discretized in both brightness and
spatial representation
3
Scanners- small flatbed to large continuous line
4
Digitizer
Digitizer- manual input, output is in vector
format. Process is digitizing.
5
Digital image - represented as a
matrix, fxy, whose row and column indices
identify a point in the image - a matrix
element corresponds to the gray level
(brightness) at that point - points in this
matrix are called picture elements, pixels or
pels.
Often, images are dyadic (square) and have rows
and columns which are a power of two to
facilitate processes which use a divide and
conquer strategy.
6
Image Coordinate System
N
(0,0)
(m,n)
M
7
Image Display
Physical Pixels - dots displayed on the output
device - hardware dependent
Logical Pixels - mathematical points associated
with the data they represent - occupy no
particular area on the display
8
Image Display
Physical Pixels - smallest independently
programmable element in the display
- monitor resolution (number of physical
pixels in the display)
- pixel depth (number of colors which can be
displayed at a time)
9
Image Display
CRT Cathode Ray Tube An electronic screen lined
with phosphorous material which glows when struck
by a stream of electrons. A set of electron guns
at the back of the monitor produce a controlled
stream of electrons. The intensity of the
electron beam determines the color and brightness
of each pixel on the screen
10
(No Transcript)
11
There are three electron guns, to control the
display of red, green and blue light.
The surface of the CRT is arranged to place the
color dots in a specific pattern.
12
Image Display
Logical Pixels - spatial resolution - pixel
depth (brightness/color quantization)
Binary - 1 bit data Greyscale - 8 bit
data Pseudocolor - 8 bit data w/ LUT True Color -
24 bit data
13
256 Color Image Display
System Color Palette (LUT)
Pixel value (0-255)
0
1
2
(m,n)
3
4
5
...
255
8 bit gray scale
14
Color Palette (LUT)
Index
Color
R
G
B
0
0
0
0
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
5
5
5
5
...
...
...
...
255
255
255
255
8 bit gray scale
15
Image Display
Image Color Palette (LUT)
Pixel value (0-255)
0
1
2
5
3
4
255 0 0
5
...
255
8 bit pseudocolor
16
Image Data Files
Vector Data
Bitmap Data
17
Image Data Files
Common Bitmap File Formats
BMP - Microsoft Windows Bitmap PBM,PGM,PPM -
Pbmplus RAS, SRF - Sun Raster File TIFF - Tag
Image File Format GIF - Graphics Interchange
Format PNG - Portable Network Graphic Format JPG
- Joint Photographic Experts Group
18
Image Data Files
Bitmap Data Files
19
Image Data Files
Bitmap Data Files
20
Image Data Files
PBM, PGM, PPM Files
21
Image Data Files
PBM, PGM, PPM File Types
ASCII data
binary data
Black and white
P1
P4
Grayscale
P2
P5
Color
P3
P6
22
Remote Sensing Data Files
Common File Formats
Landsat (MSS) Landsat Thematic Mapper
(TM) SPOT NOAA Advanced Very High Resolution
Radiometer (AVHRR) NASA Airborne
Terrestrial Applications Server (ATLAS) Digital
Globe, Inc. (QuickBird) NASA JPL Airborne
Visible/Infrared Imaging Spectrometer
(AVIRIS)
23
Remote Sensing Data Files
Common Bitmap File Formats
Landsat TM .IMG files are all 8-bit binary
images. The file architecture is the same as that
of any common image file the first byte is the
first pixel of the first line, the second byte is
the second pixel of the first line,.(the first
pixel in the second line of image 1 is the 2049th
byte)