Image Representation Image Representation image a twodimensional light

Image Representation

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

Scanners- small flatbed to large continuous line

Digitizer- manual input, output is in vector format. Process is digitizing.

Digital image - represented as a matrix, f[x][y], 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.

Image Coordinate System N (0, 0) (m, n) M

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

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)

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

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.

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

256 Color Image Display Pixel value (0 -255) (m, n) System Color Palette (LUT) 0 1 2 3 4 5. . . 8 bit gray scale 255

Color Palette (LUT) Index: Color: R G B 0 1 2 3 4 5 . . . 255 255 8 bit gray scale

Image Display Pixel value (0 -255) 5 Image Color Palette (LUT) 0 1 2 3 4 5 255. . . 8 bit pseudocolor 255 0 0

Image Data Files Vector Data Bitmap Data

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

Image Data Files Bitmap Data Files: Header Bitmap Data Palette (LUT) Bitmap Data

Image Data Files Bitmap Data Files: May include info such as: • File type • Number of Rows & Cols • Pixel Depth • Compression Technique Header Bitmap Data • Pixel Values

Image Data Files PBM, PGM, PPM Files: ASCII header includes: • File type • Number of Rows & Cols • Max possible pixel value • optional comments # Header Bitmap Data • Pixel Values in either ASCII or Raw (binary) format

Image Data Files PBM, PGM, PPM File Types: ASCII data binary data Black and white P 1 P 4 Grayscale P 2 P 5 Color P 3 P 6

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. (Quick. Bird) NASA JPL Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)

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 2049 th byte)