Outline
• Image formats and basic operations
– Image representation
– Basic operations
Four Stages of Visual Processing
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Image-based stage
Surface-based stage
Object-based stage
Category-based stage
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Problems in Computer Vision
• Classification
– Edge detection
• Segmentation
• Recognition
• Motion analysis
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Digital Image Formation
• How to acquire a digital image – Digital
cameras
– The continuous spatial space is digitized into
small cells
– The color of a cell is all the photons fall into the
cell within a very short period of time
– Charge Coupled Device - CCD cameras
• An electronic memory which is able to be charged by
light
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Image Representation
• Mathematically, an image can be represented
by a 2-D matrix
– Each entry (i,j) represents the value at the
corresponding location, which is called a pixel
– The value of a pixel can have different types,
depending on the image types
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Unsigned char
Int
Float
A vector (Color image, for example)
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Image Sequence Representation
• Mathematically, an image sequence is
represented as a 3-D matrix
– At any time, it is a 2-D matrix
– A commonly used format is animated gif
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Image as a File
• Image formats
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TIFF
GIF
JPEG
PBM
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Image as a File – cont.
• Image file consists of two parts
– Header
• Type of the image
• Size of the image
• Color map
– Data
• Uncompressed
• Compressed
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PBM Format
• Portable Bitmap Utilities
– Header
• A two-letter magic number that identifies the format
type
• File parameters
– Height, width, maximum value of a pixel of the image
– Data
• In ASCII or binary, depending on the format type
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Portable Gray Map
• Binary PGM format
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P5
Width
Height
Max
Pixels as binary values
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Portable Pixel Map
• Binary PPM format
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P6
Width
Height
Max
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Programs to Read/Write Images
• These functions are based on my program
– type-def.h defines the structures
– imageio.c defines the functions to read and write
images of different types
– util.c defines functions to dynamically allocate
memory needed for an image
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Image Sequence
• There are many different kinds of formats for
movie or video sequence
– avi
– mpeg
• An easy way to generate a video sequence is
to concatenate images together
– Animated gif is such a format
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Visualization of Images
• xv
– A utility for X-window system
– Can display and convert many different kinds of
image formats
• ImageMagick package
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convert
display
animate
available at
http://www.simplesystems.org/ImageMagick/
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