1. Outline Image formats and basic operations Image representation

2. Four Stages of Visual Processing
Image-based stage
Surface-based stage
Object-based stage
Category-based stage
11/13/2018
Visual Perception Modeling

3. Problems in Computer Vision
Classification
Edge detection
Segmentation
Recognition
Motion analysis
11/13/2018
Visual Perception Modeling

4. 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
11/13/2018
Visual Perception Modeling

5. Visual Perception Modeling
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
Unsigned char
Int
Float
A vector (Color image, for example)
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Visual Perception Modeling

6. 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
11/13/2018
Visual Perception Modeling

7. Visual Perception Modeling
Image as a File
Image formats
TIFF
GIF
JPEG
PBM
11/13/2018
Visual Perception Modeling

8. Visual Perception Modeling
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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Visual Perception Modeling

9. Visual Perception Modeling
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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Visual Perception Modeling

10. Visual Perception Modeling
Portable Gray Map
Binary PGM format P5
Width
Height
Max
Pixels as binary values
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Visual Perception Modeling

11. Visual Perception Modeling
Portable Pixel Map
Binary PPM format P6
Width
Height
Max
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Visual Perception Modeling

12. 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
11/13/2018
Visual Perception Modeling

13. Visual Perception Modeling
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
11/13/2018
Visual Perception Modeling

14. Visualization of Imagesxv
A utility for X-window system
Can display and convert many different kinds of image formats
ImageMagick package
convert
display
animate
available at
11/13/2018
Visual Perception Modeling