Outline Image formats and basic operations Image representation

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

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

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

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) 11/13/2018 Visual Perception Modeling

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

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

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 11/13/2018 Visual Perception Modeling

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 11/13/2018 Visual Perception Modeling

Visual Perception Modeling Portable Gray Map Binary PGM format P5 Width Height Max Pixels as binary values 11/13/2018 Visual Perception Modeling

Visual Perception Modeling Portable Pixel Map Binary PPM format P6 Width Height Max 11/13/2018 Visual Perception Modeling

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

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

Visualization of Images xv A utility for X-window system Can display and convert many different kinds of image formats ImageMagick package convert display animate available at http://www.simplesystems.org/ImageMagick/ 11/13/2018 Visual Perception Modeling