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Robot Vision Module
Dott. Emanuele Menegatti([email protected])
Intelligent Autonomous Systems LabUniversity of Padua
ITALY
Based on course notes of Prof. Bob Fisher Edinburgh University - UK
…a Computer Vision example...
Sorting parts on a conveyor belt
... A Robot Vision example... Navigation and Obstable avoidance
?
!! Real Time – Real World !!
Physics of Vision
Illumination
The sensors…
Humans Eyelid Iris Lens Retina Optical Nerve
Robots Shutter Iris Lens CCD TV Cable
The retina…
Horizontal cell
Bipolar cellAmacrine cell
Ganglion cell
Optical Nerve
Light
http://webvision.med.utah.edu/
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Camera Evolution
Pinhole Camera
http://www.kodak.com/global/en/consumer/education//lessonPlans/pinholeCamera/http://www.pinhole.org/about/index.cfm
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Camera Evolution The lens Introduced to collects more
lights
The film Introduced to store the image The CCD Introduced to acquire directly a
digital image (higher performances for certain applications)
How to capture colours
The original (left) image
is split in a beam splitter
Thin Lens terminology
Optical Axis
Lens Axis
Focal point(Secondary)
Focal length
(in a real camera: Focal length = the distance between the equivalent center of the lens
and the image plane)
Ray TracingWe will consider a simple system composed of a single thin lens,
there are simple rules we have to follow to ray-trace:1. Rays travel in straight lines and change directions only when
they encounter a discontinuity of the refractive index
2. It is conventional to have the object on the left of the optical system and the image will form on the right
3. All rays emanating from a single point in space must converge on a single point in the image plane (definition of focus)
4. Any ray entering the lens parallel to the axis on one side goes through the focus point on the other side
5. Any ray entering the lens from the focus point on one side emerges parallel to the axis on the other side
How to look at Vision? Low Level Vision:
Middle Level Vision:
High Level Vision:
Image Level Properties
Properties of World
Properties of Actual Objects
–Feature detection–Lightness–Geometry & Shape
–Stereo & 2½D sketch–Motion & Optical Flow–Shape from Shading
–Object Representation–Object Recognition–Geometric Invariance
Basic Optics
Images’ FileComposed of: Image File Header
Self-description of the image Image dimensions Image type Date of creation Program that created the image
Image data Some image formats can handle only limited types of images (bynary or monocrome), but the current formats are evolving toward Multimedia contents
Formati di ImmagineDue tipi fondamentali di immagini o meglio due modalità grafiche per rappresentare le immagini:
Bitmap L’immagine viene descritta dando il colore pixel per pixel
Vettoriale Oggetti presenti nell’immagine descritti in termini matematici
BitmapCaratteristiche: Risoluzione (ppi) Profondità di colore
Compressione Lossy (JPEG) Lossless (GIF)
Adatto per sfumature di colore
Bitmap (2)
GIF (Lossless)Graphics Interchange Format
JPEG (Lossy)Joint Photographic Expert Group
Bitmap (3)GIF
GIF87 256 colori
GIF89 Trasparenza Interlacciamento Immagini multiple (gif animate)
Created by CompuServe Inc.
JPEG Non ha limiti di colore
Adatto per foto Una sola immagine per file
Header può contenere preview
Immagini Vettoriali
Caratteristiche: Dimensione immagine Descrizione matematica
Compatta Non adatta per foto o immagini ricche di dettagliImmagine vettoriale Bitmap (FACILE)
Bitmap Immagine Vettoriale (DIFFICILE)
PBM (Portable Bit Map) Family of formats:
PBM Supports monochrome bitmaps (1 bit per pixel). PGM Supports greyscale images PPM Supports full-color images PNM Supports content-independent manipulations on
any of the three formats listed above
P3 # magic number# example from the man page 4 4 # cols & rows15 # maxval0 7 0 015 0 15 0 0 0 0 15
TIFF (Tag Image File Format) Supports multiple images with 1 to 214 bit depth
Can be lossy or lossless Very general and very complex Used by scanners Created by Aldus Corp.
PostScript (ps, eps) Store image data using ASCII characters (7-bit ASCII code)
Used for graphics displays and printer
Newer versions include JPEG compression
Used to include graphics or images in a document
MPEG (Motion Picture Expert Group)
Stream-oriented encoding for video Contains video, text, graphics Created by an international group of industry and governments
Uses Spatial and Temporal Redundancy It is evolving:
MPEG-1: 0.25Mbps (audio) 1.25Mbps (video) MPEG-2: 15Mbps good for TV Future version will recognizes objects and generate their images
The Difference Between CCD and CMOS CCD high-quality, low-noise images. CMOS more flexible (every pixel can be read independently) The light sensitivity of a CMOS chip is lower (Many of the
photons hitting the chip hit the transistors instead of the photodiode)
CCDs consume 100 times more power than an equivalent CMOS sensor.
CMOS extremely inexpensive compared to CCD sensors (Chips can be fabricated on any standard silicon production line)
CCD sensors produced for a longer period of time, so they are more mature. They tend to have higher quality pixels, and more of them.
Depth of Field...
… depends on: Shutter Opening Sensitive Element
Focal Length of the lens
Distance of the object
Region of confusion
Hyperfocal distance
Depth of Field
Task: Sort Parts Vision Goal: Describe and Identify
Constraints: Flat Shapes Sit flat Different Areas Opacity Serially delivered
Camera
Synch
Silhouette
Detector
Counter
Size Comparator
Threshold
Threshold