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Intelligent Vision Systems
Intelligent Vision Systems
Image Geometry and AcquisitionImage Geometry and Acquisition
ENT 496ENT 496
Ms. HEMA C.R.Ms. HEMA C.R.
Lecture 2.
2Hema-ENT 496 -Lecture 2
Road MapRoad Map
Image Formation
Image Geometry
Image Sampling
Image Quantization
Image Acquisition
Image Definitions
3Hema-ENT 496 -Lecture 2
Image FormationImage Formation Image formation in the eye and the
camera Understanding function of the human
eye provides insight into Intelligent Vision System solutions
Biological vision is the process of using light reflected from the surrounding world as a way of modifying behavior
4Hema-ENT 496 -Lecture 2
Image Formation in the eye
Image Formation in the eye
Light enters through cornea Passes through aqueous humor, the
lens and vitreous humor Finally forms an image on the retina Lens adjusts and focus image
directly on retina Retina is a complex tiling of
photoreceptors known as rods and cones
When stimulated by light they produce electrical signals that are transmitted to the brain by the optic nerve
Refer: http://homepages/inf.ed.ac.uk/rbf/CVonline/
5Hema-ENT 496 -Lecture 2
Image formation :Pin hole camera
Camera is
analogous to
the eye Pin hole camera
has a small hole
through which
light enters before forming an inverted image Pin hole cameras are modeled by placing
image plane between focal point of the camera and the object so that image is not inverted
6Hema-ENT 496 -Lecture 2
Image GeometryImage Geometry
Image Formation has two divisions
– Geometry of image formation
– Physics of light [brightness of point]
Image geometry determines where a world point is projected on the image plane
7Hema-ENT 496 -Lecture 2
Image GeometryImage Geometry
Object point is represented by x, y and z 3D co-ordinates.
Image plane is parallel to x and y axis [world] at a distance f [focal length]
z
x`
y`
y (x,y,z)
(x`, y`)
Object Point
f r
r`x
y
22 yxr 22 yxr
8Hema-ENT 496 -Lecture 2
Image GeometryImage Geometry
r
r
y
y
x
xr
r
z
f
z
x`
y`
y (x,y,z)
(x`,y`)
Object Point
f r
r`x
y
yz
fy
xz
fx
y
y
z
fx
x
z
f
Mapping of three dimensions onto two dimension is called perspective projection
9Hema-ENT 496 -Lecture 2
Image SamplingImage Sampling Continuous images are sampled to convert them to
digital form Each image sample is called a pixel [picture
element] Sampling is the process of representing a continuous
signal by a set of samples taken at discrete intervals of time [sampling interval]
Continuous SignalSampled Signal
Sampling Frequency Tf s 1
10Hema-ENT 496 -Lecture 2
Original Image
Sampled Image
Reconstructed Image
Image SamplingImage Sampling
11Hema-ENT 496 -Lecture 2
Quantization is the process of converting analog pixel intensities to discrete valued integer numbers
Quantization involves assigning a single value to each sample values in such a way that the image reconstructed from quantized values is good
Image QuantizationImage Quantization
12Hema-ENT 496 -Lecture 2
Image QuantizationImage Quantization
550 x 413 pixels 49868 colors
8 colors
13Hema-ENT 496 -Lecture 2
Image QuantizationImage QuantizationFrom 600x400, 32 bits image
To 600x400, 2 bits image (4 colors)
To 600x400, 4 bits image (16 colors)
14Hema-ENT 496 -Lecture 2
Image AcquisitionImage Acquisition Image acquisition is the first stage of a vision
system Acquired Image is dependent on
– Nature of sensing deviceVidicon, CCD, infra red , grayscale , color
– Properties of the deviceSensitivity, resolution, lenses, stability , focus
– The lighting of the sceneShadows, excessive reflection, poor contrast
– The environmentDust, fog, humidity
– The reflective properties of the objectsTexture, color, specularity
15Hema-ENT 496 -Lecture 2
Image AcquisitionImage Acquisition
Two Dimensional Images Three Dimensional Images
16Hema-ENT 496 -Lecture 2
Image AcquisitionImage Acquisition
Acquisition [capture] of 2D Images
– Monochrome or ColorAnalog Cameras Digital CCD CamerasDigital CMOS CamerasVideo Cameras [Analog and
Digital]
17Hema-ENT 496 -Lecture 2
Image AcquisitionImage Acquisition
Methods of acquisition for 3D
– Laser Ranging Systems
– Structured Lighting Methods
– Moire Fringe Methods
– Shape from Shading Methods
– Passive Stereoscopic Methods
– Active Stereoscopic Methods
18Hema-ENT 496 -Lecture 2
Image CapturingImage Capturing A basic image capture system
contains a lens and a detector. Film detects far more visual information than is possible with a digital system.
With digital imaging, the detector is a solid state image sensor called a charge coupled device...CCD for short
On an area array CCD, a matrix of hundreds of thousands of microscopic photocells creates pixels by sensing the light intensity of small portions of the image
19Hema-ENT 496 -Lecture 2
Image CaptureImage Capture To capture images in color, red,
green and blue filters are placed over the photocells.
Film scanners often use three linear array image sensors covered with red, green and blue filters.
Each linear image sensor, containing thousands of photocells, is moved across the film to capture the image one-line-at-a-time.
20Hema-ENT 496 -Lecture 2
Image DefinitionsImage Definitions
Pixel – A sample of the image intensity quantized to an integer value
Image – A two dimensional array of pixels Pixel
– Row and column indices [ i, j] are integer values
– Pixels have intensity values 0 to 255 grayscale images RGB value [vector value] color
images
21Hema-ENT 496 -Lecture 2
Pixel ArrayPixel Array
Pixel [4,4] ↓i →j
22Hema-ENT 496 -Lecture 2
Pixel Concept MapPixel Concept Map
23Hema-ENT 496 -Lecture 2
PixelPixel The quality of a scanned
image is determined by pixel size, or spatial resolution; and by pixel depth, or brightness resolution
This relates to the two basic steps in the digital capture process:
In step one, sampling determines pixel size and brightness value.
In step two quantization determines pixel depth
24Hema-ENT 496 -Lecture 2
Image File FormatsImage File Formats
Images are stored in a computer in one of the following formats, depending on the application of the images stored.
– Tagged Image Format [.tif]– Portable Network Graphics [.png]– Joint Photographic Experts Group
[.jpeg, .jpg]– Bitmap [.bmp]– Graphics Interchange Format [.gif]– Raster Images [.ras]– Postscript [.ps]
End of Lecture 2
Intelligent Vision Systems
Intelligent Vision Systems