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Image Representation - Computer Graphics and Image Processing - Lecture Slides, Slides of Computer Graphics

Aligarh Muslim UniversityComputer Graphics

Main points of this lecture are: Image Representation, Pixel Values, Image Acquisition, Notions of Illumination, Line of Image Sensors, Collections of Sensors, Image Sampling, Analogue Signal, Spatial Resolution, Intensity Level Resolution

Typology: Slides

2012/2013
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Image Representation
•Before we discuss image acquisition recall that a
digital image is composed of M rows and N columns
of pixels
each storing a value
•Pixel values are most
often grey levels in the
range 0-255(black-white)
•We will see later on
that images can easily
be represented as
matrices
col
row
f (row, col)
Images taken from Gonzalez & Woods, Digital Image Processing (2002)
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Download Image Representation - Computer Graphics and Image Processing - Lecture Slides and more Slides Computer Graphics in PDF only on Docsity!

Image Representation

  • Before we discuss image acquisition recall that a digital image is composed of M rows and N columns of pixels each storing a value
  • Pixel values are most often grey levels in the range 0-255(black-white)
  • We will see later on that images can easily be represented as matrices

col

row

f (row, col)

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Acquisition

  • Images are typically generated by illuminating a scene and absorbing the energy reflected by the objects in that scene
    • Typical notions of illumination and scene can be way off: - X-rays of a skeleton - Ultrasound of an unborn baby - Electro-microscopic images of molecules Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Sampling And Quantisation

  • A digital sensor can only measure a limited number of samples at a discrete set of energy levels
  • Quantisation is the process of converting a continuous analogue signal into a digital representation of this signal

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Sampling And Quantisation

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Sampling And Quantisation (cont…)

  • Remember that a digital image is always only an approximation of a real world scene

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Representation

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Representation

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Image Representation

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Spatial Resolution (cont…)

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Spatial Resolution (cont…)

1024 * 1024 512 * 512^ 256 * 256

Images taken from Gonzalez & Woods, Digital Image Processing (2002) 128 * 128 64 * 64 32 * 32 Docsity.com

Intensity Level Resolution (cont…)

128 grey levels (7 bpp) 64 grey levels (6 bpp)^ 32 grey levels (5 bpp)

16 grey levels (4 bpp) 8 grey levels (3 bpp) (^) 4 grey levels (2 bpp) 2 grey levels (1 bpp)

256 grey levels (8 bits per pixel)

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Saturation & Noise

Images taken from Gonzalez & Woods, Digital Image Processing (2002) Docsity.com

Resolution: How Much Is Enough? (cont…)

  • The picture on the right is fine for counting the number of cars, but not for reading the number plate

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