Programming Assignment 1

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Programming Assignment 1

• CS302 Data Structures

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Goals

• Improve your skills with manipulating dynamic
  arrays.
• Improve your understanding of constructors,
  destructors, and copy-constructors.
• Improve your skills with operator overloading.
• Familiarize yourself with reading/writing images
  from/to a file.
• Familiarize yourself with image processing.
• Improve your skills with documenting and
  describing your programs.

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Implementation

• You should implement
• image.h (class specification)
• image.cpp (class implementation)
• driver.cpp (application or client)

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image.h

• class Image
• public
• constructor //parameter less
• constructor //with parameters
• copy_constructor
• operator
• getImageInfo
• getPixelVal
• setPixelVal
• getSubImage
• meanGray

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image.h (contd)

• enlargeImage
• shrinkImage
• reflectImage
• translateImage
• rotateImage
• operator
• operator-
• negateImage
• private
• int N //no of rows
• int M //no of columns
• int Q //no of gray-level values
• int pixelVal

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First ...

• Carefully implement the following functions
• constructor
• destructor
• copy-constructor
• assignment

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readImage(fileName, image)(client function has
been provided)

• Reads in an image in PGM format from a file.
• A NOT-PGM exception should be raised if the
  image is not in PGM format.

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writeImage(fileName, image) (client function
has been provided)

• Writes out an image to a file in PGM format.

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getImageInfo(noRows, noCols, maxVal) (member
function has been provided)

• Returns
• the height ( of rows)
• width ( of columns) of the image
• the max gray-level value allowed (i.e., 255 for
  8-bit images)
• These values are returned using call by
  reference.

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int getPixelVal(r, c) (member function has
been provided)

• Returns the pixel value at (r, c) location.
• An OUT-OF-BOUNDS exception should be raised if
  (r,c) falls outside the image.

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setPixelVal(r, c, value) (member function has
been provided)

• Sets the pixel value at location (r, c) to value.
• An OUT-OF-BOUNDS exception should be raised if
  (r,c) falls outside the image.

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getSubImage(Ulr, Ulc, LRr, LRc, oldImage)

• It crops a rectangular subimage from the input
  image.
• The subimage can be defined by the coordinates of
  its upper-left (UL) and lower-right (LR) corners.
• Useful for limiting the extent of image
  processing operations to some small part of the
  image.

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int meanGray()

• Computes the average gray-level value of an
  image.
• Returns the value as int (i.e., truncate the
  result)

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enlargeImage(s, oldImage)

• Enlarges the input image by some integer factor
  s
• It is useful for magnifying small details in an
  image.

2 times the original size
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enlargeImage (contd)

• Replicate pixels such that each pixel in the
  input image becomes an s x s block of identical
  pixels in the output image.
• Most easily implemented by iterating over pixels
  of the output image and computing the coordinates
  of the corresponding input image pixel.

Example s 2
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shrinkImage(s, oldImage)

• Shrinks the input image by some integer factor s
• It is useful, for example, for reducing a large
  image in size so it fits on the screen.

1/2 times the original size
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shrinkImage (contd)

• Sample every s-th pixel in the horizontal and
  vertical dimensions and ignore the other.
• Most easily implemented by iterating over pixels
  of the output image and computing the coordinates
  of the corresponding input image pixel.

Example s 2
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reflectImage(flag, oldImage)

• Reflects the input image along the horizontal or
  vertical directions.

vertical reflection
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reflectImage (contd)

• Reflection along either direction can be
  performed by simply reversing the order of pixels
  in the rows or columns of the image

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operator (image addition)

• Computes the weighted sum of two images.
• You can use it for simple image morphing !

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operator- (image subtraction)

• Computes the difference of two given images.
• Useful for change detection.
• Compute absolute difference

-

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negateImage()

• Computes the negative of an image.
• This can be done using the following
  transformation

negative
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translateImage(t, oldImage)

• Translates the pixel locations by some amount t.
• Translation can be performed using the equations
  
• 
  
• 
  32 x 32
  translation

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rotateImage(theta, oldImage)

• Rotates the input image by some angle theta about
  (0,0).
• Rotation uses the following equations

if theta gt 0 counter- clockwise about (0,0)
if theta lt 0 clockwise about (0,0)
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rotateImage (contd)

• Equations to rotate an image about any point
  

-45 degrees rotation (about the center of
the image)
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rotateImage (contd)

• Practical problems
• consider rotating pixel (0,100) by 90 degrees
• consider rotating pixel (50,0) by 35 degrees

Ignore pixels whose coordinates fall outside the
range. Find nearest neighbors to and
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rotateImage(contd)

• Serious problem the rotated image could contain
  numerous holes where no value was computed for
  a pixel !!
• original rotated

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Extra Credit

• Usually, each assignment will contain a number of
  extra credit questions answering the extra
  credit questions is optional.
• Your are expected to spend some time thinking
  about each question and provide a reasonable
  answer.
• Reasonable ideas, which have been implemented and
  demonstrated to the TA, will get extra credit !!

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Useful Tips

• Learn how to use a debugger
• Very important for debugging your programs
  efficiently!
• Learn how to use makefiles (especially if you use
  Linux/Unix)
• Very useful when your application is split over
  many files.