Programming Assignment 1

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Programming Assignment 1

• CS308 Data Structures

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Goals

• Familiarize yourself with reading images from a
  file.
• Familiarize yourself with writing images to a
  file.
• Familiarize yourself with displaying/printing
  images.
• Improve your skills with manipulating arrays.
• Improve your understanding of constructors,
  destructors, and copy-constructors.
• Improve your skills with operator overloading.
• Learn to document and describe your programs.

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Image Datatype Functions

• Read an image from a file
• Save an image to a file.
• Get the info of an image.
• Set the value of a pixel.
• Get the value of a pixel.
• Extract a region of interest (ROI) from an image.
• Compute the mean gray-level value of an image.
• Enlarge an image by some factor s
• Shrink an image by sine factor s
• Reflect an image in the horizontal or vertical
  derections.

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Image Type Functions (contd)

• Translate an image by some amount t
• Rotate an image by some angle theta.
• Compute the sum of two images.
• Compute the difference of two images.
• Compute the negative of an image.

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Image Type Specification

• class Image
• public
• constructor //default - no parameters
• constructor //with parameters
• copy_constructor
• operator //overload assignment
• getImageInfo
• getPixelVal
• setPixelVal
• inBounds
• getSubImage
• meanGray
• enlargeImage

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Image Type Specification (contd)

• 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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readImage(fileName, image)

• 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.
• Not a member function

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writeImage(fileName, image)

• Writes out an image to a file in PGM format.
• Not a member function

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getImageInfo(noRows, noCols, maxVal)

• It returns the height (no of rows) and width (no
  of columns) of the image.
• Also, it returns the max gray-level value allowed
  (i.e.,255)
• These values should be returned using call by
  reference

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int getPixelVal(r, c)

• 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)

• 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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bool inBounds(r, c)

• Returns true if the pixel (r, c) is inside the
  image..

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

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

newImage.getSubimage( xxx )
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int meanGray()

• Computes the average gray-level value of an
  image.
• Returns the value as int (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.

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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 others.
• Most easily implemented by iterating over pixels
  of the output image and computing the coordinates
  of the corresponding input image pixel.

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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 sum of two given images.
• It is used to combine the information in two
  images.
• You can implement a simple image morphing
  algorithm !

formula


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operator- (image subtraction)

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

-

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negateImage()

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

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translateImage(t, oldImage)

• Translates the input image by some amount t.
• The translation process is performed with the
  following equations
• 
  32 x 32 translation

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rotateImage(theta, oldImage)

• Rotates the input image by some angle theta.
• The rotation process requires the use of the
  following equations

thetagt0 counter-clockwise about (0,0)
-45 degrees rotation (about the center of
the image)
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rotateImage(contd)

• Equations to rotate an image about its center
  
• Practical problems
• consider rotating pixel (0,100) by 90 degrees
• consider rotating pixel (50,0) by 35 degrees

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rotateImage(contd)

• Possible solutions
• ignore pixels whose coordinates fall outside the
  range.
• find nearest neighbors to and
• The rotated image can contain numerous holes
  where no value was computed for a pixel !!
• original
  rotated

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Questions accompanying the assignments

• Each assignment contains a number of questions
  that you must answer.
• These questions are worth 10 of the assignment
  grade.
• Answering these questions does not require prior
  knowledge of image processing.
• Your are expected to spend some time thinking
  about these questions.
• Reasonable answers will receive full points
• Interesting ideas which are implemented and
  demonstrated will get extra credit !!

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Useful Tips

• Learn how to use the debugger
• Very important for debugging your programs
  efficiently !
• There is information in the courses webpage
• Learn how to use makefiles
• Very useful when your application is split over
  many files.
• There is information in the courses webpage.