Programming Assignment 1

Programming Assignment 1 CS302 Data Structures

Goals • Improve your skills with manipulating dynamicarrays. • 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.

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

image.h • class Image { • public: • constructor//parameter less • constructor//with parameters • copy_constructor • operator= • getImageInfo • getPixelVal • setPixelVal • getSubImage • meanGray

image.h (cont’d) • 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; • };

First ... • Carefully implement the following functions: • constructor • destructor • copy-constructor • assignment

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.

writeImage(fileName, image)(client function – has been provided) • Writes out an image to a file in PGM format.

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.

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.

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.

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.

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

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

enlargeImage (cont’d) • 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

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

shrinkImage (cont’d) • 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

reflectImage(flag, oldImage) • Reflects the input image along the horizontal or vertical directions. vertical reflection

reflectImage (cont’d) • Reflection along either direction can be performed by simply reversing the order of pixels in the rows or columns of the image

operator+ (image addition) • Computes the weighted sum of two images. • You can use it for simple image morphing ! + =

operator- (image subtraction) • Computes the difference of two given images. • Useful for change detection. • Compute absolute difference: - =

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

translateImage(t, oldImage) • Translates the pixel locations by some amount t. • Translation can be performed using the equations: • 32 x 32 translation

rotateImage(theta, oldImage) • Rotates the input image by some angle theta about (0,0). • Rotation uses the following equations: if theta > 0: counter- clockwise about (0,0) if theta < 0: clockwise about (0,0)

rotateImage (cont’d) • Equations to rotate an image about any point : -45 degrees rotation (about the center of the image)

rotateImage (cont’d) • 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

rotateImage(cont’d) • Serious problem: the rotated image could contain numerous “holes” where no value was computed for a pixel !! • original rotated

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 !!

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.

Programming Assignment 1