ECE 418 C++ Library Documentation

Introduction

In this course you will be performing different manipulations on images. This library was written to remove some of the more tedius and error-prone aspects from the labs.

The main structure in this library is the Image class and some variations, the ComplexImage and ComplexFFTImage.

The Image class is for images whose pixels are integer-valued, from 0 through 255.

The ComplexImage class (used in Lab 2) is for images whose pixels have complex floating-point values. the ComplexFFTImage class (used in Lab 3) is the same as ComplexImage except it has built-in routines to Fourier-transform and untransform the image.

In addition to using the course-specific structures, you will also use the Complex class, which is an instance of the C++ Standard Template Library's built-in support for complex numbers.

The following documentation will give you enough information to complete all of the labs in this course. You are encouraged to look at the source code of the library.

Loading and saving images

• The following line will create an Image called myImage:
  Image myImage;

• To load the contents of inPicture.png into myImage type:
  myImage.LoadPng ("inPicture.png");

• To save the contents of myImage into outPicture.png type:
  myImage.SavePng ("outPicture.png");

Modifying an image

• To resize myImage to be x by y pixels, type:
  myImage.Resize (x, y);

• To get the grey value of the pixel at (x,y) and store it in z, type:
  z = myImage.Pixel (x, y);
  

• To set the grey value of the pixel at (x,y) to z, type:
  myImage.Pixel (x, y) = z;

• Note that for setting and getting pixel values, if myImage is a ComplexImage or ComplexFFTImage then z must be of type Complex.

Complex numbers

The STL that comes with C++ includes support for complex variables. In this class, the Complex type represents floating-point complex variables. Here are some of their more useful features:

• To create a complex variable z initialized to zero, type:
  Complex z;
  

• To create a complex variable w initialized to a+bi, type:
  Complex w (a, b);

• To access the real or complex parts of z, type:
  z.real () or z.imag ()
  

  Note that you can NOT write to these, typing z.real () = 3 will not compile. If you want to set z to a + bi, you will have to type:
  z = Complex (a, b);

• To set x to the magnitude of z, type:
  x = abs(z);

Note that in many cases, the double type and Complex types are compatible. That is you can add, multiply, divide, and assign Complex variables with double variables. Therefore, the following code block is valid and will do what you expect it to do.