Computer Graphics Exercise 1 Halftoning and Color Transfer Due date:

Part 1 Halftoning

General Description The purpose of this part of the exercise is to generate half tone images with two techniques: i.Ordered Dithering. i.Ordered Dithering. ii.Error Distribution. ii.Error Distribution.

Original Image

Ordered Dithering

Error Diffusion Propagate the error to the Four surrounding neighbours

Program Usage The program should be named “ halftoning.exe ”. The programs gets from the command line TWO parameters: 1. Option –d or –e 2. Input filename

Program Usage The program generates one output image dither_ ( -d option) dither_ ( -d option) errdiff_ ( -e option) errdiff_ ( -e option)

Part 2 Color Transfer

General Description  The purpose of this part is to implement a simple algorithm that transfers the colors of one image onto another image.

Example Colors Result:

The algorithm  You will find an affine mapping (Matrix + translation) between the color spaces of the two images.  For every pixel i of the first image, you take its color p i = (r i, g i, b i ), and apply the mapping M.  You obtain the new color for pixel i :

In detail R B G R B G How to find a good mapping?

Mapping by PCA R B G R B G  Find the axes by PCA  Compute the oriented bounding boxes  Define M as the affine mapping between those boxes!

Program Usage The program should be named “ ColorTransfer.exe ”. The programs gets from the command line TWO parameters: 1. First input filename (the one to map the colors onto) 2. Second input filename (the one to take the colors from)

Program Usage The program generates one output image res_ res_

General Guidelines

Important Remarks  You should write the programs in C or C++.  Document your program thoroughly.  In this assignment there is no need to open a window or use OpenGL in any way.

Important Remarks  The work can be done in pairs.  Submit your work on diskettes (or CD’s). Hardcopy of the documentation.  Points will be rewarded for nice and original images.

More Important Remarks  Don't forget to check the number of parameters that your program receives.  Don't forget to check memory allocations, if they succeeded or failed.  Pay attention to the difference between bytes, int’s and float’s (Rounding error).  Pay attention to the borders of the image.

A Little Help  IrfanView – An image viewer, editor.  FreeImage – A open source library for working with images.  NewMat10 – matrix and linear algebra library  See the links on the exercise webpage