This document describes an exercise involving halftoning and color transfer techniques. For part 1, students are asked to implement ordered dithering and error diffusion to generate halftoned images from an input image. For part 2, students must find an affine mapping between the color spaces of two images to transfer colors from one image to the other. The program should take input filenames as parameters and output halftoned or color-transferred images. General guidelines and important remarks are provided on programming, documentation, and submission requirements.

1. Computer GraphicsComputer Graphics
Exercise 1Exercise 1
Halftoning and Color TransferHalftoning and Color Transfer
Due date: 20.11.05Due date: 20.11.05

2. Part 1Part 1
HalftoningHalftoning

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

4. Original ImageOriginal Image

5. Ordered DitheringOrdered Dithering

6. Error DiffusionError Diffusion
Propagate the error to the Four surrounding neighbours

7. Program UsageProgram Usage
The program should be namedThe program should be named
““halftoning.exehalftoning.exe”.”.
The programs gets from theThe programs gets from the command linecommand line
TWOTWO parameters:parameters:
1.1. OptionOption –d–d oror –e–e
2.2. Input filenameInput filename

8. Program UsageProgram Usage
The program generates one output imageThe program generates one output image
• dither_<input_name>dither_<input_name> ((-d-d option)option)
• errdiff_<input_name>errdiff_<input_name> ((-e-e option)option)

9. Part 2Part 2
Color TransferColor Transfer

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

11. ExampleExample
ColorsColors
Result:Result:

12. The algorithmThe algorithm
 You will find an affine mapping (Matrix +You will find an affine mapping (Matrix +
translation) between thetranslation) between the colorcolor spaces of the twospaces of the two
images.images.
 For every pixelFor every pixel ii of the first image, you take itsof the first image, you take its
colorcolor ppii = (= (rrii, g, gii, b, bii)), and apply the mapping M., and apply the mapping M.
 You obtain the new color for pixelYou obtain the new color for pixel ii::
( )M A= +p p t
( )i iM′ =p p

13. In detailIn detail
R
B
G
R
B
GHow to find
a good mapping?

14. Mapping by PCAMapping by PCA
R
B
G
R
B
G
 Find the axes by PCAFind the axes by PCA
 Compute the oriented bounding boxesCompute the oriented bounding boxes
 DefineDefine MM as the affine mapping between those boxes!as the affine mapping between those boxes!

15. Program UsageProgram Usage
The program should be namedThe program should be named
““ColorTransfer.exeColorTransfer.exe”.”.
The programs gets from theThe programs gets from the command linecommand line
TWOTWO parameters:parameters:
1.1. First input filename (the one to map theFirst input filename (the one to map the
colors onto)colors onto)
2.2. Second input filename (the one to takeSecond input filename (the one to take
the colors from)the colors from)

16. Program UsageProgram Usage
The program generates one output imageThe program generates one output image
res_<input_name_1>res_<input_name_1>

17. General GuidelinesGeneral Guidelines

18. Important RemarksImportant Remarks
 You should write the programs in C or C+You should write the programs in C or C+
+.+.
 Document your program thoroughly.Document your program thoroughly.
 In this assignment there isIn this assignment there is nono need toneed to
open a window or use OpenGL in anyopen a window or use OpenGL in any
way.way.

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

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

21. A Little HelpA Little Help
 IrfanView – An image viewer, editor.IrfanView – An image viewer, editor.
 FreeImage – A open source library forFreeImage – A open source library for
working with images.working with images.
 NewMat10 – matrix and linear algebraNewMat10 – matrix and linear algebra
librarylibrary
 See the links on the exercise webpageSee the links on the exercise webpage