Homework 04 Color Models and Interpolation

KTH Stockholm
EECS :: CST
Introduction to Visualization and Computer Graphics

Homework assignment No. 04

Before beginning the assignment, use git pull to get the latest version of our Inviwo repository. Run
CMake and compile once more.
Task 4.1: Color Models and Interpolation 10 P
Implement color interpolation and manipulation for different color models! The user interface allows you to choose
two colors Color A and Color B. You will interpolate between them in RGB, CMYK, and HSV. Furthermore,
you will change two dimensions of a given HSV color and obtain a slice through the HSV color model. The initial
setup and the final result can be seen in Fig. 1.
Make sure to interactively change the two input colors Color A and Color B and observe the changes. Does the
choice of color model matter when interpolating colors?
• Inviwo Workspace: File → Example Workspaces → DH2320Lab2 → ColorInterpolation.inv
• File: ...\Inviwo\modules\dh2320lab2\colorinterpolation.cpp
• Functions for color interpolation: You need to edit the functions void InterpolateInRGB(...),
void InterpolateInCMYK(...), and void InterpolateInHSV(...). They all return the interpolation result as a color in the respective color model. All these interpolation functions have three inputs:
– const ...& ColorA: color to be interpolated in the respective color model
– const ...& ColorB: color to be interpolated in the respective color model
– const float t: interpolation parameter in the range [0, 1].
• Functions for color manipulation in HSV: You need to edit the functions void ChangeValueAndSaturation(...)
and void ChangeHueAndSaturation(...). They both return a color in the HSV color model. The functions
have three inputs: a HSV color and two parameters to change this color. See the source code comments
for details.
(a) Setup (b) Result
Figure 1: Color Interpolation
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Task 4.2: Additive versus Subtractive Color Mixing 4 P
Implement additive and subtractive color mixing! The user interface allows you to select the three primary colors
in both setups. The initial setup and the final result can be seen in Fig. 2. The shown result reproduces the
images from the lecture slides, which is a good testing scenario.
• Inviwo Workspace: File → Example Workspaces → DH2320Lab2 → ColorMixing.inv
• File: ...\Inviwo\modules\dh2320lab2\colormixing.cpp
• Function for additive color mixing: You need to edit the function void AdditiveColorMixing(...)
which returns the mixed color based on the following input parameters:
– const vec3& Color1: color to be mixed
– const vec3& Color2: color to be mixed
• Function for subtractive color mixing: You need to edit the function void SubtractiveColorMixing(...)
which returns the mixed color based on the following input parameters:
– const vec3& ColorIncomingLight: color of the incoming light
– const vec3& ColorSurface: color of the surface where the light will be reflected
(a) Setup (b) Result
Figure 2: Color Mixing
Task 4.3: Chaikin’s Corner Cutting 15 P
Implement Chaikin’s corner cutting algorithm! The initial setup and the final result can be seen in Fig. 3.
• Inviwo Workspace: File → Example Workspaces → DH2320Lab2 → Chaikin.inv
• File: ...\Inviwo\modules\dh2320lab2\chaikin.cpp
• Function: You need to edit the function void Chaikin::CornerCutting(...) which takes the following
parameters:
– const std::vector<vec3& ControlPolygon: points defining the line segments to be subdivided
– const size_t MinNumDesiredPoints: minimum number of points the resulting curve should contain
– std::vector<vec3& Curve: points of the resulting curve after applying corner cutting
Task 4.4: Curve Simplification (Extra Task) 5 Extra Points
Chaikin’s Corner Cutting creates polylines with many samples. In less curved parts of the polyline, a significantly
smaller number of samples would suffice. Implement an algorithm to reduce the number of sample points while
retaining the overall shape of the curve as much as possible.
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(a) Setup (b) Result
Figure 3: Chaikin’s Corner Cutting
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