1. Yu-Chi Lai Mohamed Eldawy
Project 1 Help Section
Yu-Chi Lai
Mohamed Eldawy
11/13/2018
© University of Wisconsin, CS559 Fall 2006

2. © University of Wisconsin, CS559 Fall 2006
Topics
Color Dithering
Warping
Impressionist
Questions
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© University of Wisconsin, CS559 Fall 2006

3. Transformation from One Image to Another
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© University of Wisconsin, CS559 Fall 2006

4. Dithering with Floyd-Steinberg
Procedures for black and white
Turn color into grayscale: I=0.299R+0.587G+0.114B
Fill in the pixel with either black or white depends on the luminance of the current pixel
Diffuse the error (luminance difference between filled value and current value) to the adjacent unprocessed pixels
Zigzag until we reach the end can improve the result e
7/16
3/16
5/16
1/16
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© University of Wisconsin, CS559 Fall 2006

5. © University of Wisconsin, CS559 Fall 2006
Dithering with Color
Difference between black-white and color dithering:
Choose the closest color from the palette for the current pixel
Diffuse the error (color difference in r, g, b) to the adjacent unprocessed pixels
11/13/2018
© University of Wisconsin, CS559 Fall 2006

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Result
(149, 91, 110)(176, 116, 137)
(17, 11,15) (63, 47, 69)
(93, 75, 112)(47, 62, 24)
(76, 90,55)(190, 212, 115)
(160, 176, 87)(116, 120, 87)
(245, 246, 225)(148, 146, 130)
(200, 195, 180)(36, 32, 27)
(87, 54, 45)(121, 72, 72)
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7. © University of Wisconsin, CS559 Fall 2006
Image Warping
A mapping between pixel locations
No color changes
Examples
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Some Examples
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Challenges (1)
Direction of transform
for(int i = 0 ; i < wid ; i ++)
for(int j = 0 ; j < hei ; j ++) {
(i’,j’)= location of (i,j) in the destination
result(i’,j’) = source(i,j) } OR
(i’,j’)= location where (i,j) comes from result(i,j) = source(i’,j’)
Forward
Backward
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10. © University of Wisconsin, CS559 Fall 2006
Challenges (2)
for(int i = 0 ; i < wid ; i ++)
for(int j = 0 ; j < hei ; j ++) {
(i’,j’)= location where (i,j) comes from result(i,j) = source(i’,j’) }
Choosing a sampling method
Nearest neighbor
Bilinear
Gaussian
Could be non-integer
11/13/2018
© University of Wisconsin, CS559 Fall 2006

11. © University of Wisconsin, CS559 Fall 2006
Challenges (3)
This is not really a one to one mapping
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12. © University of Wisconsin, CS559 Fall 2006
Coding Hints
A function that computes the mapping makes changing functions much easier
void transform(int x,int y, float& x2, float& y2)
A sampling function makes it easier to change sampling method
RGBTriple sample(int samplingMethod, float x,float y)
Don’t forget to handle the case of coordinates outside image
Can also be used in your resizing code
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Impressionist
Transform an image like a photo or a poster to some human artistic styles.
From observation of human drawings, we must determine
Do it manually or automatically
Where to draw
What color should we use
What size and shape of pens should we use
What order should we place our draws
What direction should we draw
11/13/2018
© University of Wisconsin, CS559 Fall 2006

14. Impressionist (Automatic)
Easiest way to think about it is block by block
Too mechanic
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Detailed (1)
To make it look nature, we can do
Choose the drawing points randomly
Random choose the size of the pen and size of the strokes
Perturbation of the choosing color.
Orientation of the strokes
Choose a special shape for the pen used such as square, circle, eclipse, or others.
Choose how to solve overlap problem
Make sure that the entire pictures has been covered
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Detailed (2)
Solve the overlap problem
Blending like watercolor drawing
Overwrite like oil painting
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Code Hint
For reusing your code, you can have a function to place a draw on a position with your own designed shape, size and so on.
For example, I used this function
void PlaceDraw(BrushShape, Position, Size, FlagFor BlendingMethod)
BrushShape: an array to indicate the brush property e.g. circle, square
Position: two float numbers to indicate where to place the draw
Size: a float number, the size of the draw
FlagForBlendingMethod: integer to indicate overlap, blending, or other method
11/13/2018
© University of Wisconsin, CS559 Fall 2006

18. Advance: Layer Drawing
When observing how human draw.
Put a background color on.
Draw big regions
Draw small regions in each big region.
Draw the detail on each small region.
Pyramid Method
Decompose a picture into image pyramid (When implementing it, we use different size of filtering kernel
Place draws according to the information in each layer with different size of brush.
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© University of Wisconsin, CS559 Fall 2006

19. Questions about Project 1 ?
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© University of Wisconsin, CS559 Fall 2006