1. imshow function uint8 data type (0-255) double data type (0.0-1.0)
imshow(x) is ok
double data type ( )
Wrong example:
c=imread('caribou.tif');
cd=double(c);
imshow(c), figure, imshow(cd)
Right method:
imshow(cd/255) 或 imshow(cd, [])

2. Bit planes Bit plane 0 Bit plane 1 Show multiple images in a figure
c0=mod(cd, 2);
Bit plane 1
c1=mod(floor(cd/2), 2);
Show multiple images in a figure
figure, subplot(1,2,1), imshow(c0);
subplot(1,2,2), imshow(c1);
Exercise#1: Show bit plane 0 to 7 in a figure (3 by 3 arrangement)

3. Quantization 量化 Reduce the number of gray levels
Example: 256 levels -> 4 levels
f=floor(double(cd)/64);
q=uint8(f*64); % scale it
Exercise#2: quantize to 2, 8, 16, 64 levels
Original values
Output values
0-63
64-127 1 2 3

4. Halftoning and dithering
Halftoning(半色調): representing an image with only two tones
Simply quantization cause false contours
Dithering(混色): adding random values to the image before quantization
D=[0 128; ];
r=repmat(D,128,128);
x=cd>r; imshow(x);

5. Idea of dithering
Exercise#3: dithering using

6. Arithmetic operations
Image addition and subtraction
a=uint8(double(c)+128);
a1=imsubtract(c, 128);

7. Lookup tables (LUT) Example: MATLAB code: T=uint8(floor((0:255)/2));
ct=T(c); % what’s wrong …
index
LUT …

8. Piecewise linear function using LUT
255
t1=0.6667*[0:96];
t2=2*[97:160]-128;
t3=0.6632*[161:255]+85.89;
T2=uint8(floor([t1 t2 t3]));
cT2=T2(cd+1);
192 64 96
160
255

9. Exercise#4
For the tire image, build a LUT that performs gamma transform
s=cr0.5