Full text: Proceedings; XXI International Congress for Photogrammetry and Remote Sensing (Part B6b)

The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B6b. Beijing 2008 
horizontal detail coefficients (LH), the vertical detail 
coefficients (HL), and the diagonal detail coefficients (HH) [10] . 
cA 
row 
*j Lo_D 
HIJD 
column 
„3' 42Ïr\ cAj,, 
column 
Hi_D "j—4a"T» \ —cD%, 
column 
*■ Lo D | 2J1 ■ 
J“~*i 2 * i U co 1 umn 
- Hi_o 4.2 if'].. . 
(a) 
£vt /*i—*£* Î 2 } 
column 
c! *>■' —*1 1 Î 2 \~ 
•c 
Lo_R 
V 
column 
* 
MI_R 
r 
co 1. umn 
■T 
Lo_R 
L 
column 
c 
HL.* 
> 
Lo R j 
H1_R 
-cA. 
——« 1 J2 
Figure 2. Diagram of 2-D WT decomposition (a) and 
reconstruction (b) 
Figure 5. Emulational image of non uniform illumination model 
We can see that approximate and detail coefficients of the even 
illumination image are almost in a plane, and the uneven 
illumination image detail coefficients are almost in a plane, 
only the extent enlarged, but the approximate coefficients is not 
in a plane at all. 
J* ¿“p J ; 
1 level WT 
LL 
HL 
LH 
HH 
Figure 3. Diagram of Single-level 2-D wavelet transform 
The attenuating illumination model represented in formula (8) 
shows that the illumination attenuates slowly from the image 
central point to the around. This means that, the illumination 
attenuating model corresponding to the low frequency part. In 
wavelet transform, the low frequency signal is correspond to the 
approximate coefficients. So it can be concluded that the 
approximate coefficients are most sensitivity to the illumination 
attenuation. While the detail coefficients correspond to the 
detail information such as image edges. 
For testing the above feature, emulational image of even 
illumination image is given in Figure 4, illumination non 
4 
uniform model accord to cos ® is given in Figure 5. After one 
level wavelet transform of these two figures, wavelet 
coefficients are shown from Figure 6 to Figure 9.
	        
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