![](https://csdnimg.cn/release/download_crawler_static/12471332/bg3.jpg)
Q. M. Yi et al.
10.4236/jcc.2018.64005 55 Journal of Computer and Communications
where,
and
denote the basic threshold of adaptive back-
ground luminance and texture masking;
C
lt
represents the overlapping part of
two kinds of effects, and it is used to adjust the two factors. The larger the
C
lt
value is, the stronger superposition between the adaptive background luminance
and texture masking is. When
C
lt
is 1, the superposition effect between the two
factors is the greatest; when
C
lt
is 0, there is no superposition effect between the
two effects. In fact, the superposition is between the maximum and the mini-
mum, where
C
lt
is equal to 0.3.
Figure 1 shows the curve of the background luminance and the visual thre-
shold obtained from the experimental results. It simulates the background lu-
minance model and shows the distortion threshold that the human eye can tole-
rate under a certain background luminance.
can be determined according to the visual threshold curve in Figure
1.
( )
( )
( )
( )
( )
,
17 1 3 , , 127
127
,
3
, 127 3, others
128
Y
Y
l
Y
I xy
I xy
T xy
I xy
−+ ≤
=
−+
(2)
where
is the average background luminance value.
Due to the characteristics of HVS itself, distortion that occurs in plain and
edge areas is more noticeable than texture areas. In order to estimate the JND
threshold more accurately, it is necessary to distinguish the edge and non-edge
regions. Therefore, considering the edge information, the calculation method of
the texture masking threshold
is:
( ) ( ) ( )
, ,,
t
T xyGxy xyW
θθ
β
=
(3)
where
β
is the control parameter and its value is set as 0.117.
donates
the maximal weighted average of gradients around the pixel at (
x
,
y
);
is an edge-related weights of the pixel at (
x
,
y
), and its corresponding matrix
is detected by the Gaussian low-pass filter.
Figure 1. Background luminance and visual threshold.