Game Development Reference
In-Depth Information
Table 7.2 The classification rules and pixel categories
Category
Condition
Offset range
1
c
<
a && c
<
b
1
offset
6
2
( c
<
a && c
==
b )
( c
==
a && c
<
b )
0
offset
1
3
( c > a && c == b ) ( c == a && c > b )
1 offset 0
4
c
>
a && c
>
b
6
offset
1
0
None of the above
None
Fig. 7.7 Positive offsets for EO categories 1 and 2 and negative offsets for EO categories 3 and 4
result in smoothing
values and original pixel values. The offset and the index of classification pattern are
transmitted to a decoder.
To further reduce complexity, the range of offset value for each category is also
limited as shown in Table 7.2 . For category 1 and 4 associated with a local valley
and a local peak along the selected 1D pattern, the range of offset is set to [
1,
6] and [
6, 1], respectively. For category 2 and 3 associated with concave and
convex corners along the selected 1D pattern, the range of offset is set to [0, 1] and
[
1, 0] respectively. If the current sample does not belong to EO categories 1-4, it is
classified as category 0, and EO is not applied. The meaning of the edge offset signs is
illustrated in Fig. 7.7 . Positive offsets for categories 1 and 2 result in smoothing since
local valleys and concave corners become smoother, while negative offset results
sharpening. The same meaning is also for categories 3 and 4. Based on the priori
knowledge of image smoothness in statistics, the range of EO prefers to smooth
inflection in images.
Band offset mode classifies the pixels into 32 categories by equally dividing the
pixel range. For 8-bit pixels ranging from 0 to 255, the width of a band is 8, and pixel
values from 8 k to 8 k
7 belong to band k , where k ranges from 0 to 31. The range of
band offset for all the bands is [
+
7, 7]. Although one offset is derived by an encoder
 
 
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