**ISO/IEC 10918-1 : 1993(E)**

c

b

x

a

TISO1680-93/d106

**Figure H.1 Relationship between sample and prediction samples**

Figure H.1 [D106] = 4.5 cm = 176 %

Define Px to be the prediction and Ra, Rb, and Rc to be the reconstructed samples immediately to the left, immediately

above, and diagonally to the left of the current sample. The allowed predictors, one of which is selected in the scan

header, are listed in Table H.1.

**Table H.1 Predictors for lossless coding**

Selection-value

Prediction

0

No prediction (See Annex J)

1

Px

=

Ra

2

Px

=

Rb

3

Px

=

Rc

4

Px

=

Ra

+

Rb Rc

5

Px

=

Ra

+

((Rb Rc)/2)

a)

6

Px

=

Rb

+

((Ra Rc)/2)

a)

7

Px

=

(Ra

+

Rb)/2

a)

Shift right arithmetic operation

Selection-value 0 shall only be used for differential coding in the hierarchical mode of operation. Selections 1, 2 and 3 are

one-dimensional predictors and selections 4, 5, 6, and 7 are two-dimensional predictors.

The one-dimensional horizontal predictor (prediction sample Ra) is used for the first line of samples at the start of the scan

and at the beginning of each restart interval. The selected predictor is used for all other lines. The sample from the line

above (prediction sample Rb) is used at the start of each line, except for the first line. At the beginning of the first line and

at the beginning of each restart interval the prediction value of 2

P 1

is used, where P is the input precision.

If the point transformation parameter (see A.4) is non-zero, the prediction value at the beginning of the first lines and the

beginning of each restart interval is 2

P Pt 1

, where Pt is the value of the point transformation parameter.

Each prediction is calculated with full integer arithmetic precision, and without clamping of either underflow or overflow

beyond the input precision bounds. For example, if Ra and Rb are both 16-bit integers, the sum is a 17-bit integer. After

dividing the sum by 2 (predictor 7), the prediction is a 16-bit integer.

**CCITT Rec. T.81 (1992 E)**

**133**