4.1.2.1.2 Encode Frame #1 at 50%
The quantized data is dequantized and subtracted from the input, yielding the remaining values to be sent (known as "DRS"). These values are quantized for the 50% progressive quality.
Details on the formulas for DRS and UpgradeQ are as specified in section 3.2.8.1.5.2, while details on the SRL encoder are as specified in section 3.2.8.1.5.
The difference in bit positions for the two progressive quality levels indicates how many bits of magnitude are sent to the client. For this particular upgrade, the LL band does not receive any new bits, and the number of bits is zero. Hence, no entries are generated for this band.
The previous value (zero or nonzero) that was sent determines whether the SRL encoder will be used or whether raw bits will be sent.
In this particular scenario, the first element of the HL band and the last element of the LH band produced a nonzero value in the previous pass. These absolute values are written as raw bits, with the appropriate number of bits for the band: the first written with four bits and the second written with two bits.
The SRL encoder first encodes an empty run-length ("10") before encoding the value -13. The sign is written as one bit ("1"); the magnitude minus one (12) is unary-encoded with 12 zeros and terminated with "1".
An empty run-length is encoded as one bit ("1") before encoding the next value (15). The sign is written as one bit ("0"); the magnitude minus one (14) is unary-encoded with 14 zeros. Because the magnitude is the maximum magnitude possible with four bits, the sequence is not terminated with a "1".
An empty run-length is encoded as one bit ("1") before encoding the next value, -3 ("1001").
Next, the SRL encoder encodes a run of two zeros. Even if those values are across two different bands, it is still considered to be a single run of zeros. Note that even if the elements were not consecutive in the bands, because elements in the middle would be encoded as raw bits, for example, or a band would be skipped due to not receiving any new bits, as far as the SRL encoder is concerned, those entries are considered consecutive.
|
|
HL |
LH |
LL |
|||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
DRS |
-2 |
-13 |
15 |
-3 |
0 |
0 |
-7 |
5 |
-3 |
1 |
3 |
1 |
3 |
0 |
|
UpgradeQ |
-2 |
-13 |
15 |
-3 |
0 |
0 |
-3 |
2 |
-1 |
0 |
0 |
0 |
0 |
0 |
|
Number of bits |
4 |
2 |
0 |
|||||||||||
|
Raw entries |
-2 |
|
|
|
|
|
|
|
|
0 |
|
|
|
|
|
SRL entries |
|
-13 |
15 |
-3 |
0 |
0 |
-3 |
2 |
-1 |
|
|
|
|
|
The raw result, broken down into elements, is:
-
0010 | 00
This results in the following byte:
-
0x20
The SRL result, broken down in run-length and unary encode, is:
-
1010000000000001 | 1000000000000000 | 11001 | 0010 | 100 | 1001 | 111
This results in the bytes:
-
0xA0 0x01 0x80 0x00 0xC9 0x49 0xE0
Zeros are added to each of these streams to complete the final byte.