W99681CF Datasheet, PDF (26/78 Pages) Winbond – JPEG USB Dual Mode Camera Chip

W99681CF
7.3.3 Huffman Encoding
After quantization, the quantized coefficients are converted to the zig-zag sequence for Huffman
encoding. The DC coefficients are coded differently from the AC coefficients. The value that should be
encoded is the difference (DIFF) between the quantized DC coefficient of the current block (DC_i which
is also designated as Sq₀₀) and that of the previous block of the same component (PRED):
DIFF = DCi − PRED
At the beginning of the scan and at the beginning of each restart interval, the prediction for the DC
coefficient prediction is initialized to 0.
For the AC coefficient encoding, since many AC coefficients are zero, runs of zeros are identified and
coded efficiently. In addition, if the remaining coefficients in the zig-zag sequence order are all zero, this
is coded explicitly as an end-of-block (EOB).
The W99681CF Huffman encoder employs two DC and two AC Huffman tables within one scan for
luminance and chrominance components.
7.3.4 JPEG Encoding Order
The W99681CF JPEG encoder supports two non-interleaved encoding orders shown in Figure 7.2:
• YUV4:2:2 non-interleaved encoding order
• YUV4:2:0 non-interleaved encoding order
Y₁ Y₂ Y₃ Y₄
Y_n
Y₁ Y₂
Y₃ Y₄
Y_n
U₁ U₂ U₃
U_n/2
V₁ V₂ V₃
Y₁, Y₂, ...Y_n U₁, U₂, ...U_n/2 V₁, V₂, ...V_n/2
Scan 1
Scan 2
Scan 3
YUV4:2:2 Non-interleaved Encoding Order
V_n/2
U₁ U₂
U_n/4
V₁ V₂
Y₁, Y₂, ...Y_n U₁, U₂, ...U_n/4 V₁, V₂, ...V_n/4
Scan 1
Scan 2
Scan 3
YUV4:2:0 Non-interleaved Encoding Order
V_n/4
Figure 7.2 JPEG Encoding Order
- 26 -