Digital Signal Processing Reference
In-Depth Information
I P BBB PB BBPBB B I
Order coded and transmitted
152349 67813101112 14
Figure 14.4. Video frame sequencing
example.
Group of pictures
14.4 Compressing I-frames
I-frames are compressed in very similar fashion to the JPEG
techniques covered in the last chapter. The DCT is used to
transform pixel blocks into the frequency domain, after which
quantization and entropy coding is performed. I-frames do not
use information in any other video frame, therefore an I-frame is
compressed and decompressed independently from other
frames. Both the luminance and chrominance are compressed,
separately. Since the 4:2:0 format is used, the chrominance will
have only ΒΌ of the macrocells compared to the luminance. The
quantization table (14.1) used is given below. Once more, notice
how larger amounts of quantization are used for higher
Luminance and Chrominance Quantization Table
8
16
19
22
26
27
29
34
16
16
22
24
27
29
34
37
19
22
26
27
29
34
34
38
22
22
26
27
29
34
37
40
22
26
27
29
32
35
40
48
26
27
29
32
35
40
48
58
26
27
29
34
38
46
56
69
27
29
35
38
46
56
69
83
