1. COMPLEXITY VARYING INTRA PREDICTION IN H.264
by Leonid Ostrovsky
Supervisors:
Dr. Ofer Hadar, Mr. Evgeny Kaminsky

2. H.264 overview (a.k.a. MPEG 4 Part 10) Advanced codec
Superior to previous standards:
Relies on multiple frames in GOP
Uses both 4x4 and 16x16 macroblocks
Up to quarter pixel precise
Uses prediction on the basis of edges of neighboring macroblocks (instead of DC)

3. H.264 overview: Compression
Figure 1:GOP (Group Of Pictures)
GOP (Why do we need this?)
I-frames
B- and P-frames
Spatial and temporal redundancy
We’re able not to encode the whole picture

4. H.264 overview: Compression
Figure 2: Encoding process
We’re able to encode just the residue
Inter- and Intra- prediction

5. H.264 overview: Intra-Prediction
Reminder: What is it?
How do we predict?
Cost function
J = Distortion + λmode *Rate
Prediction modes
Figure 3: 4x4 modes
Figure 4: 16x16 modes

6. H.264 overview: Intra-Prediction
Problem: Too many modes to check! (592 for each macroblock)
Quite problematic for embedded sys.
What if:
We could cut this number down…
…by finding the most probable modes to be chosen?
This leaves some open questions:
How many modes?
Which modes ?

7. The method Sobel filter
Figure 5: Sobel filter
Now we can see which mode is the most probable one
However, we cannot use static allocation (will greatly influence the buffering)

8. The method
We must cut down the modes in such way that more complex macroblocks will be more compressed
It is done in a relative fashion…
…i.e. the most complex block will get 9 modes and the least complex one will get 1
By this we ensure lesser buffering

9. The method The final goal is:
To achieve a situation in which by giving a certain time limit …
…the CODEC will allocate modes in such way that computational complexity will not cross that limit
By this we can assure that embedded systems with low energy resources could set the limit lower than usual ensuring by that low waste of energy

10. The outcome so far There is a fully working Sobel filter
There is a dynamic mode allocating mechanism in 4x4 block mode
Actually, even though that wasn’t my goal I already have CODEC that works more effective than the original standard.
Let’s see some statistics:

11. Results:

12. Results:

13. Results: Also: average number of modes per macroblock is : 1.9868
Variance of rate per frame in my algorithm is when in 2-mode state , for instance, is 49325
i.e. lower buffering

14. Future goals
To extend same algorithm to 16x16 mode (and if I get to it, to chroma component)
To develop a new cost function from the following format:
J = Distortion +λMODE *Rate
As you can see it’s the same as the standard function. However this one will also include time limit
To test and check the whole algorithm