# Confusion on motion estimation block diagram-MPEG video compression-:

• Comp Sci
• shivajikobardan
In summary, the block matching algorithm searches the blocks in the n-1 frame, and if it finds a close match to the current block in the n frame, it sends an instruction to the receiver to use that already received block from n-1.
shivajikobardan
Homework Statement
block matching algorithm confusion
Relevant Equations
none

My doubts are as follows-:

-> Why frame n is not segmented to blocks?

-> Why no inputs from (n-1) side for block matching?
-> What do we do in prediction error coding?

Source-: https://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/AV0506/s0561282.pdf

I have read this many times but that didn’t help to clear my doubts.

This video. This confused the hell out of me.

shivajikobardan said:
Homework Statement:: block matching algorithm confusion
Relevant Equations:: none

-> Why frame n is not segmented to blocks?
It is.
The poorly worded description you have only implies the block operation, for instance by showing it in the figure as "Block Matching." Later text also describes operations that can only be done on blocks.

-> Why no inputs from (n-1) side for block matching?
There is.
Again the figure shows Block Matching output for the two frames feeding the "Prediction Error Coding" operation.

Both of the above are explained (sort of) on pgs 3 and 4 of the document you linked.

-> What do we do in prediction error coding?
The Block Matching searches the blocks in the n-1 frame, and if it finds a close match to the current block in the n frame, it sends an instruction to the receiver to use that already received block from n-1.
However that n-1 block is not always an exact match due to image motion between frames.
The Prediction Error Coding then sends a 'Correction' factor that the receiver applies to n-1 frame to account for any motion that may have occurred between frames.

Note that this requires the receiver to keep a copy of the reference (previous) frame for comparison.

Hope this helps!

Cheers,
Tom

p.s. By the way, I found the video useless, I could not understand the accent of the presenter.

sysprog and berkeman
Tom.G said:
It is.
The poorly worded description you have only implies the block operation, for instance by showing it in the figure as "Block Matching." Later text also describes operations that can only be done on blocks.There is.
Again the figure shows Block Matching output for the two frames feeding the "Prediction Error Coding" operation.

Both of the above are explained (sort of) on pgs 3 and 4 of the document you linked.The Block Matching searches the blocks in the n-1 frame, and if it finds a close match to the current block in the n frame, it sends an instruction to the receiver to use that already received block from n-1.
However that n-1 block is not always an exact match due to image motion between frames.
The Prediction Error Coding then sends a 'Correction' factor that the receiver applies to n-1 frame to account for any motion that may have occurred between frames.

Note that this requires the receiver to keep a copy of the reference (previous) frame for comparison.

Hope this helps!

Cheers,
Tom

p.s. By the way, I found the video useless, I could not understand the accent of the presenter.
Hmm you're telling it includes everything..but it isn't included in figure I'm confused....can you explain 1 round of this flowchart in small brief? I'm really confused..btw what happens in block matching?

Very general hint: whenever I find a document on some technology confusing I google other sources to do a cross check. The more, the better.

Tom.G and sysprog

## 1. What is the purpose of the motion estimation block in MPEG video compression?

The motion estimation block is responsible for identifying and tracking the movement of objects in a video sequence. This information is used to reduce redundancy in the video data and improve compression efficiency.

## 2. How does the motion estimation block work?

The motion estimation block uses a variety of algorithms to compare blocks of pixels in different frames of a video. It then calculates the motion vectors, which indicate the direction and distance of the movement. These motion vectors are used to predict the location of objects in subsequent frames, reducing the amount of data that needs to be encoded.

## 3. What is the difference between motion estimation and motion compensation?

Motion estimation is the process of identifying and tracking motion in a video sequence, while motion compensation is the process of using this information to predict the location of objects in subsequent frames. Motion estimation is a crucial step in the motion compensation process.

## 4. Are there different types of motion estimation algorithms?

Yes, there are several types of motion estimation algorithms, including block matching, gradient-based methods, and optical flow. Each algorithm has its own advantages and limitations, and the choice of algorithm often depends on the characteristics of the video being compressed.

## 5. What are the benefits of using motion estimation in video compression?

Motion estimation helps to reduce the amount of data that needs to be encoded, resulting in smaller file sizes and improved video quality. It also allows for more efficient compression of videos with a lot of motion, such as sports or action scenes.

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