# Compression video

## Motion estimation

Motion estimation is the process of determining motion vectors that describe the transformation from 2D image to another.

It is an ill-posed problem, becauses scenes are in 3D and they are projected in 2D images.

## Motion compensation

This is the difference between 2 frames.
The "reference" image is the one we are based on.
The "current" image is the one that we want to predict.

## Motion ambiguity

In regions with constant brightness, the vector flow is indeterminate.

## General methodology

One will use $\psi_1(x)$ and $\psi_2(x)$ to denote reference and current frames.
Intensity based method will be used.

## Yves Benabou's part

color space : en video, jamais RGB, toujours YUV

Pixels: aspect ratio

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