Inter frame prediction and Cramp: Difference between pages

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{{two other uses|muscular pain|the band|the Cramps|the tool|Clamp (tool)}}

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'''Inter-frame prediction''' is a technique which takes advantage of the temporal [[correlation]] between consecutive [[frames]] in order to encode at lower [[bitrate|bitrates]]. The prediction of the current frame is made from past and/or future frames allowing a certain displacement ruled by the motion vectors. The image is divided into [[macroblock|macroblocks]] and for each one the encoder tries to find the macroblock in the reference frames that best matches it.

'''Cramps''' are unpleasant, often painful sensations caused by contraction or over shortening, usually of [[muscles]]. Cramps can be caused by cold or overexertion. Illness or poisoning can also cause cramps, particularly in the [[stomach]], which is referred to as [[colic]] if it fits particular characteristics. '''See also''' [[Delayed onset muscle soreness]].

==Causes Contextand treatment==

[[H.264]] is the future video coding standard which is going to replace the current [[MPEG-2]] video compression algorithm. [[H.264/MPEG-4 AVC]] was a joint job of [[ITU]] and [[ISO]].

H.264 is the MPEG-4(part 10) and the main scope is to code with the same quality at lower bitrates than prior standards.

{{unreferenced|date=March 2007}}

There are three basic causes of cramping. One is when you overflex the calf muscle. One is inadequate [[oxygenation]] of muscle, where excess lactic acid, produced by [[anaerobic respiration]], builds up and puts stress on the muscle. The other is lack of [[water]] or [[salt]]. Cramps from poor oxygenation can be improved by rapid deep breathing, as well as stretching the muscle. Cramps from lack of salt and water can be treated by stretching the muscle, and of course drinking water and increasing salt intake. Pounding on the muscle can increase soreness.

== Inter-frame coding enhancements with h.264/MPEG-4 AVC ==

Athletes are at greatest risk for muscle cramps, as excessive exercise can produce poor oxygenation.

This technique was already used in prior standards like MPEG-2. The key features in H.264 that allow higher compression are the following:

Muscle cramps can be treated by applying a soft massage on the cramped muscle, stretching the muscle and applying heat or cold. Heat improves superficial blood circulation and makes muscles more flexible, so some people find that heat is more soothing for muscle cramps than applying ice.

=== Flexible block divisions ===

[[Electrolyte]] disturbance may cause cramping and [[tetany]] of muscles, particularly [[hypokalemia]] (a low level of [[potassium]]) and [[hypocalcemia]] (a low level of [[calcium in biology|calcium]]). This problem can be solved by drinking electrolyte enhanced fluids, after strenuous muscle activity, and supplementing one's daily diet with a multi-vitamin, which contains potassium and calcium.

1) Luma block partitions of 16x16(MPEG2), 16x8, 8x16, 8x8 and if this last mode is used, the 8x8 partitions can be split up again in sizes as small as 4x4.

Muscle cramps may be a symptom of [[hypothyroidism]].

[[Image:Block division.jpg]]

Eating foods high in [[potassium]], such as [[Banana|bananas]], [[Potato|potatoes]], and [[Prune (fruit)|prunes]], can help prevent muscle cramps.<ref name="test1">[http://extension.osu.edu/~news/story.php?id=2470 Ohio State University Extension: News] Chow Line: Potassium-rich foods deter muscle cramps</ref>

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==Menstruation==

The frame to be encoded is divided into macroblocks or sub-macroblocks of the sizes shown in the figure. The prediction of each block would be the block of the same size found in the reference frames allowing a certain displacement and an offset. The prediction could also be a weighted prediction of several reference blocks.

{{Main|Dysmenorrhea}}

[[Menstrual cycle|Menstruation]] is also highly likely to cause cramps of varying severity in the [[abdomen]] that may radiate to the lower back and thighs. Menstrual cramps can be treated with [[ibuprofen]], stretching exercises or the application of heat through such means as warm baths or heating pads. Menstrual cramps that do not respond to self-treatment can be a symptom of [[endometriosis]] or other health problems. This kind of cramp cannot occur in male humans.

==Nocturnal leg cramps==

=== Quarter pixel accuracy ===

[[Nocturnal]] leg cramps are involuntary muscle contractions that occur in the [[Calf_muscle|calves]], [[soles]] of the [[feet]] or other muscles in the body during the night or (less commonly) while resting. The duration of nocturnal leg cramps is highly variable with cramps sometimes only lasting a few seconds and other times several minutes. Soreness in the muscles may remain for some time after the cramp ends. These cramps are more common in older populations but may happen to anyone. They can happen quite frequently in teenagers and in some cases while exercising at night. Nocturnal leg cramps can be very painful especially if dehydrated.

2) Quarter-pixel accuracy for motion compensation: (MPEG-2 enabled half-pixel accuracy at most). We can interpolate integer [[pixel|pixels]] in reference frames in order to find a better matching. When the motion vector is an integer it means that we will find the prediction directly in pixels of the reference frame. If a non-integer motion vector is chosen, we will find the prediction by interpolating in both vertical and horizontal directions and applying a filter.

The precise cause of these cramps is unclear. Potential contributing factors are believed to include low levels of certain minerals ([[magnesium]], [[potassium]], [[calcium ]] and [[sodium]]), [[dehydration]] and prolonged sitting. Less common causes include more serious conditions or use of drugs.

People report that quickly standing up and walking a few steps may shorten the duration of a cramp.

[[Image:Subpel_interpolation.jpg]]

An unrelated condition is [[restless legs syndrome]], an unpleasant sensation that is relieved by moving the leg, but which rarely includes cramping or pain.

Pixels at half-pixel positions are obtained by applying a 6-tap filter:

==Smooth muscle==

H=[1 -5 20 20 -5 1]

[[Smooth muscle]] contractions lie at the heart of the cramping (or colicky) pain of internal organs. These include the [[intestine]], [[uterus]], ureter (in [[kidney stone]] pain) and various others.

==Skeletal muscle==

For instance:

[[Skeletal muscle]]s are muscles that can be voluntarily controlled. Of the skeletal muscles, those which cramp the most often are the [[Calf_muscle|calves]], [[thighs]], and [[arches of the foot]].

b=A - 5B + 20C+20D+E

==See also==

Pixels at quarter-pixel positions are obtained by a simple bilinear prediction.

*[[Trigger points]]

*[[Side Stitch]]

==References==

=== Multiple reference picture motion compensation ===

{{reflist}}

==External links==

3) Multiple reference picture motion compensation.

* [http://www.disabled-world.com/artman/publish/what-are-cramps.shtml What are Cramps?]

Enables searching the reference in two different buffers (usually: List 0 stands for past frames, List 1 stands for future frames). Each buffer can store up to 16 pictures.

* [http://www.patient.co.uk/showdoc/40000075 Cramps at Patient UK]

* [http://www.digitalnaturopath.com/cond/C466089.html Leg cramps at night]

[[Category:Medical signs]]

[[Category:Muscular system]]

[[ar:الشد العضلي]]

[[Image:Multiple_references.jpg]]

[[de:Krampf]]

[[es:Calambre]]

The block prediction would be either a single block of a reference picture or a weighted average and offset from several reference pictures. It improves the performance in cases such as panes, cross-fade transitions or object discovering.

[[fr:Crampe]]

[[it:Crampo]]

=== Enhanced Direct and Skip macroblocks ===

[[nl:Kramp]]

[[pt:Cãibra]]

4) The Skip and Direct mode are frequently used and allow a lot of compression mainly in B-Pictures. When neither the residual error nor the motion vector is sent, we will call it Skip or Direct macroblock. Only a flag indicating that it is a Direct macroblock needs to be sent. The decoder will infer the motion vector of such macroblock from the already decoded frames. There are two techniques to do this:

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[[fi:Kramppi]]

[[sv:Kramp]]

TEMPORAL: (For bi-predictively coded areas) This is also known as Direct Mode.

[[vi:Chuột rút]]

[[zh:抽搐]]

The co-located macroblock’s motion vector in frame at t+1 is used to infer the motion of the direct macroblock at t.

The co-located macroblock’s motion vector in frame t+1 points at the t reference frame.

[[Image:Direct_skip.jpg]]

So the decoder infers the motion vectors MV1,MV2 from MV applying certain temporal weightings.

SPATIAL: (Skip Mode)

The [[decoder]] estimates the [[motion compensation|motion vector]] from neighboring blocks in the same frame. One simple criterion would be just to copy the neighboring block motion vector. These modes are commonly used in smooth areas where there is not a lot of motion. Prior standards didn't enable motion for this kind of macroblocks. This enhanced direct macroblock allows to encode constant motion sequences like slow panning very efficiently. As a drawback, the decoder will have to store the motion vectors also in the buffers.

[[Image:block_partition.jpg]]

The pink blocks are direct macroblocks

Skip Macroblocks appear very often in B-pictures

== References ==

# Software H.264: http://iphome.hhi.de/suehring/tml/download/

# T.Wiegand, G.J. Sullivan, G. Bjøntegaard, A.Luthra: ''Overview of the H.264/AVC Video Coding Standard''. IEEE Transactions on Circuits and Systems for Video Technology, Vol. 13, No. 7, July 2003

== External links ==

* [http://www.cri.ensmp.fr/classement/doc/E-260.pdf Tutorial de compresión de video MPEG-4 AVC]

* [http://www.oki.com/en/otr/200/downloads/otr-200-R14.pdf video compression tutorial MPEG-4 de OKI]

* [http://www.01net.com/Pdf/EIH200411110578031.pdf Noticia sobre MPEG-4 AVC] en francès

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[[Category:Video]]