picture types n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Picture types PowerPoint Presentation
Download Presentation
Picture types

Loading in 2 Seconds...

play fullscreen
1 / 11

Picture types - PowerPoint PPT Presentation


  • 108 Views
  • Uploaded on

Picture types. There are three types of coded pictures. I (intra) pictures are fields or frames coded as a stand-alone still image. These are coded without reference to other pictures. Moderate compression is achieved by reducing spatial redundancy but not temporal redundancy.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Picture types' - alva


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
picture types
Picture types
  • There are three types of coded pictures.
  • I (intra) pictures are fields or frames coded as a stand-alone still image.
  • These are coded without reference to other pictures.
  • Moderate compression is achieved by reducing spatial redundancy but not temporal redundancy.
  • They allow random access points within the video stream.

tMyn

slide2
As such, I pictures should occur about two times a second.
  • I pictures also should be used where scene cuts occur.
  • P (predicted) pictures are fields or frames coded relative to the nearest previous I or P picture, resulting in forward prediction processing.
  • P pictures provide more compression than I pictures, through the use of motion compression, and are also a reference for B pictures and future P pictures.

tMyn

slide3
B (bidirectional) pictures are fields or frames that use the closest past and future I or P picture as a reference, resulting in bidirectional prediction.
  • B pictures provide the most compression, and decrease noise by averaging two pictures.
  • Typically, there are two B pictures separating I or P pictures.

tMyn

slide4
Compression performance could be something like:

Type I, Compression 7:1

Type P, Compression 20:1

Type B, Compression 50:1

An an average, Compression 27:1

tMyn

slide5
Macroblocks in P pictures are coded using the closest previous I or P picture as a reference, resulting in two possible codings:

intra coding

    • no motion compensation

forward prediction

    • closest previous I or P picture is the reference

tMyn

slide6
Macroblocks in B pictures are coded using the closest previous and/or future I or P picture as a reference, resulting in four possible codings:

intra coding

    • no motion compression

forward prediction

    • closest previous I or P picture is the reference

backward prediction

    • closest future I or P picture is the reference

bi-directional prediction

    • two pictures used as the reference: the closest previous I or P picture and the closest future I or P picture

tMyn

slide7
To enable backward prediction from a future frame, the coder re-orders the pictures from the natural display order to a ”transmission” (or ”bit-stream”) order so that the B-picture is transmitted after the past and future pictures which it references, Figure 1.
  • This introduces a delay which depends upon the number of consecutive B-pictures.

tMyn

slide8

FORWARD PREDICTION

PICTURE DISPLAY

ORDER

1

2

6

3

5

7

4

4

2

6

1

3

7

5

PICTURE TRANSMIT

ORDER

BI-DIRECTIONAL PREDICTION

BI-DIRECTIONAL (B)

PICTURE

PREDICTED (P)

PICTURE

INTRA (I) PICTURE

Figure 1. MPEG-2 I-, P and B pictures.

tMyn

slide9
A group of pictures (GOP) is a series of one or more coded pictures intended to assist in random accessing and editing.
  • The GOP value is configurable during the encoding process.
  • The smaller the GOP value, the better the response to movement (since the I pictures are closer together), but the lower the compression.

tMyn

slide10
In the coded bitstream, a GOP must start with an I picture and may be followed by any number of I, P or B pictures in any order.
  • In display order, a GOP must start with an I or B picture and end with an I or P picture.
  • Thus, the smallest GOP size is a single I picture, with the largest size unlimited.
  • Each GOP should be coded independently of any other GOP.

tMyn

slide11
However, this is not true unless no B pictures precede the first I picture, or if they do, they use only backward motion compensation.
  • This results in both open and closed GOP formats.
  • A closed GOP is a GOP that can be decoded without using pictures of the previous GOP for motion compensation.

tMyn