diff -r 4816d766a08a -r f345bda72bc4 Symbian3/PDK/Source/GUID-47701648-CEC1-564C-A6BF-CC42E78E701F.dita --- a/Symbian3/PDK/Source/GUID-47701648-CEC1-564C-A6BF-CC42E78E701F.dita Tue Mar 30 11:42:04 2010 +0100 +++ b/Symbian3/PDK/Source/GUID-47701648-CEC1-564C-A6BF-CC42E78E701F.dita Tue Mar 30 11:56:28 2010 +0100 @@ -1,118 +1,118 @@ - - - - - -YUV -Pixel Formats OverviewThe YUV model defines a color space in terms of one luma (Y) and -two chrominance (UV) components. The YUV color model is used for analog encoding -of color information in television transmissions (PAL). Y stands for the luminance -component (the brightness) and U (Cb) and V (Cr) are the chrominance (color) -components. -

The requirement for a compatible signal transmission method -for both black-and-white and color information led to the invention of YUV -pixel formats. The UV signal was added to the existing luma component (Y) -black-and-white signal. This enabled color television transmissions within -the black and white infrastructure.

-

The YUV formats are divided into two groups:

- -
Subsampling -intervals

Chroma subsampling is the practice of encoding images -by implementing less resolution for chroma information (U (Cb) and V (Cr)) -than for the luma (Y) information.

The following table shows how U -and V are sampled relative to Y.

- - - -Subsampling scheme -Description - - - - -4:4:4 -No downsampling of the chroma channels. - - -4:2:2 -2:1 horizontal downsampling, with no vertical downsampling. Every scanline -contains 4 Y samples for every 2 U or V samples. - - -4:2:0 -2:1 horizontal downsampling, with 2:1 vertical downsampling. - - - -

The subsampling scheme is commonly expressed as a three part ratio J : a : b, -where,

    -
  • J is the horizontal -sampling reference (the width of the conceptual region). This is usually, -4
    • -
  • a is the number -of chrominance samples (Cr, Cb) in the first row of J pixels.
    • -
  • b is the number -of (additional) chrominance samples (Cr, Cb) in the second row of J pixels.
    • -

The horizontal subsampling interval describes how frequently across -a line a sample of that component is taken. The vertical subsampling interval -describes on which lines samples are taken.

For example, the UYVY -(4:2:2) formats have a horizontal subsampling period of 2 for both the U and -V components. This indicates that the U and V samples are taken for every -second pixel across a line. The vertical subsampling period is 1, which indicates -that U and V samples are taken on each line of the image. The following table -summarizes the horizontal and vertical subsampling intervals for the YUV 4:2:2 -formats.

- - - -Sample period -Horizontal -Vertical - - - - -Y -1 -1 - - -U -2 -1 - - -V -2 -1 - - - -
- 4:2:2 subsampling - -

Contrast this to a subsampling scheme of 4:4:4. This has a horizontal -subsample period of 1 for both the U and V components and a vertical subsample -period of 1 for both the U and V components.

- 4:4:4 subsampling - -

This reduction results in almost no perceivable visual difference.

- -YUV Pixel -Formats - Color Conversion - + + + + + +YUV +Pixel Formats OverviewThe YUV model defines a color space in terms of one luma (Y) and +two chrominance (UV) components. The YUV color model is used for analog encoding +of color information in television transmissions (PAL). Y stands for the luminance +component (the brightness) and U (Cb) and V (Cr) are the chrominance (color) +components. +

The requirement for a compatible signal transmission method +for both black-and-white and color information led to the invention of YUV +pixel formats. The UV signal was added to the existing luma component (Y) +black-and-white signal. This enabled color television transmissions within +the black and white infrastructure.

+

The YUV formats are divided into two groups:

+
    +
  • Interleaved formats in +which the Y, U (Cb) and V (Cr) samples are packed together into macropixels +that are stored in a single array.
    • +
  • Planar format in +which each component (Y, U (Cb) and V (Cr)) is stored as a separate array. +The final image is a fusion of the three separate planes.
    • +
+
Subsampling +intervals

Chroma subsampling is the practice of encoding images +by implementing less resolution for chroma information (U (Cb) and V (Cr)) +than for the luma (Y) information.

The following table shows how U +and V are sampled relative to Y.

+ + + +Subsampling scheme +Description + + + + +4:4:4 +No downsampling of the chroma channels. + + +4:2:2 +2:1 horizontal downsampling, with no vertical downsampling. Every scanline +contains 4 Y samples for every 2 U or V samples. + + +4:2:0 +2:1 horizontal downsampling, with 2:1 vertical downsampling. + + + +

The subsampling scheme is commonly expressed as a three part ratio J : a : b, +where,

    +
  • J is the horizontal +sampling reference (the width of the conceptual region). This is usually, +4
    • +
  • a is the number +of chrominance samples (Cr, Cb) in the first row of J pixels.
    • +
  • b is the number +of (additional) chrominance samples (Cr, Cb) in the second row of J pixels.
    • +

The horizontal subsampling interval describes how frequently across +a line a sample of that component is taken. The vertical subsampling interval +describes on which lines samples are taken.

For example, the UYVY +(4:2:2) formats have a horizontal subsampling period of 2 for both the U and +V components. This indicates that the U and V samples are taken for every +second pixel across a line. The vertical subsampling period is 1, which indicates +that U and V samples are taken on each line of the image. The following table +summarizes the horizontal and vertical subsampling intervals for the YUV 4:2:2 +formats.

+ + + +Sample period +Horizontal +Vertical + + + + +Y +1 +1 + + +U +2 +1 + + +V +2 +1 + + + +
+ 4:2:2 subsampling + +

Contrast this to a subsampling scheme of 4:4:4. This has a horizontal +subsample period of 1 for both the U and V components and a vertical subsample +period of 1 for both the U and V components.

+ 4:4:4 subsampling + +

This reduction results in almost no perceivable visual difference.

+ +YUV Pixel +Formats + Color Conversion + \ No newline at end of file