ViewCast Osprey PCI, User Manual

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Osprey PCI User Guide
ViewCast 81
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YUV12 planar - Also known as I420. This is a complex format in which there are in the aggregate
12 bits of data per pixel. Each pixel has 8 bits of luminance data. Each group of 4 adjacent pixels
arranged in a 2 x 2 square shares two bytes of chrominance data. See YUV Format Details.
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YVU9 planar - Similar to YUV12 planar, except that there are in the aggregate 9 bits of data per
pixel, and each byte pair of chrominance data is shared by 16 adjacent pixels arranged in a 4 x 4
square. See YUV Format Details.
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RGB32 - Each pixel has four bytes (32 bits) of data - one each for red, green, and blue, plus one
byte that is unused. The pixel has 256 shades of each of the three colors, for a total of 16.7 million
colors.
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RGB24 - Each pixel has three bytes (24 bits) of data - one each for red, green, and blue. This is
another “true color” mode with 16.7 million colors.
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RGB555 - Each pixel has two bytes (16 bits) of data. There are 5 bits each of red, green, and blue
data; the sixteenth bit is unused.
This is a “high color” mode, also known as “5:5:5.”
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RGB8 (Greyscale)
– The Osprey AVStream driver uses the RGB8 format for greyscale video.
RGB8 is a palletized format. Each pixel is represented by one byte, which indexes one of 256
colors in a color palette specified by the driver. The Osprey driver sets the color palette to
greyscale entries, and captures “Y8” luminance-only data.
YUV Format Details
YUY2, UYVY, YVU9, and YUV12 are YUV formats. In these formats, each pixel is defined by an
intensity or luminance component, Y, and two color or chrominance components, U and V. Since the
human eye is less sensitive to color information than to intensity information, many video formats
save storage space by having one luminance byte per pixel while sharing the chrominance byte
among two or more pixels. YUV is also similar to the color encoding used for analog color television
broadcast signals.
YUY2 mode, sometimes referred to as 4:2:2 packed mode, consists of a single array of mixed Y, U,
and V data. Each pixel has one Y (intensity) byte. Each pixel shares its U and V bytes with one of the
pixels horizontally next to it.
YUY2 uses the same number of aggregate bytes per pixel as RGB15, which is two. However, YUY2 is
more efficient than RGB15 because it stores relatively more of the intensity information to which
that the human eye is most sensitive.
UYVY mode is similar to YUY2 except that the bytes are swapped as follows:
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YVU9 and YVU12 are “planar” modes - the Y, U, and V components are in three separate arrays. It
is easiest to explain the format with an example: Let’s say you have a 320x240 YVU9 format. The
buffer has 320x240 bytes of Y data, followed by 80x60 bytes of V data, followed by 80x60 bytes of
U data. So each U and each V byte together contain the color information for a 4x4 block of pixels.
Similarly, a 320 x 240 YUV12 format has a 320 x 240 Y array, followed by a 160 x 120 U array, and
then a 160 x 120 V array.
Note: In the I420 format used by Osprey, the order of the U and V arrays is reversed from the order
in the YVU9 format.