Uyc File Format - Ultech Corporation DV2000 User Manual

34 ULTECH DV2000 User's Manual

5.5 UYC File Format

Digital Video (SMPTE 125M—4:2:2 Component) information consists of luminance (Y)
and color difference (CR & CB) values. For each line of active video there are 720 lumi-
nance values and 360 pairs of color difference values. The information for each line is
transmitted in the following order:
DV2000 groups this information into "pixel pairs". The first pixel pair of a line consists of
the Y values for both pixels (Y0 & Y1) and the CB & CR values for the pixel pair (CB0 &
CR0). The values are each 8 bits and are organized into two 16 bit words (Y0 is the least
significant byte of the Y word and CB0 is the least significant byte of the C word). Alpha
information is also used by DV2000 to control the opacity of the overlaid graphics. An 8 bit
alpha value is assigned to each pixel and organized into a third 16 bit word (alpha0 is the
least significant byte of the alpha word and aligns with the same pixel as Y0). There are 256
levels of opacity for each pixel. An alpha value of zero is transparent, so the pixel will be
100% background video. An alpha value of 255 is opaque, so the pixel will be 100% over-
lay. All of the values in between select levels of semi-transparency for the pixel.
The information for each pixel pair consists of 1 word of Y values, 1 word of color differ-
ence values, and 1 word of alpha values.
Image Positioning
When DV2000 inserts an image (UYC file) into the video, it must know where on the screen
to position the image. So, the DV2000 command to display an image requires three param-
eters: the UYC file name, an X offset, and a Y offset.
The X offset parameter specifies how much to offset the left edge of the image from the left
edge of the television screen. Since the DV2000 handles all image data in pixel pair format,
the X offset parameter value can only be between 0 and 360. If the X offset is zero then the
left edge of the image will align with the left edge of the television screen. If the X offset is
180 then the left edge of the image will be in the middle of the television screen.
The Y offset parameter specifies which video line will contain the first line of the image.
Video lines are numbered 1 to 262 for NTSC (1 to 313 for PAL) for each video field with
line 1 at the top. Note that video lines 1 to 20 are defined as the vertical blanking interval
(VBI) and are not displayed on the television screen. Also, line 21 (22 for PAL) is used for
the closed caption waveform. Because of this, the first displayed video line overlaid by the
DV2000 CG is line 23 (lines 1 to 22 are overlaid by the VBI waveform generator and lines
23 to 262 are overlaid by the character generator). Since the DV2000 performs image
processing on a field by field basis, the Y offset parameter can only be between 23 and 262
inclusive for NTSC (40 - 295 for PAL). If the Y offset is 23 (in NTSC) then the top edge of
the image will align with the top edge of the television screen. If the Y offset is 142 then the
top edge of the image will be in the middle of the television screen.
X offset = Number of pixel pairs between left edge of image and left edge of television
Yoffset = Video line number (of odd field) of the top edge of the image. Valid values
The discussion talks about alignment with respect to a television "screen". This, of course,
CB0, Y0, CR0, Y1, CB1, Y2, CR1, Y3, ..... CB359, Y718, CR359, Y719
screen. Valid values are 0 to 360.
are 23 to 262 for NTSC and 40 to 295 for PAL.