Instruction manual

HDE-3000 - 68 -
Image Positioning
When HDE-3000 inserts an image (UYC file) into the video, it must know where on
the screen to position the image. So, the HDE-3000 command to display an image
requires three parameters: 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 HDE-3000 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 HDE-3000 GI is line 23 (lines 1 to 22 are overlaid by the VBI
waveform generator and lines 23 to 262 are overlaid by the graphics inserter). Since the
HDE-3000 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 screen. Valid values are 0 to 360.
Y offset = Video line number (of odd field) of the top edge of the image. Valid values
are 23 to 262 for NTSC and 40 to 295 for PAL.
The discussion talks about alignment with respect to a television “screen”. This, of
course, does not take into consideration the fact that the image raster on televisions is
overscanned. So a portion of the image will be “cut-off” if it is placed at the very edges
of the image raster. HDE-3000 has a built-in safe title area generator to help you locate
images in a location that will be visible on consumer television sets.