Field Ordering in Stills and Animations
The graphics files that are uploaded to the DPS-475 and DPS-575 are originally
stored in standard graphics file formats. These file formats to do not distinguish
between fields or otherwise deal with interlace. Industry convention is to treat each
"row" of the file as a separate "line" of video on alternating fields. All of the odd rows
will end up in one field and the even rows in the other field. For still images this
convention works fine, and it doesn't matter which row ends up in which field. Any
parts of the image that are only one row tall will appear to flicker at the field rate
(60Hz). Graphics software which is intended to produce graphic files for video
applications will perform some vertical filtering to avoid this situation. On the
computer screen (which is not interlaced) the image may look “soft” as a result.
On the DPS-475 (and DPS-575 in NTSC mode), the first row of the graphics file will
be put into field 2, and the second into field 1. Thus, over the entire height, the even
rows (if you start counting from zero on the first row) will be in field two and the odd
rows will be shown in field one. On the DPS-575 in PAL mode, however, the
opposite is true. For still images, this detail doesn't matter. However, for animations it
is critically important.
A smooth animation requires motion blur. To show this blur as it would be captured
by a real video camera, the animation must be rendered as separate fields, at 30
frames per second (60 fields per second) for NTSC [most animation software does
not support the precise frame rate of 29.97Fps]. Most animation software is aware of
broadcast video and can do this very easily. If your software is more primitive, you
could render your sequence at 60 frames per second, then take the even lines of the
even frames, and the odd lines of the odd frames to make a new sequence that is 30
frames per second (with two fields per frame). In rendering for PAL, you would do
the same, but at 25 frames per second or 50 fields per second.
Field two comes out after field one in time, and that's where they get their names
from. Therefore, for an NTSC animation, you should have field one (the first field in
time) starting on the second row of the graphics file (and on the following odd lines).
However, for a PAL animation, the opposite is true: field one should be the first row
of your graphics file (and subsequent even lines). Since an animation intended for
PAL or NTSC will normally be rendered with a particular frame rate in mind (either
30 or 25), this is not a serious restriction.
Most animation software (for example 3D Studio Max or LightWave 3D) has a
software control for determining field dominance, which must be selected by the user
before rendering to match these requirements.
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DPS-475/575 Service Manual
Original Graphics File:
Row# Image
0 ---X---
1 --X-X--
2 -X---X-
3 X-----X
4 -X---X-
5 --X-X--
6 ---X---
NTSC:
Field Image
2 ---X---
1 --X-X--
2 -X---X-
1 X-----X
2 -X---X-
1 --X-X--
2 ---X---
PAL:
Field Image
1 ---X---
2 --X-X--
1 -X---X-
2 X-----X
1 -X---X-
2 --X-X--
1 ---X---
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