Show Systems - Laser Graphics
Frames for Smoother Animations
Creating smooth moving and realistic animations requires that a large
number of key frames be digitized. This is time and labour
intensive. A well known animators technique called 'tweening' can be
used to create frames in between the key frames for smoother movements with
less digitizing. Points per second, Frames per second and their effect
on perceived flicker is also discussed.
For the purpose of this discussion, let's say you have digitized
10 key frames of a character animation and you plan to make a 20-frame animation
(running on twos) playing back at 15 FPS from the 10 original key frames.
Running on twos is an animation term that means that each key frame has been used
twice - in this case, once as a key frame and once
as a tweened frame.
Before we continue, we need to take into account the effect
of flicker and to optimize our animation in terms of points per frames and
frames per second (FPS) rate to minimize flicker.
Flicker is defined in the ILDA glossary as "A
perceptual effect in laser-drawn graphics when the laser cannot complete its
path before the eye's persistence of vision sees the image fade. The effect,
usually undesired, is that the image is flickering or pulsating."
In order to avoid the perception of flicker, it is best to keep the PPS and
FPS rates as high as possible. The lower limit of flicker perception is
between 16 and 18 FPS. Old black & white movies ran at 16 FPS and had
lots of flicker. Any images running slower than 16 FPS will have perceptible
and annoying flicker. To reduce flicker to a minimum, 20 FPS or above
is recommended - modern movies run at 24 FPS and flicker is almost imperceptible.
Here is a table of suggested operating parameters for various
frame rates on ILDA standard 12K and 30K scanners. Note that these are
suggested maximums for conservative ratings and may need to be adjusted to
suit your system. When in doubt, always go for the highest frame rate,
at the highest PPS rate, to reduce flicker. For example a, 10 FPS animations can easily be run at 20
FPS by drawing each frame twice.
Rated scanner speed
Suggested operating speed
Maximum points per frame
Note (1): It is suggested that you operate the scanners
below rated maximum speed to avoid thermal problems and to allow for
'headroom'. This is especially true if you plan to swap frames to
other systems which may not be exactly tuned to the rated speed.
Note(2): The recommended maximum points per frame do not divide
evenly into the total available points per second to allow for inter
frame/track blanking points.
You may want to adjust the number of points in each frame to meet the
recommendations outlined above so as to have minimal flicker in your
finished animation. Note that the 12K images running at 10 FPS and 12
FPS are likely to exhibit considerable flicker. Most graphics systems allow for independent
setting of the FPS and PPS rates. Thus, a 15 FPS animation can be
played back with a high PPS rate so as to minimize flicker while still
keeping the number of frames required reasonable.
Now that you
have the 10 frames edited (and saved), copy each frame to the following
frame (original frame 1 to frames 1 and 2, original frame 2 to frames 3 and
4, etc.) then save the 20-frame block. When played back at 15 FPS you will
have a animation that is quite jerky as each frame is a key frame and is repeated
You will now be editing the frames for tweening purposes.
Unlike typical frame editing, you will not be adding or deleting any
points. You will be using tools such as rotation, move and resize to
create minor differences in the frames.
In order to move or rotate only a
part of a frame, you will need to make only the points you want to move or
rotate active. Some laser graphics systems provide a way of selecting which points will be
active and can be edited. If all points are active, then any rotation,
sizing or other edits applied, will affect the entire image. With most
systems it is simplest to make all points in the frame inactive, then
activate only the points you wish to modify.
Go to frame 2 and compare the position of the character with the position of
the character in frame 3 (key frame 2). If, for example, the character is walking across the
screen, which foot is up and how far has it moved in the next frame (3)? You
can now make all points in frame 2 inactive except for the leg points. Use
the rotation and move tools to position the leg in frame 2 halfway between
its position in frame 1 and frame 3.
Simply moving one part of the frame (the leg) is not usually enough to
convey a smooth movement. Look at the angle of the body between frames 2 and
3. Use the rotation and move tools to adjust it to be halfway between the
positions in frame 1 and 3. You can look for other details to modify such as
arm position(s), clothing details, etc. The more subtle differences there
are between frame 1 (the key frame) and frame 2 (the tween frame), the
smoother the resulting animation will appear.
Testing tween frames
Test the editing of the tween frame by playing just frames 1
and 2 on the laser projector to see the differences (use a slower frame rate
that shows each frame two or three times). When you are happy with this
comparison, add frame 3 to the playback and observe the movement of the
character in the three frames.
When you are satisfied with the first three frames, repeat the editing
process on frame 4 (2nd tween frame) comparing it to frame 5 (key frame 3), then testing
it in playback between frame 3 and 4 then 3, 4 and 5 and so on.
Keep repeating this tweening process on even-numbered frames until you get
to frame 20. At this point it is cumbersome to keep switching from frame 1
to frame 20 to compare the movement. Copy frame 1 into frame 21 for tweening
and comparison purposes. When you have completed the tween frame editing,
save only frames 1 to 20 and discard frame 21 (which is a copy of frame 1).
Your animation should now move much more smoothly than the un-tweened
version. Now that you have completed your animation, adjust the output rate
of your system so that it is running at the desired FPS. Play the 20
animation frames again and you will see the animation as you intended it
with the tween frames smoothing the transitions between the movements in the
You will want to digitize at your system's default speed (to see the onset
of flicker and to accurately place points) but it is not likely that you
will want to play the animation at these speeds. The animation speed speed in frames per
second is more important for character movement than the speed setting in points per second
provided the PPS setting is high enough to eliminate flicker.
Computer tweening (morphing)
Most high-end graphics software provides a tweening or
"make frames" function. You need a starting frame and ending frame
(usually with the same number of points in each frame) and a minimum of one empty frame in
between (but usually more)..
The tweening function works by moving the points in a
straight line from their positions in the starting frame, to their positions
in the ending frame; via as many steps as there are blank frames available.
Some systems also allow for rotation of the image as it is being tweened.
Due to the linear nature of the point movement, the effect
is uncontrolled and looks more like the "morphing"
effect seen in movies and TV. This effect can be most useful and interesting when used with text, logos or
silhouette drawings (with no internal detail).
These effects are not very useful when tweening character animations since it is almost impossible to
insure that certain point numbers will form the same features in the image
in all key frames, you will have to hand-tween frames to obtain the best
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