Mikrotron eosens TS3, Руководство пользователя, Страница: 110 / 120

TS3 User Manual
11S-3000M
page 101
Application Note 4: Frame Rate, Resolution, and Exposure
Scale and Resolution/Frame Rate
Selecting the p r oper resolution and f r ame rate for a given high-speed event is important. It is
based on the Field of View (FOV) required to get a good image of your object of interest and the
speed at which the object will move through that FOV.
For example, if you wish to image an automobile travelling at 50 mph across an intersection, full
resolution and a re lati v ely slow frame rate will work because your field of vi e w (FOV) will be large
and the car will not be moving through it very quickly.
Imaging a bird travelling at the same speed will require a much smaller FOV as the bird is 1/20th the
size of the car. If you wish to use the same scale (object size/FOV), the FOV becomes 1/20th the size
and the bird moves through it 20x as fast.
If you got acceptable imaging of an auto at 60FPS, it may take 1250FPS to get similarly acceptable
imaging of a bird at moving the same speed.
Aliasing and Frame Rate
If you are imaging a motion th a t is cyclical in nature like a wheel spinning or a lever moving up and
down, it is important to use a high enough frame rate to avoid motion aliasing. If y ou know the
speed of the object, use a frame rate at least a few times as f ast as the repetition r ate to get a
valid characterization of the motion. If y ou don’t know the speed, use as high a frame rate as
possible to start with and adjust from there. (Be sure to analyze the movement one frame at a
time as the
playback speed may cause aliasing as well.)
Generally you will choose to use the largest resolution possible f or the frame rate required. This
will give you the best definition of our object of interest. Smaller resolutions m a y be desired in
order to increase the record time. Choosing the rig h t shu tt er speed is dependent not only on the
speed at which an object is travelling through the FOV, it is also dependent on how the imagery is
going to be used.
For motion anal
y sis it is best to get as short an exposure as possible in order to limit motion
blu r . (Motion blur an be defined as the number of pi x els traversed by an edge of an object
during an exposure.)
For smooth video, on the other hand, long exposures are best. These make for more att
r acti v e
movies, but blurry stills .