CAPTURING THE FRAME: FPS_ Shutter Speed_ CMOS/CCD Sensors_ Rolling and Global Shutters | YouTubeToText
YouTube Transcript: CAPTURING THE FRAME: FPS_ Shutter Speed_ CMOS/CCD Sensors_ Rolling and Global Shutters
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as i'm sure you know moving images
are created with multiple still images
exactly how many still images or frames
are taken in the camera
is known as frames per second
the usual number of frames per second
for films is around 24 or 25
fewer frames than this would appear
jittery and movements wouldn't look as
smooth as they should
more frames than this would simply mean
you would be getting more images
captured in one second
and therefore give clearer more defined
movements
high frame rates can also be used to
slow the footage down
in the edit if you captured 24 frames
per second in camera
and slowed this down to play back over
two seconds in the edit
there wouldn't be enough frames to make
the image look natural and smooth in
playback
therefore if you plan to slow the
footage down
you need to have the appropriate amount
of frames per second
captured in camera for example
if you filmed 100 frames per second and
spread this out across four seconds in
the edit
then the frames per second in playback
would be twenty five
doing this would make the footage four
times slower than watching it in real
time
if you filmed ten thousand frames per
second you would be able to play
back the footage 400 times slower than
real time
the more frames per second you capture
in camera the slower you can play it
back in the edit
however the more frames that are
captured
the more light is needed to capture them
this can be balanced out by adjusting
the iso
iris or by simply using bigger lights
another element to consider is the
shutter
when we talk about shutter angles this
refers to when things are shot on film
and there is a physical disk as the
shutter
the angle of which could be manually
changed
some digital cameras do also have a
physical shutter
although it is designed differently and
is more of a rectangle shape
for most digital video cameras there
isn't a physical shutter
it's more of a shutter effect created by
the camera's sensor
but the term shutter angle is still used
to describe the effect
caused as well as the equally used term
shutter speed
shutter angle or speed affects exposure
and motion blur the angle refers to how
much of the shutter is open
and therefore how long one single frame
is exposed to light for
when the angle of the shutter is
decreased
this reduces the motion blur of a moving
object because it's captured faster
however as a result of this the light
reaching the image will be lessened
as a general rule you want to have a
shutter angle of 180 degrees
this is half the shutter disc and is the
most common shutter angle to use
the equivalent of this in shutter speed
terms
would be 1 over double the frame rate
for example if the frame rate is 25
frames per second
then the shutter speed will be 1 over
50.
this means one fiftieth of a second
if you increase the frames per second to
fifty
then the shutter speed will be one
hundredth of a second
the way digital sensors create a shutter
effect without a real shutter
is by activating the photo sights on the
sensor like a switch
either being on or off this way
it can simulate the length of time a
physical shutter would have been
open for a rolling shutter
means that the photo sites are activated
from top to bottom
or side to side this technique can
sometimes give
unusual effects like the jello effect
on the other hand the newer global
shutter doesn't have this problem
because all of the photo sites are
switched on at the same time
this way the motion blur can still be
regulated but you don't get any
distortion as a side effect
the sensor needs to convert light into
digital information
this can either be achieved with a ccd
sensor
or a cmos sensor ccd
sensors work by sending the charge from
the photo sites
one row at a time and takes them to a
chip elsewhere to be converted into
information
cmos sensors are designed differently
instead of converting information
elsewhere in rows
each photo site has its own tiny
converter next to it on the sensor
the downside to this is that more noise
is accumulated on the image because of
this
however it is the cheaper sensor
designed to have
on the other hand ccd sensors are more
expensive
but create higher quality low noise
images
thanks for watching like this video if
you found it useful
and we'll see you next time
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