Week 9 and 10 Flashcards
what is a video
a sequence of still images (photographs) that create the illusion of movement when played in succession
what is each still image called
a frame
movies on film played from ___ to ___ fps
24-30
tv was originally ___fps
29.97
computer displays video at at least ___fps
12-15
in digital video, each frame is a ___ graphic stored as 0 and 1
bitmapped
describe the sampling and quantization processes of film
sampling = each frame sampled into a discrete sample and each sample becomes a pixel
quantization process = assigning a value to each colour
what can we “sample” with MOTION
- Timing of the motion
- Sampling = frames
- Higher FPS = more accurate motion but a larger file size
still images use rgb but videos use
YUV (YIQ) or YCbCr for MPEG compression
what does the Y and UV in YUV stand for
Y = luminance Brightness UV = CbCr in YCbCr = chrominance (colour or hue)
black and white tv only used which part of YUV
Y because it had no chrominance (colour)
when we went from black and white to colour TV, we had to lose ___ because colour increased the file size of each frame
fps
the human eye can detect changes in ____ more easily than changes in __
brightness than colour
it is common for the ____ to be sampled less often because ___
chroma sample (UV) changes in colour are less noticeable
what is the format of colour sampling method
Y:U:V
u and v are colour hue
y is brightness
4:4:4 is no compression
4:4:4 colour sampling is how much compression
none
4:2:2 colour sampling is how much compression
33% on hue, reduced from 12 samples to 8
4:2:2 subsample rate means that out of four colours, two of them will disregard their own colour and take the colour of their adjacent pixel
- lose information
- and save space in your media
4:2:0 colour sampling is how much compression
50% on hue, reduced from 12 samples to 6
4:2:0 subsample rate means that 3 out of four colours will disregard their own colour and take the colour of the last one to save a lot of space in the end
if you want to compress colour, you ….
keep the brightness but take the averages of the colours
what kind of display did original tvs have
Interlaced display
what is interlaced display
uses 48 horizonal scan lines, our eyes see phosphor dots on the screen and an electron beam excites the dots and gun scans through the dots horizontally
only scans every other line odd and starts back up at the top and draws the even lines
- takes two passes, one pass= feild
what is a complete scan in interlaced display
starts at top left and scans each row until bottom right
each pass in an interlaced display is called a
field
what is a progressive display
what we use instead of interlacing
means the whole image is shown at once instead of displaying in passes
Download a sound file
have music embedded in web page