Terms Flashcards
(30 cards)
What is interpolation in video
Interpolation is a mathematical technique used to estimate unknown values between known data points
Visually Lossless
type of image compression where data is discarded during compression, but the lost information is so subtle that the human eye cannot detect any difference in quality compared to the original image
Black / White scale vs grayscale
A “black/white scale” refers to only two color options, pure black and pure white, while “grayscale” encompasses a range of shades of gray between black and white
Lossless
compression means that no data is lost during compression, preserving the original image perfectly, even if it results in a larger file size; reversible data compression
Data streams
the continuous flow of digital data that makes up a video
Compression
the process of reducing the file size of a video by eliminating redundant information between frames, allowing for more efficient storage and transmission of video content while minimizing the loss of visual quality;
what is a macroblock
A video macroblock is a unit of pixels used to compress and encode video data. Macroblocks are the basic building blocks of video compression.JPEG, MPEG-1, H.262/MPEG-2 Part 2, and H.264/MPEG-4 AVC
lossless formats
H. 264 Lossless, H. 265 Lossless, Motion JPEG Lossless, Apple Animation Quicktime RLE, Autodesk Animator Codec
lossy
reduce quality in order to maximize compression , irreversible compression
lossy formats
HEVC, MPEG4, H.264, AVC,
codec
video codec is a set of instructions or algorithms for the “co”ding and
“dec”oding of a digital video stream. It is used when compressing a digital video
stream during the capture/encoding process and when decompressing a video
stream during playback.
What is AOI mean
Area of Interest
Explain recovery of images from a low light video clip
-Adjust lighting using level or Exposure filter
-Stabilize if needed
- Frame average if needed
Can you modify the settings of a still and then make it into a video clip?
Use Sequence Loader
1. Load > Sequence Loader or drag/drop in Amped FIVE
Bicubic Interpolation
Bicubic goes one step beyond bilinear by considering the closest 4 × 4 neighborhood of known
pixels — for a total of 16 pixels. Since these are at various distances from the unknown pixel,
closer pixels are given a higher weighting in the calculation.
Bilinear interpolation
considers the closest 2 × 2 neighborhood of known pixel values
surrounding the unknown pixel. It then takes a weighted average of these 4 pixels to arrive at its
final interpolated value. This results in much smoother-looking images than the nearest
neighbor.
Neighbor interpolation
doubles
What is the difference between visually lossless and absolute lossless compression. Can
you describe a scenario in which you would use one method over the other?
Visually lossless compression is compression that allows the visually quality of the
video to be identical to the original quality of the video to the human eye.
Lossless compression is compression that allows the same quality of video as the
original.
What are the three primary types of data streams that can be contained in an AVI media
file?
Video, audio, and text.
For an 8-bit grayscale image, how many possible brightness values are there for each pixel?
28 or 256 (from 0 to 255).
Name all of the factors of a digital video recorder (DVR) that control the maximum length of
time that can be recorded before it begins to overwrite itself.
Capacity of hard drive(s)
* # active cameras attached to the DVR
* System frame rate
* Frame rate per camera
* Video resolution (e.g., number of pixels captured in each image)
* Quality/compression setting
* Color vs. black & white capture
* Constant capture rate vs. motion/triggered activation
As a video forensic examiner, what would you consider your highest priority when
documenting your analysis?
Reproducibility
You receive a standard Windows Media Video (WMV) video file exported from a DVR, which
features an overlaid date and time stamp out to the seconds. Upon playback, you note that
the file is playing back with a constant 30 frames/second rate with no duplicated frames, but
is running faster than real-time based on the overlaid time stamp Please explain the
process(es) by which you can correct the speed of the video file to achieve real-time
playback.
Pick a frame near the beginning of the file and a frame near the end of the file;
determine the length of time between them based on the overlaid date/time stamp
(inclusive of the first and last time stamp seconds); determine how many video
frames there are from the first selected frame to the second; calculate the overall
number of frames per time stamp second (divide the number of video frames by
the length of time between them based on the overlaid date/time stamp);
determine the % of speed correction needed to be applied to the 30 frames/second
video to achieve real-time playback; and apply the % speed correction to the WMV
file in a non-linear video editor.
For example, if a time range of 10 time stamp seconds is comprised
of 60 video frames, then the overall number of frames per time stamp second is 6
(60÷10). Therefore, to correct the 30 frames/second video to 6 frames/second, a
speed correction of 20% would need to be applied (6÷30 = 1÷5 = 20%). Stated
another way, you would need to lengthen the 30 frames/second WMV video to 5
times its length to achieve real-time playback.
The key to the answer is that the overlaid date/time stamp must be used as a
reference to determine the appropriate correction factor.
What is a pixel
Picture element – smallest controllable element in a digital image. Each contains
information about color and brightness. (RGB) Series of pixels contruct what is called
a raster image.
