General Definitions Flashcards
Hash
A fixed-length, statistically unique identifier or digital fingerprint generated by running the data from the object being hashed through an algorithm
IFrame
Intraframe - least compressed frame, most information, refers to itself, denotes beginning/end of GOP
Container
A container format (informally, sometimes called a wrapper) or metafile is a file format that allows multiple data streams to be embedded into a single file, usually along with metadata for identifying and further detailing those streams. The Format or Container, stores the audio, video, subtitles, and other elements that make up your video
Codec
The Codec encodes and compresses, then decodes and decompresses the data that makes up your video. It is about what comes out of the camera; the filming and recording process.
Identified by the container; installed to the OS and called by the player when file is loaded; affects how multimedia appears during encoding
Pixel
Picture element - the basic unit of programmable color on a computer display or in a computer image
8-bit
A mode where the image uses 256 shades of red, blue, and green respectively, for a total of 16.8 million colors
True color
When all three RGB colors are combined in each pixel in 8-bit mode, 16.8 million different colors are possible (if each channel was lowered by one bit, there wouldn’t be enough possible shades to mimic human eyesight)
16-bit
Uses 16 channels per RBG color per pixel; means over 281 trillion color possibilities
Histogram
A graphical representation of tonal values in a digital image; used to understands contrasting values of black (0) and white (255) in an image
Frame averaging
A technique where multiple images are averaged out to remove random noise; best when target isn’t moving
Interpolation
The creation of new pixels that did not exist before resizing, based off existing pixels
Nyquist theory
Says to accurately recreate an analog signal, the signal must be sampled AT LEAST TWICE the highest frequency contained in the signal; prevents dropped frames during multimedia capture
Authenticity
Is the video an accurate representation of the area/scene/environment?
Depends on what issue the evidence is intended to answer
Authenticity is dependent upon what the evidence is supposed to represent
Florida Vs muro
Integrity
Is the video unchanged from acquisition/have all steps to clarify the evidence been documented
Extraction
The process of recovering data from its native environment
FVA must determine most accurate/best preservation method for each digital video, which methods they have in their toolkit
Preservation
The process of insuring evidence is not lost or altered
Challenges - possibility of overwriting, physical barriers, passwords, authority/consent
Analysis
The process of performing clarification techniques and drawing conclusions from clarified images
Rods
Photosentive cells responsible for monochromatic vision; concentrated on periphery of retina
Cones
Photosensitive cells responsible for color vision; concentrated in center of retina; classified by wavelengths they are sensitive to
Short wavelength cells - blue sensitive
Medium wavelength cells - green sensitive
Long wavelength cell - red sensitive
IP camera
Internet Protocol cameras digitizes (samples and quantizes) values from a CCD or CMOS, compresses resulting images, and streams video using internet protocols; usually have built-in web servers; generally encrypted so only intended audience can view them
Native resolution
Fixed grid pattern of LCD monitor; number of pixels wide by pixels high
Pixel matrix
Configuration of pixels in a digital image or displays; ex: 1920x1080 is pixel matrix for 1080 tv with a 16:9 aspect ration
Cloud
A cloud computing model that stores data on internet through a cloud computing provider who manages storage as a service
Edge storage
Data stored within camera
Centralized local storage
A hub/router/removable storage device
Compression
The process of reducing the size of a data file OR the process of reducing the volume of data required to store/transmit info
Eliminates redundancy/discards less important data
Lossless compression
No data is lost/all data can be retrieved in original form
Lossy compression
Compression in which data is lost and cannot be retrieved in original form
Quantization
Allows us to group like coefficients together
Quantization matrix is used to divide the DCT matrix; result is rounded to nearest integer
Stored with image so process can be reversed
WHERE THE MOST COMPRESSION/LOSS OCCURS
Entropy encoding
Used to reduce size of data
Information is transformed from two dimensions to one by recording values of matrix in a zigzag pattern
Spatial compression
Compression which uses similarity of pixels close in proximity to each other; applied within a single i-frame
Temporal compression
Compression which takes advantage of similarities between frames close in time; applied to each frame in a GOP
PFrame
Predictive frame which requires info from a preceding i or P frame, divided into macroblocks
BFrame
Bidirectional frame which references the closest two I or P frames
Artifact
Error caused by compression; things that are added or missing from video during compression
Integrity
Is the evidence complete and unaltered since the time of acquisition?
Lack of integrity indicates unknown change to evidence, which can compromise the ability to prove its authenticity
Clarified evidence should be able to be verified against original evidence (by documenting steps needed to recreate process)
Quantization noise
The difference (error) between original analog signal and signal produced from digitized values
Clipping
Occurs when a signal falls outside minimum or maximum values that can be represented during quantization; results in a loss of contrast
Aliasing
Occurs when sample rate is less than adequate to accurately reproduce signal
Preservation request
Sent to obtain cloud video footage for 90-180 days
Macro block
Group of pixels operated upon as a unit
