Preservation

Glossary of QA/QC Terms

Acceptable Quality Level (AQL): This is usually defined as the worst case quality level, in percentage or ratio, that is still considered acceptable. QA, (Quality Assurance), may be in charge of monitoring AQLs. If a produced unit can have a number of different defects, then demerits can be assigned to each type of defect and product quality measured in terms of demerits. As an AQL is an acceptable level, the probability of acceptance for an AQL lot should be high. (Typical values between 92.74% to 99.999996% for six sigma, see Cpk compares to PPM for value reasons) Some sources characterize an acceptable quality level as the highest percent defective that should be considered reasonable as the process average. Usually monitored using SPC, (Statistical Process Control), at the production levels by Quality inspection. [All formats]

Active Pixels The area of the picture excluding the black bars (percentage) (Source: Baton) [Digital moving image formats]

Aimpoint: Black: Black point is the darkest spot or the lowest RGB levels for color files and highest % black for grayscale files (FADGI) [Digital still image formats]

Aimpoint: White: The lightest spot or the highest RGB levels for color files and lowest % black for grayscale files within the image (FADGI) [Digital still image formats]

Audio Channel: The number of full bandwidth channels in an audio file. (Baton) [Digital audio formats]

Audio Clipping: The abrupt truncation of a signal when the signal exceeds a system's ability to differentiate signal values above or below a particular level. (FADGI Glossary) [Digital audio formats]

Audio Tracks (Number of): The number of audio tracks in a file. (Source: Baton) [Digital moving image and audio formats]

Average Bit Rate: The average amount of data transferred per over period of time (Source: Baton) [Digital moving image]

Bits Per Pixel: The number of bits used to represent the color information of a pixel. Baton detects the acceptable number of bits per pixel of picture in a video. (Source: Tektronix)[Digital moving image formats]

Bit Rate: The number of bits that are conveyed or processed per unit of time, most often (but not exclusively) employed when discussing time-based media like sound or video. (FADGI)[Digital moving image and audio formats]

Bits Per Sample: The number of bits used to record information from each audio sample. (Baton)[Digital audio formats]

Black Bars: A term used in television production to describe the effect that occurs when a 4:3 image is viewed on a 16:9 screen. Black bars will be seen on the sides of the screen. (Tektronix) [Digital moving image formats]

Brightness: The value of a pixel along the black-white axis. (Tektronix)[Digital moving image formats]

Cadence Break: A break in the frame order or cadence in video.[Digital moving image formats]

Chroma Format: NARA uses a chroma sampling format of 4:2:2 which is a commonly used term for component digital video. The numbers 4:2:2 denote the ration of the sampling frequencies of the single luminance channel to the two color difference channels. For every four luminance samples, there are two samples of each color difference channel. Baton checks to ensure this sampling format is correct in our AVI files. Note: See ITU-R BT.601 for more specifics on this standard. (Tektronix and ITU-R BT.601)[Digital moving image formats]

Color Bars (SMPTE): A video test signal typically containing eight basic colors (white, yellow, cyan, green, magenta, red, blue, and black). It is used to check the chrominance functions of color NTSC TV systems. (Tektronix)[Digital moving image formats]

Contrast: The difference between the white and black picture levels. (Tektronix)[All formats]

Delta E: Delta E (or color encoding error) Color Encoding Error measures the difference between what the actual target colors are and what they would be if the RGB values of those color patches are decoded according to a specified working color space standard or device color profile. Delta E (ΔE) is the unit for measuring this error. (FADGI)

Duration: Length of time that a particular effect or section of audio or video material lasts. (Tektronix)[Digital moving image and audio formats]

Field Order: Interlaced field that is displayed first. Often referred to as either top or bottom field first.[Digital moving image formats]

File Size: Amount of data in a file. Usually measured in bytes, K (kilobytes) MB megabytes, or GB (gigabytes) [All formats]

Frame Rate: The rate at which frames of video data are scanned on the screen. In an NTSC system, the frame rate is 29.97 frames per second (Fps). This changed from 30 Fps so that the color subcarrier could be interleaved between both the horizontal line frequency and sound carrier. Baton detects the frame rate of a video frame, which will be 29.97. (Tektronix)[Digital moving image formats]

Freeze Frames: A frame that occurs when pictures in a video appear to standstill even though the video is playing. (Baton) [Digital moving image formats]

Image Cropping: an image-editing/processing technique whereby an unwanted portion or portions of a digital image are removed. Cropping is usually performed to remove some portion of one or more outside edges of the image. Cropping may be performed in different manners to the same image depending on its intended use. For example, on a the original or master scanned image, a very conservative crop may be used to remove portions of the image outside of the borders of the object being imaged to remove empty space. An access derivative may be cropped more aggressively. For example, a book page may be cropped in a manner that preserves all the text of a page, but removes some of the bordering "white space." And finally, a thumbnail image may crop some of the actual content, to highlight a particular feature or "look." (FADGI)[Digital still image formats]

LFE Channel: Optional channel that carries a separate, limited, frequency bandwidth signal that complements the main channels. It delivers bass energy specifically created for subwoofer effects or low-frequency information. Often between 3-120 Hz. [Digital audio formats]

Mismatch in Audio and Video Duration: Variance between audio and video track duration within a video (Baton)[Digital moving image formats]

Modulation Transfer Function (MTF): The sharpness of an imaging system can be characterized by its Modulation Transfer Function (MTF), which is generally equivalent to the Spatial Frequency Response (SFR). One approach to measuring this parameter employs a target with black and white bands of increasing spatial frequency (see examples at http://www.normankoren.com/Tutorials/MTF.html). (There are also other methods for measuring MTF and/or SFR.) As the bands get closer together, it becomes more and more difficult for an imaging system to reproduce them so that the bands can be distinguished: what had been black and white blurs into gray. On the image of the target, where the frequencies of the bands remain clear and distinct, the MTF is said to be 100 percent. When the contrast falls to one half of its original value, the MTF at that point on the target is 50 percent. Experts in fields like photography state that humans perceive high levels of image sharpness at the 50 percent point. In some other image-dependent scientific fields, however, the 10 percent point is used to determine the resolution of an imaging system.[Digital still image formats]

Noise: (ISO 15739) Random variation of brightness or color information in images produced by the sensor and circuitry of a scanner or digital camera. Unwanted variations in the response of an imaging system. Total noise - all the unwanted variations captured by a single exposure.[Digital still image formats]

OpenDML AVI File Format Extension: File standard that allows for AVI files larger than 2 GB. Baton checks to make sure NARA’s AVI files meet this DML specification. [Digital moving image formats]

Orientation proportions/distortions: The alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation, usually unwanted. (FADGI)[Digital still image formats]

Reference Targets: Reference targets can be used to assist with adjusting scanners and image files to achieve objectively “good images” in terms of tone and color reproduction. [Digital still image formats]

Resolution (Still Image): Measure of the ability of a camera system, or component of a camera system to depict picture detail. (ISO 12233). Resolution metrics include: Resolving power, Limiting resolution, Spatial frequency response, MTF and OTF.[Digital still image formats]

Resolution (Video): The basic measurement of how much information is on the screen (or amount of detail in an image). A typical NTSC resolution is 720 x 486, which refers to the number of distinct pixels in the horizontal axis by the number of horizontal lines. (Tektronix) [Digital moving image formats]

Resolution Change: The change in the resolution of a picture. (Baton) [Digital moving image formats]

Sampling Frequency: The frequency that a signal is sampled along an axis of time or space. (FADGI Glossary)[Digital audio formats]

Scale Reference: An accurate dimensional scale used as a reference for the size of original documents. (FADGI) [Digital still image formats]

Skew: The angle of deviation in a digital image from the paper edge, text lines or other visual reference elements. Skew is expressed numerically as the tangent of the deviation angle in degrees, either clockwise or counterclockwise. It applies to the angle of two-dimensional image orientation. Skew is a common occurrence in automatic document feeder scanning when the paper deviates from the paper path. (FADGI) [Digital still image formats]

Spatial or Geormetric Distortion: : The deviation of any imaged point from it intended or aim spatial position relative to the input object.[Digital still image formats]

Spatial Frequency Response: (ISO 12233, 16067-1, 16067-2). Measured amplitude response of an imaging system as a function of relative input spatial frequency. The SFR is normally represented by a curve of the output response to an input signal of unit amplitude, over a range of spatial frequencies (ISO 12233). Spatial Frequency Response (SFR) measures an imaging system’s ability to maintain the relative contrast to increasingly finely spaced features. (FADGI). Measures an imaging systems ability to maintain the relative contrast to increasingly finely spaced features (Don Williams). A number of important performance measures can be derived from this single function. Closely spaced or high frequency features test the limiting resolution of an imaging system. An imaging systems response to moderately space or mid-frequency features provide insight on the ability to re-purpose an image for a variety of use cases without introducing artifacts. For digital imaging system it is even possible for the resolution to be too good thus introducing aliasing artifacts. As part of the processing that occurs on delivered image files, sharpening is often applied. Often these sharpening operations are over-aggressive and cause images to appear un-natural or synthetic. (FADGI)[Digital still image formats]

Spatial Resolution: Determines the amount of information in a raster image file in terms of the number of picture elements or pixels per unit of measurement. [Digital still image formats]

Test Tone: A 1000 Hz audio tone used to calibrate playback equipment. [Digital audio formats]

Tone Response Curve (TRC) ISO 14545 – Opto Electronic Conversion Function: The Tone Response Curve of a digital camera or scanner determines the lightness, darkness, and contrast of a displayed image (FADGI). This is equivalent to OECF in the Metamorfoze Preservation Imaging Guidelines. OECF - relationship between log of input levels and corresponding digital output levels for an opto-electronic digital image capture system (ISO 14524)[Digital still image formats]

Updirection Conversion: Conversion of video content from a lower resolution to a higher resolution. (Baton)[Digital moving image formats]

Universal Test Target (UTT): Arrangement of test patterns designed to test particular aspects of an imaging system. [Digital still image formats]

Video Format: The format of a video such as PAL, NTSC, or HD. [Digital moving image formats]

Video Tracks (Number of): The number of video tracks in a file. (Baton) [Digital moving image formats]

Video Signal Levels: The chroma and luma levels in a video. Chrominance (also referred to as chroma) is the depth or saturation of color and luminance (also referred to as luma) is the brightness signal. Baton checks these values within a NARA defined range of what is appropriate to detect smeared colors and blown out highlights. (Tektronix)[Digital moving image formats]

White Point: The point on the chromaticity diagram where a source appears white under the viewing conditions. (Tektronix) [Digital moving image formats]

Top of Page

Preservation >

The U.S. National Archives and Records Administration
1-86-NARA-NARA or 1-866-272-6272

.