Access file: secondary down sampled derivative meant to serve as the easier to use file that is what our online access portal, the Digital Collections Platform (also referred to as Digital Library) displays in the IIIF viewer. Our file specifications are a 400ppi, 8bit, sRGB JP2000 with minimal sharpening added and object level target cropped out.
Ambient Light: Light from areas around your setup that is not intended to illuminate your subject, for example a computer monitor.
Aperture/F stop: How Open or Closed the Aperture is determining how much light, and the sharpness and depth of field, in an image. The lower the number (F/2.5 for example) the larger the hole, the larger the number (F/16 for example) the smaller the number, as this is a fraction, or "F stop", and that number is really representing an opening of 1/2.5 or 1/16; 1/2.5 > 1/16.
Auto Focus: The camera's ability to focus, or create the sharpest looking image possible, on an area of contrast without manual adjustments
Capture Plane: The level that the camera focuses when it's photographing, this would be where the material surface is while digitizing.
Color – Delta E 2000: measures the difference between expected values and measured values (color values)
Color Registration: a parameter tested for alignment of linear scanners, could indicate focus issue (very out of focus)
Continuous Light: Light source that is the same power intensity throughout digitization, often these create less warmth and good modern lights are LEDs with consistent and accurate color output.
Delta E (a* b*): measures the difference between expected values and measured values(whitebalance)
Depth of Field: The depth that the camera is in focus or out of focus when it's photographing, this is affected by the relationship between the focal length, distance to object and the aperture being used.
Device Level Target: A consistent color rectangle that is digitized to calibrate camera files to ensure accurate image quality. This is also sometimes used to create custom ICC profiles.
Field of View (FOV): What the camera sees, its frame of view might also be called a image or picture window.
Focal Length: The lens's focal length for our standard copystands is 72mm, this determines the field of view -- for transmissive materials we use longer glass, a 120mm lens, which fills the image better with the view of materials for smaller items such as 35mm photographic film negatives.
ICC Profiles: Affects color by way of using data to calibrate input or output (like monitors or images) based on standards from the International Color Consortium for specific color spaces.
ISO: the sensitivity set for the sensor of a camera, the larger the number the more light is collected but also the more likeliness for noise to present -- we like to shoot at the smallest ISO possible (often times the "native" ISO for best performance) which is usually 50ISO on our copystands, but we may adjust this as needed to balance our manual exposure triangle with Aperture and Shutter Speed.
ISO 19264: Standards set for cultural heritage photography for reflective imaging systems (as opposed to transparent setups such as digitizing photographic negatives) by the International Standards Organization (also abbreviated as ISO).
L Noise: upper boundary high, could test poorly if shooting a high ISO, sensors influence this
Lightness: Darks to lights of an image; Exposure measurement for accurate reproduction
Nyquist Frequency: limit to our resolving power
Object Level Target: A Consistent color bar that is digitized alongside items to ensure accurate image quality. This is also used to validate FADGI levels in our software.
Preservation File: Primary derivative meant to serve as the main file other derivatives may be created from for long term preservation purposes. Our file specifications are to include an object level target and crop outside-page-edge and create a 600ppi, 16bit, AdobeRGB uncompressed TIFF with all sharpening removed.
ROI : “region of interest”, the area being measured on the target or a given FADGI metric
Sampling Efficiency & Nyquist: Max amplitude SFR (can never go below 1, moving from 1 to 1.15 in new guidelines) resolution chart shows SFR curve for this (lightness, limits, set to all) - mapping contrast relationship to magnification “how much volume I have at a given resolution”, meaningfully resolving information is MTF 10 or limiting resolution, metric shows the smallest resolution showing meaningful detail (if unsharpened, this can be like 475 for a 600+ppi file), can show on Fadgi target things like if the lens is in plane – red is the worst, blue is the best (because red is the longest wavelength)
Sampling Frequency: the spatial resolution of an image (not its output specifications) - Pixels Per Inch (PPI) metric, math in program is computed by distance from dots on ends of the item level targets to measure this
Shutter Speed: How fast or slow the light is allowed through to the camera sensor, generally 1/125 shutter speed is good for limiting ambient light from affecting the white balance of an image. Strobes will often max out at 1/250 shutter speed. Cameras on copystands or tripods should have no or very few vibrations and can have much slower speeds as needed, but very slow shutter speeds may show motion blur more readily such as when working at a dual capture system and very quickly turning pages or moving a platen.
Strobe: Light source that presents a pop of light to illuminate the subject, use of a powerpack for very bright illumination is common as it requires adequate energy to work -- modeling lamps are often on to illuminate working space but the photographs are illuminated by the temporary strobe of light. Quality strobes have accurate and consistent light color output.
Tonescale: Tones are darks to lights of an image, the scale refers to the patchs (little squares on the targets) ranging from black and shadows, to low key grays, to medium gray or midtones, to high key grays and to whites or highlights. Exposure measurement for accurate reproduction can be seen via color readouts that measure the values in the color channels, or lightness channel in LAB color space, in the tonescale region of the targets.
Uniformity Masking: we do this with LCC’s (Lens Cast Calibration) and another term for it is Flat Fielding (in Lightroom, for example)
Whitebalance: The measured color temperature of an image to accurately reproduce the true colors of an object or scene in relation to the light sources present at time of capture. We set this value across color channels on raw files in Capture One based on patch 13 on the tonescale of the evaluation targets to calibrate our images accurately.
