Table 1.
Important display specifications (medical grade, consumer off the shelf, and professional grade) and definitions, grouped by feature type (original work)
| Specification | Definition and salient points |
|---|---|
| Panel type | The primary technology and design of the display which affects many downstream characteristics. This includes CRT, external backlit, and emissive displays |
| CRT | Older display type that generates images through the deflection of a beam of electrons to the screen surface, currently considered to be a “dead” technology when compared to LCDs |
| LCD | Display type that utilizes an array of liquid crystal cells manipulated by electric fields, has largely supplanted the earlier CRT displays in both COTS and MG markets. There are multiple LCD panel technologies, with each having differences in the arrangements and properties of their individual liquid crystal cells [Table 2]. LCDs generally require an LED or CCFL backlight to produce an image with sufficient luminance |
| Viewing angle | A measurement given in degrees denoting the maximal deviation from the central axis, wherein a viewer can still perceive the image displayed on a display without degradation of brightness and contrast. Note that this is typically given as a symmetrical measurement from a center point. As an example, a 90° would allow the viewer to move 45° in either direction while still maintaining image adequacy |
| Backlight bleeding | Artifact where the backlight can be seen even while the display is showing a dark color. This is due to a lack of complete opacity in the LCD material and is a characteristic weakness of certain panel types (e.g., IPS) |
| Luminance | Objective measurement of light intensity (compare with brightness, below), expressed as cd/m2 (candela/meter squared) in the SI measurement system, fL in the US/English system, or nits (deprecated term, however still commonly used in COTS specifications). Typically used when referring to light being generated or reflected, different from illuminance (below) |
| Brightness | Subjective measure of light intensity by the user, expressed as unlabeled units or as a percentage. Literally denotes the light perceived by the user being generated or reflected from a display. Does not have a linear relationship with luminance |
| Illuminance | Objective measurement of ambient light intensity present in the surrounding environment, measured in lx |
| Contrast and contrast ratio | Static contrast refers to the ratio (e.g., 1000:1) of the maximal luminance to minimum luminance possible for the display at a static point in time. Dynamic contrast refers to the same ratio but at different points in time. Reported dynamic contrast ratios are often much higher than static contrast ratios (1,000,000:1) and the popular perception is that, while sounding impressive, dynamic contrast ratios are not reliable specifications for comparing displays |
| Pixel | A.k.a. picture element, denotes the smallest distinct controllable point of a display panel |
| High dynamic range | Technology that allows for a more accurate portrayal of color or shades of gray across a wider, extended luminance spectrum (i.e., produces darker shadows and brighter lights) |
| Color depth (or bit depth) | Number of bits (a binary representation of digital information in the form of on/off, true/false, 1 or 0) allocated to each primary color (red, green, and blue). A higher bit depth allows a greater number of colors to be represented. Modern displays typically have color depths of 8 or 10 bits |
| Color gamut | The range or spectrum of colors able to be represented on a display. Three common color gamuts are sRGB, CMYK, and adobe RGB |
| Subpixel | Subregion of a pixel, typically a single-color region of the pixel (red, green, or blue). Manipulating specific subpixels allows a display to render colors more accurately or to make images appear more vivid, muted, etc. |
| Lookup tables | Precalculated tables used to increase color depth and color accuracy above the native capabilities of the panel. These can also be generated from display calibration tools |
| Display format/aspect ratio | Width versus height dimensions of the display, typically expressed as a ratio (examples include 3:2, 4:3, 16:9, 16:10, 21:9, 32:9) |
| Display resolution | Resolution conveys the total number of pixels in the viewable area of the display, typically given as a two-dimensional, width by height, measurement. May be expressed a popular synonym. Example resolutions with synonyms include: 640 × 480 (VGA), 1920 × 1080 (HD), 2048 × 1080 (2K), 2560 × 1440 (WQHD), 3840 × 2160 or 4096 × 2160 (4K), 5120 × 2880 (5K), 7680 × 4320 (8K) |
| Physical image size (screen size) | Denotes the “size” of the viewable area on the display. Traditionally expressed as the diagonal measurement in inches (lower corner to opposite upper corner, typically should not include the bezels [borders] of the display) |
| ppi | Number of pixels present in one inch of surface. Analogous to the DPI used in paper printing |
| Pixel pitch | Denotes the distance between neighboring pixels, usually in millimeters. Pixel pitch is inversely related to display resolution, with a short pixel pitch typically associated with a “clearer” display (e.g., a 15” 4K display will have a shorter pixel pitch, and thus a higher ppi than a 55” 4K display) |
| Refresh rate | Number of times image is refreshed on the display per second, measured in Hz. Typically, with higher display refresh rates, motion will appear smoother (combined with response time, below). TV manufacturers may report out an “effective refresh rate” that uses proprietary technology plus the native refresh rate of the display to smooth motion even further |
| Response time | Measurement of how long it takes for a pixel on a display to change from one color to another (e.g., black to white) and is typically given in ms. Shorter response times correlate to less motion artifacts on a display (smoother motion overall) |
| Adaptive frame synchronization | Set of proprietary technologies that smooth out motion in graphically intensive applications, for example, in PC gaming |
| Inputs | The cable and port that allows graphical information from a computer or other device to be displayed on the display. HDMI and DisplayPort are currently the two most commonly used formats. Other options are USB, DVI, and VGA. Note that with each new iteration of digital input standards (e.g., HDMI v2.1), new cables and devices will be needed that support the standard |
| JND | Defined by the DICOM standard as “the luminance difference of a given target under given viewing conditions that the average human observer can just perceive” |
| Delta E2000 | A standardized formula proposed by the CIE for measuring the “distance” between two pixels in color space. Can be used for either gray-scale or color images |
MG: Medical grade, COTS: Consumer off the shelf, PG: Professional grade, CRT: Cathode ray tube, LCDs: Liquid crystal displays, CCFL: Cold-cathode fluorescent lamp, fL: Foot-Lamberts, RGB: Red-green-blue, sRGB: Standard RGB, CMYK: Cyan-magenta-yellow-black, VGA: Video graphics array, ppi: Pixel per inch, DPI: Dots per inch, HDMI: High-definition multimedia interface, USB: Universal serial bus, DVI: Digital visual interface, JND: Just noticeable difference, DICOM: Digital Imaging and Communications in Medicine, CIE: Commission on illumination, IPS: In-Plane-Switching, LED: Light-emitting diode, SI: International System of Units, HD: High Definition, WQHD: Wide Quad High Definition, PC: Personal Computer, TV: Television, A.k.a. picture element: Abbreviated form of ‘picture element