Glossary

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Matte black/gray

Black or gray object that reflects the same light intensity whatever the viewing angle or light source angle (not glossy).

Maze structures

Artifacts in images, with a maze shape, due to errors during demosaicing.

Metric

A metric is a lens or camera sensor image quality performance characteristic selected for analysis on DxOMark. There are three Metrics for scoring camera sensors (Color Depth, Dynamic Range, Low-Light ISO), and five Metrics for scoring lenses (Resolution, Distortion, Vignetting, Transmission, Chromatic Aberration).
Read more about Lens Metric definitions and Sensor Use Case definitions (Metrics and Use Cases are equivalent for sensors).

Mid-Light Score

The Mid-Light Score is the average performance of a lens with a camera body the different focal lengthfor a defined exposure conditions.

It is equivalent to the DxOMark Score except that it is based on mid-lighting conditions (5,000 Lux and 1/125s exposure time). Mid-Light Score makes a lot of sense when evaluating lenses with camera used in good lighting conditions: particularly appropriate for medium-format cameras used in studio environments.

Mid-tones

Exposure levels corresponding to medium gray levels on the sensor.

modulation transfer function (MTF)

Function describing the ratio between the amplitude of a pure frequency signal before and after a system as a function of the frequency.

Mpix

Megapixel, a million pixels.

Noise

Part of a measured signal which is different from the original signal. In an image, noise is especially visible in uniform areas

Noise covariance matrix

For a multichannel image, matrix giving the covariance of the noise in the different channels.

Noise removal

Algorithm aiming to retrieve the part of the signal directly related to the scene

Noise, dark

See Dark noise.

Noise, photonic

Random variations of the light perceived by the sensor due to the fact that photons are not emitted at a constant rate, but follow a random process (see Poisson process).

Noise, PRNU

Pixel response non-uniformity. Noise due to the inhomogeneity of pixels properties on the sensor.

Noise, thermal [electronic]

Also known as dark current noise. Part of the noise due to thermally generated free electrons. It is currently considered that thermal noise doubles for an increase of 8° of the ambient temperature. This noise is particularly visible in low-light.

Normalization

Action of changing numerical values with respect to a given reference in order to facilitate comparison between, for example, cameras having different sensor resolutions or sizes.

Normalized results

Results obtained after several mathematical transformations, used to easily compare systems with different characteristics, as camera resolution, pixel pitch, etc.

Optical axis

Axis of symmetry of an optical system, usually set at the center of the picture.

Optics

System for focusing light on a sensitive surface. See Lens.

Overexposure

An exposure that is too important, resulting in burnt highlights.

Peak Score (former score for lens with camera)

The term "Peak Score" is not used anymore on DxOMark. Ranking used to be provided using this Peak Score; now ranking is provided using the DxOMark Score.

Former definition of Peak Score (now renamed as Mid-Light Score and shown in the lens measurement page):

The Peak Score is the performance of a lens (with a camera body) for its best focal length and aperture combination. Therefore, it does not show how the lens behaves over its entire focal range. Other lens scores, such as Use Case and Optical Metric Scores, report average performances over the whole focal length and aperture ranges.

Also, the Peak Score is measured for defined exposure conditions corresponding to typical studio photography with 5,000 lux illumination and an exposure time of 1/125s.

Photography, silver halide

Photography using traditional film composed of chemical components and silver ions.

Photonic noise

Photons

The elemental particle of light. It has a zero mass, travels at light speed, and is characterized by its wavelength.

Photosites

Part of a sensor that receives photons. Each photosite corresponds to a pixel at the end of image processing.

Pixel

Picture element, the smallest element of a digital image.

Pixel pitch

Width of a pixel on a sensor, expressed usually in µm.

Pixel response non-uniformity (PRNU)

Pixel, hot, dead

A pixel (or photosite) whose response to light is very different from the mean response of the other pixels on the sensor. They produce small but very visible artifacts on an image.

Poisson process

Stochastic (or random) process modeling queuing phenomena. It is a good model of photons arrival on a sensor.

Portrait & Studio (use case)

Portrait & Studio corresponds to a photographic use where light and subjects are generally under the control of the photographer. Read more about Lens Use Cases and Sensor Use Cases definitions.

Portrait photography

Taking close-up photos of people, generally in a controlled environment (such as a studio).

Portrait Score

The Portrait Score is defined as the color depth performance and its unit is a number of bits.

A color depth of 22bits is excellent, differences below 1 bit are barely noticeable.

This score is named "Portrait" because generally what matters most when shooting portraits is to aim for the richest color rendition.

Read more about Portrait Score.

Prism effect

Dispersion of light: different wavelengths are refracted with a difference angle, like a rainbow.

Protocols, testing

The set of procedures used to measure characteristics of a camera.