Resolution (photography)

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SilverFast Resolution Target USAF 1951 for measuring the resolution

As a resolution or resolving power in is called photography the ability of a lens , film or sensor , certain small structures to be able to play.



To determine the resolution, test recordings of line patterns are made, which are usually black and white or at least one color. For this purpose, a film is exposed with a line grid that has an ever decreasing distance (increasing spatial frequency ). A microdensitometer is used to measure how strong the distinctions are between the increasingly narrow lines.

The image resolution is determined by counting the still recognizable number of line intervals per millimeter. The determined value is also called the modulation transfer function. Only values ​​relating to light-dark contrasts are supplied. Therefore it cannot be deduced from this how good the resolution of multicolored structures is. For this it is necessary to use multicolored templates, such as white light interferograms or colored noise patterns .

Figure: Test pattern for determining the resolution of photographic lenses, films and sensors

Test pattern for determining the resolution of photographic lenses and films (1/3)


A distinction can still be perceived in the line grid, even if this distinction is fuzzy or has interference.

If the section of a Siemens star is reproduced, a different resolution pattern results for the digital image (center) than for the analog image (right).

For this reason, a tolerance limit is set for every measurement method. This defines the number of tolerable deviations (blurring, interference, contrast, ...).

Basic problem

  1. There are no binding standards for defining tolerable deviations (blurring, interference, contrast, etc.) when determining the resolution. Therefore, tests never produce identical test results.
  2. There is no suitable method for comparing materials with different basic structures (film and sensor). On the one hand, structural effects (for example moiré ) are not taken into account; on the other hand, the test result depends largely on the tolerance definition. An example:
  • Visibility of disturbances (grain): That would make the film the loser.
  • High contrast at the edge border: That would make the film the winner.

Analog resolving power

Selected color negative and reversal films:

  • The graininess is reported as an RMS value .
  • The resolving power was measured at various object contrasts (1.6: 1 and 1000: 1) and is given in lines per millimeter.
Film type Graininess ( RMS ) Resolving power in L / mm with object contrast
1.6: 1 1000: 1
Color reversal films
Fujichrome Velvia 100 F (100 ASA) 8th 80 160
Fujichrome Astia 100 F (100 ASA) 7th 60 140
Agfachrome RSX II 100 10 50 125
Ektachrome 100 prof. 11 50 100
Color negative films
Kodak Royal 25 80 200
Fujicolor Reala 100 4th 63 125
Kodak Ektapress Gold prof. 1600 11 40 80
Black and white negative films
Copex gigabit film 25 4th 90 900
Kodak TMAX 100 8th 63 200

Digital resolution

The resolution of digital camera sensors is also given in line pairs per millimeter. Since this resolution ultimately depends not only on the camera sensor, but also on the lens used, as is the case with film, this only results in reference values. At the beginning of digital photography, the number of pixels was also used for orientation about the resolution. This number is usually given in megapixels . The resolution actually achieved by the camera depends not only on the number of pixels, but also on the size of the image sensor and the hardware and software used by the camera to process the image signals. A measurement of the actually physically existing resolution can only be determined using a differentiated measurement method . There is still no uniform standard for such measurement methods, so that there are sometimes strong fluctuations in the measurement results.

Among other things, it must be taken into account that structural effects ( e.g. moiré ) can change the measurement result.

Different sections of one and the same photo: The middle section is overlaid by artifacts ( moiré ).
Without taking structural effects into account , the resolution cannot be clearly determined.

See also

Individual evidence

  1. Information according to the manufacturer's data sheets and typical comparison values ​​at