ISO 17850-2015 pdf free.Photography一Digital cameras – Geometric distortion (GD) measurements.
ISO 17850 specifies a protocol to measure geometric distortion of a digital camera. It is applicable to the measurement of digital cameras including camera phones.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic conversion functions (OECFs).
IEC 61146-1, Video cameras (PAL/SECAM/NTSC) — Methods of measurement — Part 1: Non-broadcast single-sensor cameras
EBU Tech3249, Measurement and analysis of the performance offilm and television camera lenses
3 Terms and definitions
3.1 geometric distortion GD <of DSC> displacement from the ideal shape of a subject (lying on a plane parallel to the image plane) in
the recorded image
Note I to entry: Geometric distortion basically derives from variation of lateral magnification in the image field of a camera lens and results in straight lines being rendered as curves. There are other factors to induce geometric distortion, for example, rotational asymmetricity of a camera lens or position shift processing in a camera imaging process.
3.2 image height
3.2.1 Image height <of DSC> distance between an image point and the centre of the image area or its relative expression which is the value normalized by one half of the diagonal of the image area
Note ito entry: This is an extension of the definition In ISO 9039 which is a measurement for optical systems.
3.2.2 actual Image height <of DSC> image height of an actual recorded image point in the recorded image area
4 Measurement methods
4.1 General
As defined in 3..1. geometric distortion basically derives from the variation of magnification in the image field. If this phenomenon occurs in an image, it means that a regular structure in an object does not appear to be regular in the image taken with the camera. There are two ways defined in this International Standard to quantify the amount of geometric distortion in an image. Both have their pros and cons.
4.2 Local geometric distortion
Geometric distortion can be measured on a white chart containing black dots at the position of a regular grid or on a grid chart formed by straight lines. The local geometric distortion method analyses the grid formed by the test chart in the centre of the image and calculates the ideal positions of the structure based on the measured distances. After that, it analyses the rest of the image and locates all actual positions of the grid. The distance between the ideal position and the actual position is the geometric distortion at that location in the image.
The distance between the two positions can be plotted as a function over the distance to the image centre. This curve indicates the variation of image magnification versus the actual image height, which is an expression of the geometric distortion called local geometric distortion. In order to limit the result to a single value that might get reported with the cameras specifications, the maximum (peak to peak) value shall be reported.
The manufacturing tolerances, such as lens tilt or off-centring, can result in a non-rotationally symmetric GD behaviour, lithe system is not rotationally symmetric, it can lead to increased distortion levels in the image corners. In this case, the measured geometric distortion is correct for the camera under test but might not represent a standard camera of the tested model.
4.3 Line geometric distortion
The principle of line geometric distortion is to measure the bending of a straight horizontal or vertical line at defined distances from the image centre and to report the maximum of the measured bending. This bending is preferably measured on a chart with a regular line grid.ISO 17850 pdf free download.
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