ISO 17850:2015
(Main)Photography — Digital cameras — Geometric distortion (GD) measurements
Photography — Digital cameras — Geometric distortion (GD) measurements
ISO 17850:2015 specifies a protocol to measure geometric distortion of a digital camera. It is applicable to the measurement of digital cameras including camera phones.
Photographie — Caméras numériques — Mesurages de distorsion géométrique (DG)
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 17850
First edition
2015-07-01
Photography — Digital cameras
— Geometric distortion (GD)
measurements
Photographie — Caméras numériques — Mesurages de distorsion
géométrique (DG)
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement methods . 2
4.1 General . 2
4.2 Local geometric distortion . 3
4.3 Line geometric distortion . 3
5 Requirements . 4
5.1 Apparatus and hardware . 4
5.2 Lighting . 4
5.3 Dot chart . 5
5.3.1 Design and characteristics. 5
5.3.2 Requirement for the chart planarity . 6
5.4 Grid chart . 7
5.4.1 Design and characteristics. 7
5.5 Image/camera settings . 8
5.5.1 General. 8
5.5.2 Basic settings and influencing factors . 8
5.5.3 Specific test procedures . 8
5.5.4 Positioning of the camera . 8
5.5.5 Exposure, white balance, and focus . 9
6 Determination of geometric distortion .10
6.1 Local geometric distortion .10
6.1.1 Numerical definition . .10
6.1.2 Outline of the practical algorithm .10
6.2 Line geometric distortion .11
6.2.1 Horizontal line distortion .11
6.2.2 Vertical line distortion .12
6.2.3 Total line distortion .12
7 Presentation of results .13
7.1 General .13
7.2 Local geometric distortion .13
7.3 Line geometric distortion .14
Annex A (informative) Illustrative example and validation .15
Annex B (informative) Extracting the dots from the target .17
Annex C (informative) Dot centre validation .25
Annex D (informative) Grid sort .30
Annex E (informative) Example of subjective evaluation .40
Bibliography .48
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 42, Photography.
iv © ISO 2015 – All rights reserved
Introduction
A digital still camera (DSC) typically employs a taking lens that is a rotationally symmetric optical
system. Generally, the function of rotationally symmetric optical systems is to form an image that is
geometrically similar to the object except some particular systems, such as fish-eye lenses and eyepieces,
where this condition is deliberately not maintained. This function is accomplished ideally according to
the geometry of perspective projection. Departures from the ideal image geometry are called distortion.
The distortion is a position-dependent quantity which generally has a vectorial character. In a given
image plane (which may also lie at infinity), this vector, representing the difference between theoretical
and real image position, has a radial and a tangential component. In optical systems, the tangential
component is basically conditioned by imperfect rotational symmetry. The systems manufactured in
accordance with the present state of the art have a negligible tangential distortion.
Geometric distortion (GD) of DSCs is mainly caused by the variation of magnification in the image field of
the camera lens. The most well-known effect of distortion is that straight lines appear curved. Generally
speaking, the proportions between objects are not preserved in a distorted image, which can be very
unpleasant for some natural scenes, architecture, or portraits. Distortion is fully described by a 2D map,
giving the displacement from a point in an ideal undistorted image to the point in the actual distorted
image. The image centre is usually assumed to be undistorted; the magnification factor at this position
actually defines the focal distance.
Different types of distortion are usually characterized by how the magnification radially varies within
the image field. Barrel and pincushion are the most usual types of distortion for which magnification
is respectively monotonously decreasing and monotonously increasing when moving along from the
centre to the border of the image field. Other types which cannot be categorized into above two types
are usually called wave distortion.
a) Barrel (or negative) distortion
b) Pincushion (or positive) distortion
NOTE The magnification is decreasing for barrel distortion and increasing for pincushion.
Figure 1 — Two main types of distortions
ISO 9039 defines methods to measure a lens that is separated from a camera. On the other hand, this
International Standard was developed and defines methods to measure the total image distortion of a
camera including a lens and signal processing.
This International Standard is based on both Reference [3] prepared by the Camera Phone Image Quality
(CPIQ) group within the International Imaging Industry Association (I3A) and Reference [4] prepared
by Camera and Imaging Products Association (CIPA).
vi © ISO 2015 – All rights reserved
INTERNATIONAL STANDARD ISO 17850:2015(E)
Photography — Digital cameras — Geometric distortion
(GD) measurements
1 Scope
This International Standard 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
...
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