ISO 17850:2015 写真—デジタルカメラ—幾何学的歪み（GD）測定 | ページ 2

Foreword

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The committee responsible for this document is ISO/TC 42, Photography.

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.

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).

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.

3 Terms and definitions

Bibliography