ISO 17957:2015 写真—デジタルカメラ—シェーディング測定 | ページ 2

Foreword

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

Introduction

One common type of image phenomenon seen in digital cameras is a systematic intensity variation across an image known as luminance shading. There are several causes of luminance shading in a digital camera: pixels having non-uniform sensitivity across a sensor array, illumination non-uniformity, lens shading, pixel geometry, and electronic non-uniformity. Characteristics of lens shading include symmetry about the optical sensor, uniformity across each colour plane, and variation as a function of cosⁿΘ. Luminance shading only affects intensity falloff.

Colour variations within the image can be induced by several factors, all of which will cause varying degrees of non-neutrality within an ideal uniform-gray exposure. Some of the primary factors include, (a) a mismatch between the CMOS micro-lens optical acceptance angle and the lens’ chief ray angle over the field of view, (b) spatially varying spectral transmittance differences from the infrared rejection filter (usually most significant at the cutoff wavelength), and (c) inherent spectral sensitivity differences across the array. Consistent, systematic variations can be reduced through correction via image processing, but there might remain residual colour variations.

The information that follows defines the recommended approach for creating a test scene to use for the evaluation of luminance shading and colour variations, as well as specifying the conditions for illumination and exposure. The currently proposed analysis approach to quantify the magnitude of colour variations is described. It is important to understand that this specification is related to the degree of colour variations that are apparent in the image, not the specific colour accuracy. Thus, an image that appeared pink but was uniformly pink over the entire image would be equivalent to a perfectly uniform gray field relative to this colour non-uniformity specification.

Some part of this International Standard is based on the work done by the Camera Phone Image Quality group (CPIQ) within the International Imaging Industry Association (I3A), now part of the Institute of Electrical and Electronics Engineers (IEEE), whose contribution is greatly acknowledged.

1 Scope

This International Standard defines a method for measuring shading for digital cameras (including camera phones). The method includes procedures for measuring colour and luminance signal components separately.

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

For the purposes of this document, the following terms and definitions apply.

Bibliography