ISO 18844:2017
(Main)Photography — Digital cameras — Image flare measurement
Photography — Digital cameras — Image flare measurement
ISO 18844:2017 specifies the definition of image flare for digital cameras, test patterns, measurement conditions, and methods, so as to enable the comparison of the results of measurement. The methods of measurement are designed to enable the assessment of the performance of digital cameras by using image data output by the digital cameras. ISO 18844:2017 does not specify the aim values or the allowable range of value for the image flare.
Photographie — Caméras numériques — Mesurage de l'éclat d'image
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 18844
First edition
2017-05
Photography — Digital cameras —
Image flare measurement
Photographie — Caméras numériques — Mesurage de l’éclat d’image
Reference number
ISO 18844:2017(E)
©
ISO 2017
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ISO 18844:2017(E)
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© ISO 2017, Published in Switzerland
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ISO 18844:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement chart and method . 2
4.1 Conditions of shooting . 2
4.1.1 Arrangement of measuring equipment . 2
4.1.2 Conditions of shooting . 3
4.2 Charts . 3
4.2.1 General. 3
4.2.2 Charts for single spot measurement . 4
4.2.3 Charts for multiple spot measurement . 4
4.3 Measurement procedure . 5
4.3.1 General. 5
4.3.2 Calculation of luma and luminance. 5
4.3.3 Areas used for calculation of luma and luminance . 6
4.3.4 Measurement types . 7
5 Presentation of results . 9
Annex A (informative) Examples of reporting .11
Bibliography .12
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ISO 18844:2017(E)
Foreword
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This document was prepared by Technical Committee ISO/TC 42, Photography.
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ISO 18844:2017(E)
Introduction
When images are produced by a digital camera, the camera captures not only the light from the scene
but also stray, unwanted light (flare) that can reduce contrast in the image. Generally, the processing
applied to the image will compensate for normal amounts of flare light, resulting in improved image
quality. However, flare light can be quite variable, and image processing algorithms are not always
successful at removing it. Poor or excessive flare removal processing can reduce the quality of the final
image. For example, subtraction of the average flare across the image could result in over-subtraction
of the flare in dark areas, resulting in loss of shadow detail. In evaluating digital cameras, it is therefore
useful to measure the signal from the flare light remaining in processed images. This remaining flare
signal is called “image flare.”
Image flare in digital cameras is caused not only by lenses but also by camera bodies and image sensors,
and is affected by image processing. Measurements of image flare include all contributing factors:
the optical system, camera body, image sensor, and image processing. ISO 9358 specifies methods
of measuring “veiling glare,” the flare from lens systems, but it is not intended to be applied for the
measurement of image flare. This document specifies a method to measure image flare using the image
data output by digital cameras.
A standard method is needed in part because of the nature of image flare. It can vary both locally and
from image to image depending on all the factors mentioned above. While it is possible to measure
image flare at different positions in different images, the variability of image flare makes it difficult to
compare such measurements out of context. This document provides a standard method for measuring
image flare which can be useful for cross comparison.
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INTERNATIONAL STANDARD ISO 18844:2017(E)
Photography — Digital cameras — Image flare
measurement
1 Scope
This document specifies the definition of image flare for digital cameras, test patterns, measurement
conditions, and methods, so as to enable the comparison of the results of measurement.
The methods of measurement are designed to enable the assessment of the performance of digital
cameras by using image data output by the digital cameras.
This document does not specify the aim values or the allowable range of value for the image flare.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 61966-2-1, Multimedia systems and equipment —Colour measurement and management — Part 2-1:
Default RGB colour space — sRGB
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
image flare
unwanted increase in signal in a processed image output by a digital camera resulting from light
detected by an image sensor that does not emanate from a corresponding subject point
Note 1 to entry: Image flare is measured for a camera system. The camera system includes lenses, camera body,
image sensor, and image processing used for the measurement. The following four are common with regard to
light detection: i) internal multiple reflections, scattering or diffraction of optics (including lens surfaces, filter
surfaces, or sensors), ii) light diffusion at lens barrel, body, or edge of lens, iii) leaking of light, and iv) the optical
system as measured by point spread function including spherical and chromatic aberrations. Differentiation
between these four might be difficult once an image is captured, but it is more appropriate to isolate the last one
with regard to the system resolution. Thus, care should be taken to minimize point spread function contribution
in the measurement of image flare. Image flare also includes the effects of image processing. Even if the same
camera is used to capture RAW image data, different image flare values might be measured if different image
processing algorithms are applied. This is an intended result because the measurement of image flare includes
all contributing factors of lenses, camera body, image sensor, and image processing.
Note 2 to entry: “Image flare” was defined in ISO 3664:2000 in another context, but it was deleted in
ISO 3664:2009.
Note 3 to entry: “Image flare” is defined in ISO 12231:2012 but without any source standards. The definition is
the same statement as in ISO 3664:2000. ISO 3664:2000 was replaced by ISO 3664:2009 and this does not include
the definition of “image flare.”
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ISO 18844:2017(E)
4 Measurement chart and method
4.1 Conditions of shooting
Each test chart shall be specified together with the lighting conditions such as illuminance, luminance,
and colour temperature of illumination.
4.1.1 Arrangement of measuring equipment
4.1.1.1 Reflection-type test chart
The arrangement of the measuring equipment for a reflection-type test chart shall be set up as shown
in Figure 1. The light source(s) should be positioned to provide uniform illumination and produce no
glare or specular reflections from the target.
Matte black wall or black surround
Test chart
Distance is
adjusted to
frame
Lamp
Lamp
the test chart
Bafles to prevent direct
Digital
illumination of the
camera
camera lens by the lamps
Figure 1 — Arrangement of measuring equipment for reflection-type test chart
4.1.1.2 Transparent-type test chart
The arrangement of the measuring equipment for a transparent-type test chart shall be set up as shown
in Figure 2.
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ISO 18844:2017(E)
Matte black wall or black surround
Lighting box
Test chart
Distance is adjusted
to frame the test chart
Digital still
camera
Figure 2 — Arrangement of measuring equipment for transparent-type test chart
4.1.2 Conditions of shooting
Unless otherwise stated, the conditions of shooting are as follows.
a) Illuminance of illumination of a reflection-type test chart should be 1 000 lx to 2 000 lx.
2 2
b) Luminance of transparent-type lighting box should be 318 cd/m to 637 cd/m .
c) Total non-uniformity of lighting and test chart shall be <5 %; (|Max-Ave|/Ave <0,05 and |Min-Ave|/
Ave <0,05).
d) Average outdoor daylight illuminant shall be used. The CCT (correlated colour temperature) of the
illuminant shall be 5 700 K ± 1 000 K.
The illuminance should be measured using an illuminance meter (without cosine correction) positioned
at the centre of the test chart, pointing the receptor in the direction of the digital camera to be measured.
Illumination from the outside of the chart can increase the measured image flare value, and should
therefore be avoided for this measurement.
When shooting, lower camera sensitivity setting should be used in order to avoid the effect of noise.
4.2 Charts
4.2.1 General
The size of the charts shall exceed the field of view of the camera lens by (41 ± 2) %, in both the vertical
and horizontal directions.
Chart 1 has a white surface, and the field of view shall be specified by a black rectangle whose thickness
is one five-hundredth of the vertical length (shorter side) of the rectangle. The measurement areas shall
be specified by black areas drawn in the rectangle. Several black areas may be arranged diagonally, but
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ISO 18844:2017(E)
the total of th
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