AS ISO 12232:2019 pdf download.Photography—Digital still cameras—Determination of exposure index,ISO speed ratings, standard output sensitivity, and recommended exposure index.
5 Test conditions
5.1 General
The following measurement conditions should be used as nominal conditions when determining the ISO speed ratings, SOS, and RE! values of a DSC. If it is not possible or not appropriate to use these nominal operating conditions, the actual operating conditions shall be listed along with the reported values.
5.2 Illumination
The reported values shall indicate whether illumination approximating the ISO 7589 daylight or studio tungsten illuminant was used. ISO 7589 describes the procedures for determining if the illumination used in a specific speed rating determination test is an acceptable match to the daylight and studio tungsten illuminants. Also, the spectral power distribution of the illumination used should be reasonably similar to that of the ISO 7589 daylight or studio tungsten reference illuminant.
5.2.1 Daylight reference illuminant
For daylight measurements without the camera lens, the ISO sensitometric daylight illuminant given in ISO 7589:2002, Table 1, shall be used. This illuminant is defined as the product of the spectral power distribution of CIE colorimetric standard illuminant D55 and the spectral transmittance of the International Standard camera lens. For measurements with the camera lens in place, the spectral radiance characteristics of the light used for the measurement should be equivalent to the daylight ISO standard source provided in the second column of ISO 7589:2002, Table 1. In order to apply the ISO SD! (spectral distribution index) criterion, the spectral radiance of the light shall be measured and then multiplied by the relative spectral transmittance of the ISO standard lens, which is also described in ISO 7589, prior to multiplying by the weighted spectral sensitivities.
5.2.2 Tungsten reference illuminant
For tungsten measurements without the camera lens, the ISO sensitometric studio tungsten illuminant
given in Iso 7589:2002, Table 2, shall be used. This illuminant is defined as the product of the average spectral power distribution of experimentally measured sources having a colour temperature of approximately 3 050 K and the spectral transmittance of the International Standard camera lens. For measurements with the camera lens in place, the spectral radiance characteristics of the light used for the measurement should be equivalent to the tungsten ISO standard source provided in the second column of ISO 7589:2002, Table 2. In order to apply the ISO SDI (spectral distribution index) criterion, the spectral radiance of the light shall be measured and then multiplied by the relative spectral transmittance of the ISO standard lens, which is also described in ISO 7589, prior to multiplying by the weighted spectral sensitivities.
5.3 Temperature and relative humidity
The ambient temperature during the acquisition of the test data shall be (23 ± 2) °C and the relative
humidity should be (50 ± 20) %.
5.4 White balance
For a colour camera, the camera white balance should be adjusted, if possible, to provide proper white balance (equal RGB signal levels) for the illumination light source, as specified in ISO 14524.
5.5 Infrared (IR) blocking filter
If required, an infrared (IR) blocking filter shall be used as specified in ISO 14524.
5.6 Photosite integration time
The photosite integration time should not be longer than 1/30 s.
5.7 Compression
If the DSC includes any form of lossy compression, the compression shall be disabled, if possible, during the determination of U(DH) or G(DL) in Clause 6. If it is not possible to disable the camera compression, the noise-based values cannot be properly determined, and shall not be reported.
5.8 Other DSC user settings
All other camera controls (e.g. sharpness, contrast) shall be set to the factory default settings. Additional, optional, measurements can also be made using camera control settings that are not the factory default settings. However, the reporting of such optional measurements shall be done in a manner that does not cause confusion with the primary measurements made using the factory default settings.
6 Determination of ISO speed and ISO speed latitude
6.1 General
With appropriate electrical or digital gain, a DSC can provide an appropriate DSC image signal level for a range of sensor exposure levels. The maximum exposure level is just below the exposure level where typical picture highlights will be clipped as a result of saturating the image sensor’s signal capacity or reaching the camera signal processing’s maximum signal level. The minimum exposure level relates to the amount of noise that can be tolerated in the image. These situations lead to two different types of speed value calculations: those based on saturation exposure, and those based on mid-tone noise characteristics, If the DSC provides an adequate dynamic range, the ISO speed is determined using a noise-based calculation and the saturation-based calculation is used to determine the camera’s overexposure latitude. A second noise-based calculation is used to determine the camera’s underexposure latitude.
For some types of DSCs, such as those employing lossy compression methods, it is not possible to correctly determine the mid-tone noise characteristics. In such cases, the ISO speed of the camera is determined using the saturation-based calculation, and the ISO speed latitude values are not reported. In other cases, the noise-based values may be lower than the saturation-based values, in which case the saturation based value is reported.
ISO speed and ISO speed latitude values may be reported for either scene-referred or output-referred images. ISO speed and ISO speed latitude values shall not be reported for raw images, however, because with raw images processing that affects the values has not been performed.AS ISO 12232 pdf download.