ISO 15739:2023 写真撮影 — 電子静止画撮影 — 騒音測定 | ページ 6

3.1

camera opto-electronic conversion function

camera OECF

relationship between the input scene log luminances and the output pixel values for an opto-electronic digital capture system

Note 1 to entry: The unit of luminance (L) is cd/m². Log luminance is dimensionless, expressed as log₁₀ (L/L₀) ここで, L₀ = 1 cd/m².

3.2

clipping value

pixel value that remains constant for further increases in exposure (highlight clipping value) or for further decreases in exposure (dark clipping value)

3.3

digital still camera

DSC

camera that produces a digital still image from the digitized output of a solid-state photo sensor and records the digital still image using a digital memory, such as a removable memory card

3.4

DSC dynamic range

ratio of the input signal (luminance or exposure) saturation level to the minimum input signal level that can be captured with a signal-to-temporal noise ratio of at least 1

3.5

exposure time

total time period during which the photo sensor is able to integrate the light from the scene to form an image

3.6

focal plane opto-electronic conversion function

focal plane OECF

relationship between the input focal plane log exposures and the output pixel values for an opto-electronic digital image capture system

Note 1 to entry: The unit of exposure (H) is lx⋅s. Log exposure is dimensionless, expressed as log₁₀ (H/H₀) ここで, H₀ = 1 lx⋅s.

3.7

image sensor

electronic device which converts incident electromagnetic radiation into an electronic signal

Note 1 to entry: A complementary metal oxide semiconductor (CMOS) image sensor and a charge coupled device (CCD) image sensor are examples of image sensors.

3.8

noise

unwanted variations in the response of an imaging system

3.8.1

total noise

all the unwanted variations, consisting of fixed pattern noise (3.8.2) and temporal noise (3.8.3) , of the values in the image signals captured by a single exposure

Note 1 to entry: The procedure in this document for calculating the total noise requires multiple frames.

3.8.2

fixed pattern noise

FPN

unwanted spatial pixel variations of the values in the image signals which remain constant from frame to frame given the same illumination, aperture value, integration time, and ISO sensitivity setting

Note 1 to entry: Most fixed pattern noise (FPN) varies in digital number with sensor gain and ISO sensitivity setting and cannot, therefore, be considered static relative to exposure. There are three classes of fixed pattern noise, (1) static with integration time, for example, pixel FPN, column FPN and row FPN, (2) varies with integration time, for example dark current FPN, but static from frame to frame, and (3) signal dependent FPN such as photo response non-uniformity (PRNU), but still static from frame to frame.

Note 2 to entry: PRNU is a pixel to pixel gain mismatch. It is normally expressed as a percentage of signal because it is a gain error. It is static from frame to frame and, thus, contributes to fixed pattern noise but its magnitude is a function of signal level. It is, therefore, considered as a signal dependent FPN.

3.8.3

temporally varying noise

temporal noise

unwanted variation in the values of the image signals that changes from frame to frame due to sensor dark current shot noise, photon shot noise, analogue processing, and quantization

3.9

noise spectrum

curve or equation which expresses the image noise as a function of two-dimensional image spatial frequencies

3.10

saturation

condition where the camera output signal reaches the maximum valid (not clipped or bloomed) value

3.10.1

exposure saturation

minimum focal plane exposure that produces the maximum valid (not clipped or bloomed) camera output signal

Note 1 to entry: The exposure saturation is expressed in lux-seconds (lx⋅s).

3.10.2

luminance saturation

minimum scene luminance that produces the maximum valid (not clipped or bloomed) camera output signal

Note 1 to entry: The luminance saturation is expressed in candelas per square meter (cd/m²).

Note 2 to entry: The luminance saturation is determined for a fixed exposure setting of the camera under test.

3.11

signal-to-noise ratio

ratio of the input signal (luminance or exposure) level to the root mean square (rms) noise level, at a particular signal level

Note 1 to entry: In this document, the output pixel value is converted to an input signal level by applying the inverse OECF. The average of the input signal levels corresponds to the scene luminance (focal plane exposure) value when capturing an image. Unwanted variations exist in the converted input signal level that are centred about its average. This variation in input signal level is noise and is measured as the rms value.

Note 2 to entry: This is typically expressed as a graph or table showing the signal-to-noise ratio versus input signal level for the full range of input signal levels.

3.12

test density

spectrally non-selective transmittance filter used to reduce an input luminance to a predefined ratio of the unfiltered luminance