Resolution measurement at high noise levels
During the discussion within ISO TC42 working group 18 about the low light performance of digital cameras the question came up if at high visual noise levels, the MTF10 measurement value using a sinusoidal siemens star (ISO 12233) still represents the visual perception.
In order to find out if this is the case a TE42LL test chart as specified in ISO 19093 was captured with a Sony RX100 M6 at different ISO speed settings deactivating noise suppression as far as possible.
For the summary of the results the levels of ISO 100, ISO 3200 and ISO 12800 were selected out of a range of 8 levels.
Resulting measurement values:
| ISO Level | Visual Noise according to ISO 15739:2017 | Siemens SFR MTF10 [LP/PH] |
|---|---|---|
| 100 | 2.5 | 1476 (0,81 * Nyquist) |
| 3200 | 8.1 | 1369 (0,75 * Nyquist) |
| 12800 | 15.0 | 1278 (0,68 * Nyquist) |
The acceptable visual noise level that was determined in a psychophysical experiment last year is 5.3. This means that at ISO 12800 we are 3 times higher in noise than the acceptable limit.
From left to right the center of the center siemens star of the ISO 100, ISO 3200 and ISO 12800 image.
The red ring represents the Nyquist limit, the yellow ring represents 0.5 * Nyquist and the green ring represents the MTF10 measurement value.
The resulting siemens stars with the marked MTF10 measurement show very well that the Siemens SRF MTF10 measurement represents the visual threshold for resolution, also called limiting resolution, even in the presence of high noise levels.