= Optical contrast in decibels
{title2=$L=10\log_{10}C$}
\b[Optical contrast in decibels] expresses a specified ratio logarithmically. For peak-to-local <radiant power> contrast $C=P_{\max}/P(t)>0$,
$$
L=10\log_{10}C,\qquad C=10^{L/10}.
$$
The inverse convention $r=P(t)/P_{\max}$ gives $10\log_{10}r=-L$. State the convention and the time of the weak feature. A $60\,\mathrm{dB}$ peak-to-feature contrast means one million to one in power, not in field amplitude.
An original readout example uses a linear <photodetector> whose baseline-corrected output is proportional to optical power. A main reading of $0.80\,\mathrm V$ and weak-feature reading of $80\,\mathrm{\mu V}$ imply $C=10^4$ and $L=40\,\mathrm{dB}$. Applying $20\log_{10}$ to those readings would incorrectly report $80\,\mathrm{dB}$: the electrical signal represents power, not optical <wave amplitude>.
If instead a measurement is proportional to an optical field amplitude $A$, with the same impedance and spatial normalization for both fields, power is proportional to $|A|^2$. Then
$$
10\log_{10}\frac{|A_1|^2}{|A_2|^2}
=20\log_{10}\frac{|A_1|}{|A_2|}.
$$
A field-amplitude ratio of $100$ and a power ratio of $10^4$ therefore express the same $40\,\mathrm{dB}$ contrast. The correct multiplier follows the measurement model, not whether the readout unit happens to be volts.
Contrast does not specify <pedestal energy fraction>, <optical prepulse> duration or delay coverage. The Sequoia primary sheet specifies dynamic range, scan range and optical temporal resolution separately.<Sequoia temporal contrast measurement by Amplitude>[January2024 technical sheet, PDFp2, Specifications]{ref} A signal beneath a known measurement floor supports a contrast bound within that window; subtracting an uncertain background does not establish unlimited contrast.
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