Photon Transfer Curve (PTC)
Photon transfer curve: read, shot and PRNU noise regimes vs signal, their crossovers, conversion gain and dynamic range.
Total noise at full well
547.81 e⁻
273.91 DN
Temporal noise at full well
223.83 e⁻
after flat-field correction
Noise floor
5.01 DN
read 10.00 e⁻, quantization K/√12 = 0.58 e⁻
Read + quantization → shot
100 e⁻
S = σ_r² + K²/12, 50.2 DN
Shot → PRNU crossover
10000 e⁻
S = 1/PRNU², 5000 DN
Dynamic range
74.0 dB
full well 25000 DN over the noise floor
σ_total² = σ_read² + σ_q² + S + (PRNU·S)², all in e⁻; divide by K for DN. In the shot-noise regime σ²(DN) = S(DN)/K, so K = S/(σ²_diff/2 − σ_read²) from the offset-subtracted mean S of a frame-differenced (FPN-free) pair of flats (Janesick 2007, ch. 5).
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
σ_total² = σ_read² + σ_q² + S + (PRNU·S)² in e⁻, with σ_q = K/√12 and DN = e⁻/K. A linear sensor with a constant conversion gain, no dark charge and no DSNU. The temporal curve is what a frame-differenced or flat-fielded measurement sees.
- Janesick J. R. (2007). Photon Transfer: DN → λ. SPIE Press, ch. 5. σ_total² = σ_read² + σ_shot² + σ_FPN² with σ_FPN = P_N·S; PTC slopes 0, ½ and 1. doi:10.1117/3.725073
- EMVA Standard 1288, Release 3.1 (2016). Standard for Characterization of Image Sensors and Cameras, Eq. (11) and (48). Quantization noise σ_q² = 1/12 DN² and the total SNR with PRNU. emva.org