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CTnoise.add: use MATLAB's default photon count and clamp non-positive readings #781

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Merged
AnderBiguri merged 1 commit into from
Sep 29, 2026
Merged

CTnoise.add: use MATLAB's default photon count and clamp non-positive readings #781

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7 changes: 6 additions & 1 deletion Python/tigre/utilities/CTnoise.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,10 @@ def add(projections, Gaussian=None, Poisson=None):
"Poisson value should be an scalar, is " + str(type(Poisson)) + " instead."
)
else:
Poisson = np.ceil(np.log2(np.max(np.abs(projections)))) # nextpow2
# same default photon count as MATLAB's addCTnoise
Poisson = 60000
if np.max(projections) > Poisson:
Poisson = np.max(projections) / 5
if Gaussian is not None:
if not isinstance(Gaussian, np.ndarray):
raise ValueError(
Expand All @@ -23,6 +26,8 @@ def add(projections, Gaussian=None, Poisson=None):
projections = Poisson * np.exp(-projections / max_proj)

projections = RNG.add_noise(projections, Gaussian[0], Gaussian[1])
# the Gaussian term can push a reading to zero or below, where the log is not finite
projections[projections <= 0] = 1e-6

projections = -np.log(projections / Poisson) * max_proj
projections = np.float32(projections)
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