Add an auto exposurer.

AutoExposure.py

@@ -0,0 +1,41 @@
+import numpy as np
+from math import log2, pow
+
+class AutoExposurer:
+    def __init__(self, maxGain, maxExp):
+        self.maxGain = maxGain
+        self.maxExp = maxExp
+        self.skipFrames = 5  # the first skipFrames frames will be skipped
+        self.gainStep = 50 if maxGain > 400 else 10
+        self.targetBrightnessLow = 100
+        self.targetBrightnessHigh = 160
+        self.targetBrightness = (self.targetBrightnessHigh + self.targetBrightnessLow) / 2
+
+    # Returns (changed, newGain, newExp, med)
+    def adjustExp(self, gain, exp, img):
+        if self.skipFrames > 0:
+            self.skipFrames -= 1
+            return (False, None, None, 100)
+        med = np.median(img)
+        if self.targetBrightnessLow < med < self.targetBrightnessHigh:
+            return (False, None, None, med)
+        if med > self.targetBrightnessHigh:
+            ratio = med / self.targetBrightness # > 1.0
+            # Need to reduce exposure. Reduce gain if possible.
+            gainDelta = self.gainStep * log2(ratio)
+            if exp >= gainDelta:
+                return (True, int(gain - gainDelta), int(exp), med)
+            gainDeltaFulfilled = pow(2, gain)
+            exposureDelta = ratio / gainDeltaFulfilled
+            # We don't have a min epxosure
+            return (True, 0, int(exp / exposureDelta), med)
+        if med < self.targetBrightnessLow:
+            ratio = self.targetBrightness / med
+            # Need to bump exposure. Increase exposure if possible
+            if exp * ratio < self.maxExp:
+                return (True, gain, int(exp * ratio), med)
+            expDeltaFulfilled = self.maxExp / exp
+            gainDelta = self.gainStep * log2(ratio / expDeltaFulfilled)
+            newGain = min(self.maxGain, gainDelta + gain)
+            return (True, int(newGain), int(self.maxExp), med)
+