Calculating EV from lux

src/ev_calculator.py

@@ -0,0 +1,9 @@
+from math import log
+
+class EVCalculator:
+
+    def luxToEV(lux: float) -> float:
+        # Wikipedia (https://en.wikipedia.org/wiki/Exposure_value#EV_as_a_measure_of_luminance_and_illuminance)
+        # says E = 2.5 * (2^EV), so the inverse is EV = ln(2*E/5)/ln(2)
+        return log(2*lux/5, 2)
+

src/meson.build

@@ -31,6 +31,7 @@ lumos_sources = [
   'main.py',
   'window.py',
   'sensors_polling_timer.py',
+  'ev_calculator.py',
   'widgets/widgets_loader.py',
   'widgets/time_priority_page.py',
   'widgets/aperture_priority_page.py',

src/window.py

@@ -20,12 +20,14 @@
 from gi.repository import Adw
 from gi.repository import Gtk
 from .sensors_polling_timer import SensorsPollingTimer
+from .ev_calculator import EVCalculator
 
 @Gtk.Template(resource_path='/eu/ichibi/Lumos/window.ui')
 class LumosWindow(Adw.ApplicationWindow):
     __gtype_name__ = 'LumosWindow'
 
     lux_label = Gtk.Template.Child()
+    ev_label = Gtk.Template.Child()
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
@@ -34,11 +36,15 @@ class LumosWindow(Adw.ApplicationWindow):
         self.sensorsPollingTimer = SensorsPollingTimer(0.1, self.onSensorRead)
         self.sensorsPollingTimer.start()
 
-    def onSensorRead(self, value, unit):
+    def onSensorRead(self, value: float, unit: str):
         # Called when the light value changed
-	    print("Read {} {}".format(value, unit))
+        print("Read {} {}".format(value, unit))
 
-	    if self.lux_label:
+        if self.lux_label:
-	        self.lux_label.set_label("{:.0f} {}".format(value, unit))
+            self.lux_label.set_label("{:.0f} {}".format(value, unit))
 
+        # Convert lux to EV
+        ev = EVCalculator.luxToEV(value)
+        if self.ev_label:
+            self.ev_label.set_label("{:.1f} EV".format(ev))
 

src/window.ui

@@ -96,6 +96,14 @@
                             </style>
                           </object>
                         </child>
+                        <child>
+                          <object class="GtkLabel" id="ev_label">
+                            <property name="label" translatable="no">XXX EV</property>
+                            <style>
+                              <class name="title-1"/>
+                            </style>
+                          </object>"
+                        </child>
                       </object>