Using the standard shader, how to get the current emission brigthness in code?

Hey, Jonathan!

Thanks for the insight. I created a small test script to test your explanation but I found it to be almost right. The problem with your solution is that by picking the highest component and dividing all of them by that one we normalize the HDR color back to a non-HDR state but the normalized color can differ from the original color if the original color brightness is less than 1.

Hard to explain in words, here it is an example:

 An example that work:
 Original Color: (0.0, 0.5, 1.0)  // Original color brightness is 1 (one of the components must be equal to one)
 Brightness: 6.35 // Any value greater that 1 to generate an HDR color.
 Resulting HDR Color: (0.0, 3.175, 6.350) // Original Color * Brightness
 Biggest Component: 6.350
 Restored Color: (0.0, 0.5, 0.1) // Resulting HDR Color / Biggest Component

 An example that doesn't work:
 Original Color: (1.161, 0.422, 0.684) // Original color brightness is 0.684
 Brightness: 6.35 // Any value greater that 1 to generate an HDR color.
 Resulting HDR Color: (1.022, 2.682, 4.342) // Original Color * Brightness
 Biggest Component: 4.342
 Restored Color: (0.235, 0.618, 1) // Resulting HDR Color / Biggest Component

Here, take the script that I created to test this. The problem became easy to see when you set the brightness value to something greater that 1 and play with the original color:

 [ExecuteInEdit$$anonymous$$ode]
 public class ColorTest : $$anonymous$$onoBehaviour
 {
     [ColorUsage(true, true, 0, 8f, 0.125f, 3f)]
     public Color originalColor = new Color(0.1f, 0.2f, 0.3f, 1f);
     public float brightness = 3;

     [Header("Calculated (don't change manually):")]
     [ColorUsage(true, true, 0, 8f, 0.125f, 3f)]
     public Color multipliedColor;
     public float biggestValue;
     [ColorUsage(true, true, 0, 8f, 0.125f, 3f)]
     public Color restoredColor;
 
     void Update()
     {
         multipliedColor = originalColor * brightness;

         biggestValue = multipliedColor.r;
         if (multipliedColor.g > biggestValue) biggestValue = multipliedColor.g;
         if (multipliedColor.b > biggestValue) biggestValue = multipliedColor.b;

         if (biggestValue > 1f)
         {
             restoredColor =
                 new Color(
                     multipliedColor.r / biggestValue,
                     multipliedColor.g / biggestValue,
                     multipliedColor.b / biggestValue
                     );
         }
         else
         {
             restoredColor = multipliedColor;
         }

         Debug.Log("---");
         Debug.LogFormat("originalColor: {0}", originalColor);
         Debug.LogFormat("hdrColor: {0}", multipliedColor);
         Debug.LogFormat("biggestValue: {0}", biggestValue);
         Debug.LogFormat("restoredColor: {0}", restoredColor);
     }
 }