I was inclined to believe that DIALux calculated the Reflection factor for texture materials by calculating the luminance value of each RGB pixel in the image file and averaging them to get the Reflection factor. In practice, I've found that there must be a different, preferred formula used in lighting simulation software- in both DIALux evo and AGi32, I have consistently gotten similar reflectance values from both software, however, the values are significantly lower than my calculated LRV.

For example, for the texture below, I get the following LRVs:

RGB/luminance average: 46%

DIALux evo (referred to as "Reflection factor"): 21%

AGi32 (referred to as "Average Reflectance"): 19%

Does anyone know the formula being used and why it would be preferred?