Blender - Alpha is Luminance equivalent Coming from Maya and Arnold there is a very simple selection box in the file read node (image texture equivalent) called Alpha is Luminance which allows to use the luminosity in the RGB values of a file to drive the alpha channel. Is there an equivalent function in Blender 2.8 and Cycles?
Cycles performs this conversion automatically when a color channel (yellow socket) is a connected to a float/scalar channel (grey socket). As a result, there is no need to have an option on image textures to replace the alpha channel with the merged color channels. You can simply plug the color output directly into the float channel and it will use the luminosity.