Here is a new list of names to which to attach to the scale of 1-256 in greyscale. Here is a link to an awesome paper by Kanan and Cottrell where they speak of converting RGB to greyscale images.

Gleam Intensity Luma, Luminance, Lightness Luster Value Brightness Decolorize — processes which are not the same by any stretch and about which I know little. In the case of surfactant protein D AFM images, knowledge of the types of conversions and how best to preserve the original image in conversion would have been (i may still look i up) nice to understand.
looks like Value and Luster and Decolorize are conversion ways that preserve the RGB values in a way that might be preferable for looking at AFM images as they are changed to greyscale. Photoshop used similar conversion of the Ishihara 29 in their “discard color” option (this is an old version of Photoshop so maybe new versions allow for the type of greyscale conversion to be selected).
Here is their chart: and below is my use of CorelDRAW and one Ishihara plate (test for color blindness with the 29 in it) with conversion to greyscale with and without autocontrast.