Live hue mask, handling of neutral (grey) color

[NotMyFault]

The live hue mask is unable to filter for neutral colors (including them).
by convention, neutral colors show 0 saturation and hue zero (red), but LHM ignores 0 if saturation is zero.

you can use the color sampler to choose a neutral color from the underlying image. If you sample grey, the filter chooses red, but no neutrals get selected.

This behavior seems to be ok technically , maybe it should be explained in help.

and Affinity should explain how it is possible to choose grey pixels. 
I found no clear way:

• live masks cannot choose grey
• select sampled color chooses only limited luminosity range of grey, or non-grey colors if tolerance is large
• Select tonal range offers RGB only, no grey
• live hue mask excludes grey, even if you put nodes to the extreme. If you toggle „invert“, grey is chosen, but you cannot set the nodes all to the same position to choose only grey, other colors get always included.

has anybody found a better way to specifically select / filter pure grey hue?

[smadell]

What a challenge, @NotMyFault! One of the problems here is that grey is not a hue, but rather a saturation level. You need to use a "live saturation mask" and such a thing doesn't really exist inside AP. So…

Here's a macro that might work. It worked for me in limited testing (that is, about 3 minutes worth on a single photo). Also, it will only work inside of the newest beta version of Affinity Photo (v2.6 build 2984) because Serif added the ability to put "Mask to Below" in a macro. Basically, it creates a black and white layer based on saturation, puts a Live Luminosity Mask onto that layer, and then applies "Mask to Below" to put  the resulting mask into the selected layer. You probably need to start with the layer you want to apply the mask to already selected. But, after the macro runs, the Live Luminosity Mask is preserved and you can use it to vary the amount of grey you want to include in the mask.

The macro steps:

Deselect
Merge Visible
Name the Layer: Limit to Neutrals
Add a Procedural Texture
     for R, G, and B channels:   (Max(R,G,B)-Min(R,G,B))/Max(R,G,B)
Merge Down
Invert Layer
Add Luminosity Mask with preset Parameters
Select parent layer
Mask to Below

You can open the Live Luminosity Mask attached to the "Limit to Neutrals" layer and adjust the points to allow more or less of the original image be displayed. Let me know how this works, and if it answers your issue. The macro is attached (an .afmacro file, so import it into the Macro panel). Also, remember it will only work in the newest v2.6 beta (and, presumably, in versions thereafter).

Limit to Neutrals (v2.6 beta).afmacro