Geometry Nodes - Color Value as Float

Question

First, I'd like to provide some context. I have a low resolution 3d map. I made this map by subdividing a hexagon and applying a Displace modifier to it. A little color-ramp magic in the shader, and I have something that's conceivably usable for my purposes:

However, switching between the displacement texture and the rendering shader is inconvenient for painting changes onto the model. Before, it was the only way to do things, but now, I thought I'd try to use the Geometry Nodes system to displace my vertices with Vertex Paint as the input instead of a texture.

The problem is, the Displace node uses the texture's HSV value at each vertex directly, which is different from the color values visible in the spreadsheet editor. For instance, while a color with an HSV value of 0.0 has an internal value of 0.0, and a color with an HSV value of 1.0 has an internal value of 1.0, a color with an HSV value of 0.5 is stored with a value of 0.216 per the spreadsheet editor.

How do I convert the stored value into something approximating the HSV value?

Does this answer your question? How are color images used as input values in nodes? — Gorgious, Jul 05 '21 at 08:35
@Gorgious No, that question is 100% unrelated. Firstly, I'm not using images here. Second, the problem is that the value I'm expecting - the color luminance - is not the value reflected in the spreadsheet view. This difference is reflected in the vertex color itself, not post-conversion, so the conversion described in the linked question cannot be the problem. Furthermore, a lot of the nodes for working with colors simply don't exist in Geometry Nodes view, so I couldn't solve my problem the same way I might if I were working with Shader nodes. — Cameron Scoggins, Jul 08 '21 at 08:31
Could you maybe add a little more information then ? Post a screenshot of you spreadsheet editor and the expected behaviour, etc. — Gorgious, Jul 08 '21 at 08:54
I'm voting to leave this question open since OP can't use the linked answer. — Allen Simpson, Jul 08 '21 at 17:16
Also might be helpful: What happens when a vector is fed into a value slot of the add node? — Markus von Broady, Oct 18 '22 at 11:54

score 1 · Answer 1 · answered Sep 12 '22 at 12:51

In Blender 3.3+ you can solve this as follows:

In this version the node Separate Color offers you the possibility to choose between RGB, HSV or HSL.

The value for the vertex color is stored in the attribute Col, which you can query with the node Named Attribute.

Geometry Nodes - Color Value as Float

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