[BUG] `method` parameter in "plot_RGB_chromaticities_in_chromaticity_diagram" definition does not work.

[cripplePX]

Description

No matter which one I choose, ice 1931 will be used by default

Code for Reproduction

Exception Message

Environment Information

[KelSolaar]

Hi @cripplePX,

Can you please share your code, it is not very clear what you are trying to achieve here.

Cheers,

Thomas

[Jackchou00]

Hi @cripplePX and @KelSolaar,

I also encountered with this problem, I've taken a look into the code and some findings as below.

Summary

The core of the issue is that the method parameter in plot_RGB_chromaticities_in_chromaticity_diagram is correctly used to calculate the chromaticity coordinates of the input RGB value, but it is not passed down to the chromaticity_diagram_callable which is responsible for drawing the background diagram. This results in the plotted point having coordinates for the chosen method (e.g., 'CIE 1960 UCS'), while the background diagram remains the default 'CIE 1931'.

Perhaps should use plot_RGB_chromaticities_in_chromaticity_diagram_CIE1931 and plot_RGB_chromaticities_in_chromaticity_diagram_CIE1960UCS instead of using the lower level function.

Code to Demonstrate the Issue

Here is an example that uses a proxy callable to inspect the arguments being passed to the background plotting function.

from colour.plotting.models import (
    plot_RGB_chromaticities_in_chromaticity_diagram,
    plot_RGB_colourspaces_in_chromaticity_diagram,
)


"""
def plot_RGB_chromaticities_in_chromaticity_diagram(
    RGB: ArrayLike,
    colourspace: (
        RGB_Colourspace | str | Sequence[RGB_Colourspace | LiteralRGBColourspace | str]
    ) = "sRGB",
    chromaticity_diagram_callable: Callable = (
        plot_RGB_colourspaces_in_chromaticity_diagram
    ),
    method: (Literal["CIE 1931", "CIE 1960 UCS", "CIE 1976 UCS"] | str) = "CIE 1931",
    scatter_kwargs: dict | None = None,
    **kwargs: Any,
) -> Tuple[Figure, Axes]:
"""

red_rgb = (1.0, 0.0, 0.0)


def debug_chromaticity_diagram_callable(**kwargs):
    print("diagram callable received method:", kwargs.get("method"))
    # This will print "None", causing the default 'CIE 1931' diagram.
    return plot_RGB_colourspaces_in_chromaticity_diagram(**kwargs)


plot_RGB_chromaticities_in_chromaticity_diagram(
    RGB=red_rgb,
    colourspace="sRGB",
    method="CIE 1960 UCS",
    chromaticity_diagram_callable=debug_chromaticity_diagram_callable,
)

# Output: Point in space CIE 1960 UCS, but diagram is CIE 1931 xy.

Bug or Intended Behavior

This leads to the question of whether this is a bug or by design.

a bug:
A user providing the method parameter would reasonably expect it to change the entire plot, including the background diagram. The current behavior is confusing because the point is plotted in one coordinate system while the axes and gamut boundary are from another.

behavior:
As I investigated, I noticed that plot_RGB_chromaticities_in_chromaticity_diagram is not imported into the top-level colour.plotting namespace. This suggests it might be an internal helper function. The primary API might be the specific functions like plot_RGB_chromaticities_in_chromaticity_diagram_CIE1931. In that context, the function is always called with a chromaticity_diagram_callable that is already hard-coded for a specific diagram.

Hope this analysis helps clarify the issue.

[KelSolaar]

Hi @Jackchou00,

Thanks for taking the time to investigate, appreciated! This is the intended behaviour indeed: If the method parameter was also selecting/enforcing the chromaticity_diagram_callable, it would not allow for passing a custom callable that draws the chromaticity diagram differently. The method parameter is mostly driving the coordinates computation/transformation aspect of the plot_RGB_chromaticities_in_chromaticity_diagram definition.

It can certainly catch people off guard but as you pointed out, this is a lower level definition and really intended to be used by ourselves. As we are passing the method value to the callable, we could potentially consider raising an error or issue a warning if mismatching.