matplotlib/matplotlib · error · ValueError

"blend_mode" must be callable or one of {lookup.keys}

Error message

"blend_mode" must be callable or one of {lookup.keys}

What it means

Error ""blend_mode" must be callable or one of {lookup.keys}" thrown in matplotlib/matplotlib.

Source

Thrown at lib/matplotlib/colors.py:4108

            An (m, n, 3) array of floats ranging between 0-1.
        """
        # Calculate the "hillshade" intensity.
        intensity = self.hillshade(elevation, vert_exag, dx, dy, fraction)
        intensity = intensity[..., np.newaxis]

        # Blend the hillshade and rgb data using the specified mode
        lookup = {
                'hsv': self.blend_hsv,
                'soft': self.blend_soft_light,
                'overlay': self.blend_overlay,
                }
        if blend_mode in lookup:
            blend = lookup[blend_mode](rgb, intensity, **kwargs)
        else:
            try:
                blend = blend_mode(rgb, intensity, **kwargs)
            except TypeError as err:
                raise ValueError('"blend_mode" must be callable or one of '
                                 f'{lookup.keys}') from err

        # Only apply result where hillshade intensity isn't masked
        if np.ma.is_masked(intensity):
            mask = intensity.mask[..., 0]
            for i in range(3):
                blend[..., i][mask] = rgb[..., i][mask]

        return blend

    def blend_hsv(self, rgb, intensity, hsv_max_sat=None, hsv_max_val=None,
                  hsv_min_val=None, hsv_min_sat=None):
        """
        Take the input data array, convert to HSV values in the given colormap,
        then adjust those color values to give the impression of a shaded
        relief map with a specified light source.  RGBA values are returned,
        which can then be used to plot the shaded image with imshow.

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/colors.py:4108 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of matplotlib/matplotlib@b379c1b69e (2026-08-21). Data as JSON: /api/errors/4826e36f02e6caaf. Report an issue: GitHub.