Modified recolor function with a better color distance

whole_palette.py

class EntirePalette:
    # ... omitted

    def recolor(self, image):
        image_shape = image.shape
        image = self._preprocess(image)
        image_colors = np.unique(image, axis=0)

        self_da = da.from_array(
            self.source_pixels.astype(np.long), chunks=(self.chunk_size, 3)
        )
        other_da = da.from_array(
            image_colors.reshape(-1, 1, 3).astype(np.long),
            chunks=(self.chunk_size, 1, 3)
        )

        # Perceptually "better" color distance.
        rmean_da = (other_da[:, :, 0] + self_da[:, 0]) // 2
        rgb_da = other_da - self_da
        r_da = ((512 + rmean_da) * rgb_da[:, :, 0] ** 2) >> 8
        g_da = 4 * rgb_da[:, :, 1] ** 2
        b_da = ((767 - rmean_da) * rgb_da[:, :, 2] ** 2) >> 8
        result_da = (r_da + g_da + b_da).argmin(axis=1)

        with ProgressBar():
            mapping_idx = idxs_da.compute()

        colormap = {tuple(a): tuple(b)
                    for a, b in
                    zip(image_colors, self.source_colors[mapping_idx])}

        image_recolored = np.array([colormap[tuple(rgb)] for rgb in image])
        return image_recolored.reshape(image_shape).astype(np.uint8)