Masked array

with rasterio.open(self.source.path) as src:
    tile_bounds_src_crs = rasterio.warp.transform_bounds(TILE_CRS, src.crs, *tile_bounds)
    tile_window = src.window(*tile_bounds_src_crs)
    tile_data = src.read(window=tile_window, boundless=True, masked=True)
    tile_transform = src.window_transform(tile_window)

    # translate the values into the desired range
    if self.scaled_min_max_pixel_values:
        for i, scaled_vals in enumerate(self.scaled_min_max_pixel_values):
            try:
                tile_data[i] = numpy.interp(tile_data[i],
                                            [tile_data[i].min(), tile_data[i].max()],
                                            scaled_vals)
            except IndexError:
                logger.warn('Too many scaled_min_max_values passed')

    kwds = {
        'transform': rasterio.transform.from_bounds(*tile_bounds, TILE_SIZE, TILE_SIZE),
        'driver': 'PNG',
        'dtype': 'uint8',
        'height': TILE_SIZE,
        'width': TILE_SIZE,
        'crs': TILE_CRS,
        'count': src.count + 1
    }

    with MemoryFile() as memfile:
        with memfile.open(**kwds) as dst:
            for i in range(1, src.count + 1):
                reproject_args = {
                    'source': tile_data[i-1],
                    'src_crs': src.crs,
                    'src_transform': tile_transform,
                    'destination': rasterio.band(dst, i),
                    'resampling': rasterio.enums.Resampling.average,
                    'dst_alpha': src.count + i
                }

                logger.info(f'reprojecting with kwds {reproject_args}')
                rasterio.warp.reproject(**reproject_args)

        # normal png tiles, read the chunk of memfile as a bytearray
        return memfile.read()