import rasterio
src = rasterio.open('../image.tif', mode='r')
data_mask = src.read_masks(1)
data = src.read(1)

array([[255, 255, 255, ..., 254, 255, 255],
       [255, 255, 255, ..., 254, 255, 255],
       [255, 255, 255, ..., 254, 255, 255],
       ...,
       [255, 255, 255, ..., 248, 252, 248],
       [254, 254, 254, ..., 255, 235, 253],
       [255, 255, 255, ..., 255, 255, 245]], dtype=uint8)

array([[255, 255, 255, ..., 255, 255, 255],
       [255, 255, 255, ..., 255, 255, 255],
       [255, 255, 255, ..., 255, 255, 255],
       ...,
       [255, 255, 255, ..., 255, 255, 255],
       [255, 255, 255, ..., 255, 255, 255],
       [255, 255, 255, ..., 255, 255, 255]], dtype=uint8)

gdal_translate -b mask -of vrt -a_nodata 0 test.tif test.vrt
gdal_translate -b 1 -of vrt -a_nodata 0 test.vrt test2.vrt
gdal_polygonize.py -q  -8 test2.vrt -b 1 -f "ESRI Shapefile" testdata.shp

gdalwarp -dstnodata 0 -dstalpha -of GTiff foo1 foo2
gdal_polygonize.py foo2 -b 2 -f "ESRI Shapefile" foo3