On a side note, can't we get a real bug tracker somewhere? --- I have a selection of grayscale (8bit) tifs in a directory. In [14]: k = io.ImageCollection("calib/*.tif", True) In [15]: k[0].dtype Out[15]: dtype('uint8') In [16]: k = io.ImageCollection("calib/*.tif", as_grey=True) In [17]: k[0].dtype Out[17]: dtype('float32') --- But the docs say: as_grey : bool, optional If True, convert the input images to grey-scale. This does not affect images that are already in a grey-scale format. Obviously the image data type gets converted though. Cheers, Holger