Reading pngs with variable bit depth (for example: LabView wrote a png from a 12-bit camera).

readpng.py

def readpng(filename, hotpixelremove=False):
    '''
    Reads a png file and returns appropriate count vales, even if a bit depth
    other than 8 or 16 is used. An example this might be needed is having a
    12-bit png recorded from a 12-bit camera using LabViews IMAQ toolset.
    In this case the PIL (python image library) fails to retrieve the
    original count values. 
    '''
    import png  # pypng
    import scipy.misc as sm
    import numpy as np
    meta = png.Reader(filename)
    meta.preamble()
    significant_bits = ord(meta.sbit)
    ret = sm.imread(filename)
    ret >>= 16 - significant_bits
    if hotpixelremove:
        import scipy.ndimage
        ret = scipy.ndimage.morphology.grey_opening(ret, size=(3,3))
    return np.float64(ret)