PNG file has invalid signature

Question

I'm working on panoramic image stitching and in imread function i got format error:PNG file has invalid signature.I googled it but i did not find anything.Can you explain me reason of error?

EDIT: baseInputPath+path=Input/PanoramaImage30/image1.png

baseInputPath='Input/'
baseOutputPath='Output/'

def imread(path='in.png'):
    '''reads a PNG RGB image at baseInputPath+path and return a numpy array organized along Y, X, channel.
    The values are encoded as float and are linearized (i.e. gamma is decoded)'''
    global baseInputPath
    print baseInputPath+path
    reader=png.Reader(baseInputPath+path)
    im=reader.asFloat()
    a=numpy.vstack(im[2])
    if im[3]['greyscale']:
        raise NameError( 'Expected an RGB image, given a greyscale one')        
    x, y=im[0], im[1]
    a.resize(y, x, 3)
    a**=2.2
    return a

Answer 1

在开始时我将jpeg文件转换为png，因此文件已损坏。现在重新转换它并成功处理。