Hi everyone, I'm stuck with a problem of the python wrapper for OpenCv. I have this function that returns 1 if the number of black pixels is greater than treshold

def checkBlackPixels( img, threshold ):
    width     = img.width
    height    = img.height
    nchannels = img.nChannels
    step      = img.widthStep
    dimtot   = width * height
    data = img.imageData
    black = 0

    for i in range( 0, height ):
        for j in range( 0, width ):
            r = data[i*step + j*nchannels + 0]
            g = data[i*step + j*nchannels + 1]
            b = data[i*step + j*nchannels + 2]

     if r == 0 and g == 0 and b == 0:
         black = black + 1

     if black >= threshold * dimtot:
        return 1
     else:
        return 0  

The loop (scan each pixel of a given image) works good when the input is an RGB image...but if the input is a single channel image I get this error:

for j in range( width ):
TypeError: Nested sequences should have 2 or 3 dimensions

The input single channel image (called 'rg' in the next example) is taken from an RGB image called 'src' processed with cvSplit and then cvAbsDiff

cvSplit( src, r, g, b, 'NULL' )
rg = cvCreateImage( cvGetSize(src), src.depth, 1 ) # R - G
cvAbsDiff( r, g, rg )

I've also already noticed that the problem comes from the difference image got from cvSplit...

Anyone can help me? Thank you