cvConvertScale error - opencv

Question

I am new to Python and openCV so if this is simple I apologize in advance.
I am trying to follow the depth map code at http://altruisticrobot.tistory.com/219.
In the code below ConvertScale raises the following error:
src.size == dst.size && src.channels() == dst.channels()
I have spent a couple days and cant figure out why.
Any pointers would be greatly appreciated.
Thanks in advance.
im_l = cv.LoadImage('C:\Python27\project\captureL6324.png',cv.CV_LOAD_IMAGE_GRAYSCALE)
im_r = cv.LoadImage('C:\Python27\project\captureR6324.png',cv.CV_LOAD_IMAGE_GRAYSCALE)
imsize = cv.GetSize(im_l)
disp = cv.CreateImage(imsize,cv.IPL_DEPTH_16S,1)# to receive Disparity
#run stereo Correspondence-- returns a single channel 16 bit signed disparity
disparity = cv.FindStereoCorrespondenceBM(im_r,im_l,disp,cv.CreateStereoBMState())
#convert to a real disparity by dividing it by 16-- first create variable to hold the converted scale
real_disparity = cv.CreateImage(imsize,cv.IPL_DEPTH_16S,1)
cv.ConvertScale(disparity, real_disparity, -16,0)
#get the point cloud
depth = cv.CreateImage(cv.GetSize(im_l),cv.IPL_DEPTH_32F,3)
cv.ReprojectIMageTo3D(real_disparity,depth, ReprojectMatrix)

Answer 1

Your problem is, that FindStereoCorrespondenceBM saves the result in the third parameter but you are using the return value, which is None for further computation. This leads to an error since a matrix of a certain size and type is expected.
So just change
cv.ConvertScale(disparity, real_disparity, -16,0)
to
cv.ConvertScale(disp, real_disparity, -16,0)
To run the whole script I also changed the last line to
ReprojectMatrix = cv.CreateMat(4,4,cv.CV_32FC1);
cv.ReprojectImageTo3D(real_disparity,depth, ReprojectMatrix)
This script runs without error for me. But I have not checked whether it gives the correct result.