Disparity with 32FC1?

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Hello,

I'm obtaining the disparity map (using a ros node) and I get that the encoding is 32FC1. How do I obtain the disparity for each pixel to obtain the depth in Z?

According to the formulas, I should do Z = f.b / d. f being the focal length, b the baseline and d the disparity. But for d in a pixel coordinate (u, v) from the rectified images I get four values (RGBA I guess). How do I get the real value for d from this four values?

Thanks for the help.