An improvement of an optical method for in situ measurement of the intrinsic stress in thin films is described. The method presented is based on the well-known beam bending technique using the deflection of a laser beam that reflects itself on a sample. The first new development lies in the evaluation of the bending plate equation. The second uses image processing to determine the deformation of the sample. The method has been applied to pure chromium films on glass substrates to validate the stress measurements. The reproducibility of stress measurement is of about 8%. Results show the great adaptability of the technique to any kind of stress evolution during the physical vapor deposition process and give additional information about the evolution of stress versus film thickness, in comparison with ex situ techniques, Finally, a correlation between stress measurement and microstructure has been carried out.