This paper presents modification method to calculate the depth and cross section area of defects in internal structure of castings by X-Ray radiography technique. Aluminum block incorporate simulated defects which represented by three steel spheres of different sizes and depths, were prepared. Typical radiographs were taken at optimum conditions from two opposite sides of the aluminum alloy block. Then typical radiographs were taken from top side of the aluminum alloy block accomplished by moving the x-ray source at measured interval distances for depth determination. Image J program were used to analysis of the X-Ray films, getting information about the cross section area of the shadow of defects on radiographs and required distance measurement on radiograph, whatever their shape, regular or irregular. Equations derived earlier were adapted to calculate the depth of defects in term of their shadows on radiograph. By compensation the optimum data which got from the Image J program in these equations, the ultimate goal in high accuracy detection of the depth of defects were achieved. The effect of the x-ray fluorescence on the quality of the x-ray image due to use of unsuitable x-ray voltage was also studied. This was achieved by using of different kV to radiograph a test object of (0.1) mm in thickness of Cu and Ag samples.