Use IDL language for this image analysis question

For the lit-side image, here is the center in X and Y coordinates, and in longitude and radius: XCEN DOUBLE = 175.69387 ,YCEN DOUBLE = 515.98748 ,RCEN DOUBLE = 134487.62 ,LCEN DOUBLE = 294.17136 .For the unlit-side image, here is the center in X and Y coordinates, and in longitude and radius: XCEN DOUBLE = 276.12855 ,YCEN DOUBLE = 846.10222 ,RCEN DOUBLE = 134413.19, LCEN DOUBLE = 346.36962 What we want to do now is this: Take the radius and longitude values for each pixel in each image, subtract rcen or lcen as appropriate, and then youll have the relative radius and longitude values with the origin at the center of the image. You then want to compare the brightness at a given coordinate on the lit side with the brightness at the same coordinate on the unlit side. In order to do this, use the INTERPOL and INTERPOLATE functions. A given pixel in the unlit-side (that is, for integer X and Y values) has radius and longitude values that you know. Youll want to use INTERPOL to find the X and Y coordinates on the lit side that correspond to the same radius and longitude values. Because these X and Y coordinates will be floating-point decmials and not integers, youll then want to use the INTERPOLATE function to find the pixel value of the lit-side image at that coordinate. write a script to do this job in IDL language.