Two years ago I found with and article or video on how to do lens cast corrections on RAW files taken with a shift lens. This requires using a calibration image taken through an white plastic sheet at the time the original image is taken. The color casting produced is uneven and was a product of shifting the lens. I was able to do this and it worked great. Unfortunately I have lost the instructions and have been unable to figure out what I did. After 6 hours of searching the net, I can;t find the tutorial. This was not a flat -field correction.