I had a delightful conversation with Doug Yoon the founder of XDR Radiology. Dr. Yoon is both a dentist and a mathematician who has worked at UCLA and elsewhere on image processing and computer aided diagnosis.
We discussed a number of myths regarding digital radiography. This one was a big surprise to me.
When you underexpose a digital radiograph it does not usually show up as a light washed out image. That is what we see with film and it is what we expect with digital. What happens instead is that in most cases the software automatically adjusts the image brightness in such a way that it looks like a good exposure. However the fact is that an underexposed image has much less data than a properly exposed image and is much less diagnostic. Instead of appearing washed out an underexposed digital image will appear grainy or blurred.
In fact Dr. Yoon believes that a common reason for poor quality digital radiographs is not the sensor, not the computer, not the monitor but is underexposure. Dental offices often underexpose the sensor which reduces the diagnostic quality of the image but because the image does not look light and washed out they think it is a proper exposure.