Beat Frequencies and Spatial Resolution: Q: What is a beat frequency? A: A beat frequency occurs when similar frequencies and their harmonics interact. Q: What?????? A: Uhhhh, ok. Try this, hold your two hands straight out and touching at the thumbs, with all fingers outstretched and pointing up, with about 1/2" between the tips of each finger. Now rotate the hand so that the fingers pass over each other. A pattern is perceived because of the intersection of your fingers. This is a beat frequency event. When dealing with digital imaging, one has to contend with the interaction of frequencies. In this specific example, the eye image was scanned from a newspaper photograph made up of fine patterns of small dots. The newspaper image was converted into a digital image by using a flat bed scanner, set to a certain spatial resolution (600 dpi or dots per inch). Your monitor is made up of fine dots, usually a 800 x 600 matrix. At certain image sizes, the dots cancel each other out, or add together to create visual artifacts. The only thing that has changed with the succession of images left to right is the degree to which the image was magnified. Visual artifacts of this nature are possible in medical imaging in cases where a stationary or stalled grid imposes fine lines on the CR cassette, and these "beat" against the image sample frequency. These are all the same image, but because of beat frequency effects, substantial artifacts are generated. Click on the image to see it full size... Click on this link to see a simplified example of the pheonomenon Image 1 Click on this link to see another example Image 2