esp. 

where description says

"This RGB image contains a number of rather bright rings, with pixel values over 1000, on a gray background. The image is useful for testing how filtering and resampling algorithms react to high- dynamic-range data. (Some filters, for example, convolution kernels with negative lobes, tend to produce objectionable artifacts near high-contrast edges.) Note that the rings in the image are smooth, although on most displays clamping of the pixel values introduces aliasing artifacts. To see that the rings really are smooth, view the image with and exposure of -10."