If I expose, as in the next image, to capture as much as possible of the tail, no hint of the bright nucleus appears in the overexposed head. Yet, when you observe the comet visually, you have no difficulty seeing all the detail at once. The reason is that unlike the linear response of photographic film to light, the eye's response is approximately logarithmic, which allows you to simultaneously perceive a much wider dynamic range of intensity. Electronic imaging allows approximating human perception much more closely. This means that a CCD image may contain more information than a cursory glance reveals.
Image processing can tease out latent images impossible to capture on conventional film.
If the response of the human eye is logarithmic, then suppose we simply replace each pixel in the image with a pixel whose intensity is the logarithm of the original pixel. In fact, this results in an image strikingly similar to the appearance of the comet's head to the human eye. Having the image in digital form makes it easy to prepare false colour renderings in which different intensities are represented by colour. The eye is far more sensitive to changes in colour than slow gradations of intensity, so such renderings may reveal detail difficult to notice in a grey scale image. In each of the images below the scale at the bottom shows the colour palette assigned to intensities with the minimum at left and the maximum at right.