Image Degradation on Reprinting Faded Dye-Images

Abstract

The problem of maintaining the quality of fading dye-images by successive reprintings is analysed in terms of the signal-to-noise ratio, (SIN). The analysis takes account of the loss of contrast of fine detail due to light scatter on reprinting and also the build-up of noise due to both granularity and dust, etc. Two special cases are discussed in some detail. It is shown that for the dust-free case, (S/N) depends only on the number of reprintings and not on time, whereas for the second case, the presence of dust introduced at each reprinting can lead to an exponential fall in (SIN) which proceeds at the same rate as the fading itself and is independent of the number of reprintings. In this case, there should be less preferential loss of fine detail. The general conclusions are that information degraded through fading cannot be recovered in practice by successive reprintings but that the fewer reprintings, the better.