A common way of correcting digital images is to use masking layers. How this is done is not important here, but it is worth noting what the resulting effects are should the masking work be done incorrectly. Masks should blend smoothly with the unmasked areas, but if this is not the case then a high tide mark appears around the areas that had previously been masked.
FIGURE 1 In the example on the left, the high tide mark runs around the border between the light and dark areas (indicated), where the light area had originally been masked. In the righthand example the light areas that had been masked incorrectly have become separated from the background, outlined by the same dark line.
Fringing is when opposing colours, usually either Magenta & Green or Blue & Yellow, appear on opposite sides of detail in an image. It is caused by light diffracting when passing through lenses in cameras or scanners, and is more likely to appear towards the corners and sides of an image.
FIGURE 2 Fringing is often seen in files, although not usually as severe as the exaggerated example on the left, but if it is not noticeable when viewed at 100% then there is no need to worry about it.
Noise is the random signals that scanners can generate throughout an image, although this is normally only noticeable in the deep shadows where the light is weakest. It appears as multi-coloured speckling where you would expect to see even tones. Elsewhere in the image the light exposure far outweighs the noise signal, thus hiding it. The problem is most common in under exposed colour negatives as the tonal range is larger than transparencies, which have denser shadow detail. As with fringing, if you can not see the effect viewed at 100% then there is no need to worry.