NGC 4672, amplified images combined

Original appearance (left), after photographic amplification (centre) and seven images combined (right), all at the same scale
Plates taken in blue light with the UK Schmidt Telescope

Analogue photographic amplification works by enhancing the effective size of near-surface image grains by copying the original plate with a diffuse light source and using a high contrast copy film, as seen in this diagram. However, this process also enhances the grain structure as well, which is very evident at high enlargement (centre image).

The grain noise can be reduced by combining several amplified images together. Since the stars and galaxies are the same on all the images, but the photographic grain varies from image to image, the signal to noise is reduced and the faint structures associate with the galaxy can be better seen.

This is one of a series of galaxy images made with UK Schmidt plates that show faint features of bright galaxies. More information on this galaxy is available here.

David Malin 2006 Jan 27