## HDF version 2 noise properties

The attached figures compare the rms fluctuations of the sky background
measured in blank regions of the final drizzled images from version 1
and version 2 of the HDF data reduction. The images have been
successively binned 2x2, 3x3, up to 16x16 pixels to highlight
the fact that the images are * smoother * on pixel scales than
would be computed from a naive application of the CCD noise model.
This is because the image combination process produces correlations
between neighboring pixels.
The figures show the rms fluctuations divided by sqrt(N) where N
is 2 for 2x2 binning, 3 for 3x3 binning, etc. If the noise were
uncorrelated there would be no change in the rms with N.

The open circles show version 1 of the data, with the dashed line
showing the best estimate of the mean for N>6. The filled circles
show version 2 of the data, with the solid line corresponding to
the best estimate of the mean for N>6.

## F300W

## F450W

## F606W

## F814W

Copyright © 1997 The Association of Universities for
Research in Astronomy, Inc. All Rights Reserved.

Harry Ferguson ferguson@stsci.edu 3/01/96