A popup window will open which offers some basic image processing
options (see Fig. 5.16).
The Image Processing popup window
- Boxcar Smooth
- will apply a boxcar averaging to the
image or spectrum, i.e. each pixel is replaced by the average
of its neighborhood. The width is specified in scan
pixels (which are different from the displayed pixels if you
are on a zoom stage different from 1.0 and if the True Aspect
Ratio box is checked). Check the IDL help on SMOOTH
for more information.
- Median Smooth
- will replace each pixel by the Median of
its neighborhood. Again, the width is specified in Scan
Pixels. Check the IDL help on MEDIAN for more
- Gaussian Smooth
- will replace each pixel by a
Gaussian-weighted average of its neighborhood. The width (1/e
with of the Gaussian) is specified in scan pixels.
Gaussian Smooth is usually preferred over Boxcar smooth,
because its gives greater weight to closer neighbors.
Mathematically, a Gaussian smooth corresponds to a Gaussian
filter in Fourier space, whereas a Boxcar smooth corresponds
to a Sinc filter in Fourier space (which has unwanted side
- Unsharp Masking (Sharpening)
- (not for spectra) will
apply an Unsharp Mask filter to the image. Check the IDL help
on UNSHARP_MASK for more information. The parameters
are currently hard coded to the IDL defaults.
- (not for spectra) will despike the image. Ask
Chris for details about the algorithm.
- Noise Filtering
- (not for spectra) is meant for filtering
out periodic frequencies. It may be useful for getting rid of non-random
line noise for example.
First choose, if you want to have a 1D power spectrum displayed, which
shows the frequencies present in all scan lines added up incoherently,
or the 2D fourier transform of your image. You can then drag the mouse
over the frequency area to be filtered out and choose which type of filter
to use. You can either Smooth out a spike (1D only), Kill it, or apply a
second order Butterworth (BW) or a Gaussian filter of chosen width.
In the 2D case, you can have the fourier transform overlayed with the corresponding
time frequencies (calculated over the pixel dwell), by hitting Show
Frequency. Don't forget to Apply Filter.
- (not for spectra) lets you crop the image. The
button is only sensitive if you have marked a rectangle on
- Undo / Redo
- lets you undo and redo image processing
steps. The number of steps is unlimited (programmatically), so
if you overdo it, you might run out of memory at some point.
These buttons un/redo only image processing, and nothing else!
- Original Image
- lets you undo all image processing
steps and recover the original image. This can't be undone!
- deserves no further explanation.
Some general remarks about image processing:
More image processing tools, like Fourier Filtering or Wiener
Filtering, might be included in the future if users are