ringavg: Compute pixel averages in concentric rings about given center

Package: proto

Usage

ringavg image xc yc

Parameters

image

Image to be used.

xc, yc

Pixel coordinate for center of rings.

r1 = 0, r2 = 10, dr = 1

Rings to be measured. r1 is the inner radius of the first ring, r2 is the outer radius of the last bin, and dr is the widths of the rings. The values are in units of pixels.

labels = yes

Print column labels for the output?

vebar = no

If vebar is yes then the standard deviation and standard error will be printed as negative values for use with graph.

Description

Pixels are binned into a series of concentric rings centered on a given position in the input image. The rings are defined by an inner radius for the first ring, an outer radius for the last ring, and the width of the rings. The statistics of the pixel values in each ring are then computed and list to the standard output. The output lines consist of the inner and outer ring radii, the number of pixels, the average value, the standard deviation of the value (corrected for population size), and the standard error. The parameter label selects whether to include column labels.

If the ring average are to be plotted with the task graph using the option to plot error bars based on the standard deviation or standard error then the vebar parameter may be set to write the values as negative values are required by that task.

This task is a script and so users may copy it and modify it as desired. Because it is a script it will be very slow if r2 becomes large.

Examples

1. Compute the ring averages with labels and output to the terminal.

cl> ringavg pwimage 17 17
#  R min    R max     Npix    Average    Std Dev    Std Err
    0.00     1.00        5      7.336       9.16      4.096
    1.00     2.00        8     0.2416     0.2219    0.07844
    2.00     3.00       16     0.3994     0.5327     0.1332
    3.00     4.00       20    0.06211    0.05491    0.01228
    4.00     5.00       32     0.0987    0.08469    0.01497
    5.00     6.00       32    0.06983    0.06125    0.01083
    6.00     7.00       36     0.0641     0.0839    0.01398
    7.00     8.00       48    0.06731    0.05373   0.007755
    8.00     9.00       56    0.06146    0.07601    0.01016
    9.00    10.00       64    0.05626    0.05846   0.007308

2. Plot the ring averages with standard errors used for error bars.

cl> ringavg pwimage 17 17 label- vebar+ | fields STDIN 2,4,6 |
>>> graph point+ marker=vebar

3. Plot ring averages for galaxy in dev$pix.

cl> ringavg dev$pix 256 256 r2=100 dr=5 label- | fields STDIN 2,4 |
>>> graph logy+

See also

pradprof, psfmeasure, radprof