Posts tagged visualization

flicker_image

Visualizing noisy images

May 13th

Posted by Anthony in Computing

No comments

You have an image. Each pixel has a value with some uncertainty. How do you visualize the uncertainty in each pixel? Like this:

flicker_image

Here's the Python code

import numpy as np
from matplotlib import pyplot as plt
 
class FlickerImage(object):
    def __init__(self, im, err):
        self.im = im.copy()
        self.err = err.copy()
        finite = np.isfinite(self.im + self.err)
        self.vmin = (self.im - 2 * self.err)[finite].min()
        self.vmax = (self.im + 2 * self.err)[finite].max()
        self.im[np.invert(finite)] = self.vmax
        self.err[np.invert(finite)] = 0
    def flicker(self):
        fg = plt.imshow(np.zeros(self.im.shape),
                        interpolation='nearest',
                        vmin=self.vmin,
                        vmax=self.vmax)
        while True:
            ran = np.random.normal(size=im.shape)
            fg.set_data(im + err * ran)
            plt.draw()

And here's an example script:

import pyfits
f = pyfits.open('file.fits')
im = f["IMAGE"].data
err = f["ERROR"].data
flicker_image = FlickerImage(im, err)
flicker_image.flicker()
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Python, FITS and DS9

Apr 1st

Posted by Anthony in Computing

No comments

Here's an easy way to display FITS images (or any array) in DS9 using Python (with PyFITS, NumPy and Numdisplay, which is part of stsci_python). First launch DS9, then in Python:

import numdisplay
import pyfits
arr = pyfits.getdata('file.fits')
numdisplay.display(arr)

Easy!

Alternatively, the Kapteyn package seems excellent, and uses Python's matplotlib for displaying images. It requires WCSLIB to run, though, so the installation process is a bit longer [update: apparently that bit is no longer true - 17 Oct 2011].

A third option is to use python-sao:

import pysao
import pyfits
ds9 = pysao.ds9()
f = pyfits.open('file.fits')
ds9.view(f[0])

Easy again! And the WCS information is preserved, which doesn't seem to be the case with Numdisplay.

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