detect_sources

photutils.segmentation.detect_sources(data, threshold, npixels, filter_kernel=None, connectivity=8, mask=None)[source]

Detect sources above a specified threshold value in an image and return a SegmentationImage object.

Detected sources must have npixels connected pixels that are each greater than the threshold value. If the filtering option is used, then the threshold is applied to the filtered image. The input mask can be used to mask pixels in the input data. Masked pixels will not be included in any source.

This function does not deblend overlapping sources. First use this function to detect sources followed by deblend_sources() to deblend sources.

Parameters
dataarray_like

The 2D array of the image.

thresholdfloat or array-like

The data value or pixel-wise data values to be used for the detection threshold. A 2D threshold must have the same shape as data. See detect_threshold for one way to create a threshold image.

npixelsint

The number of connected pixels, each greater than threshold, that an object must have to be detected. npixels must be a positive integer.

filter_kernelarray-like (2D) or Kernel2D, optional

The 2D array of the kernel used to filter the image before thresholding. Filtering the image will smooth the noise and maximize detectability of objects with a shape similar to the kernel.

connectivity{4, 8}, optional

The type of pixel connectivity used in determining how pixels are grouped into a detected source. The options are 4 or 8 (default). 4-connected pixels touch along their edges. 8-connected pixels touch along their edges or corners. For reference, SourceExtractor uses 8-connected pixels.

maskarray_like of bool, optional

A boolean mask, with the same shape as the input data, where True values indicate masked pixels. Masked pixels will not be included in any source.

Returns
segment_imageSegmentationImage or None

A 2D segmentation image, with the same shape as data, where sources are marked by different positive integer values. A value of zero is reserved for the background. If no sources are found then None is returned.

Examples

# make a table of Gaussian sources
from astropy.table import Table
table = Table()
table['amplitude'] = [50, 70, 150, 210]
table['x_mean'] = [160, 25, 150, 90]
table['y_mean'] = [70, 40, 25, 60]
table['x_stddev'] = [15.2, 5.1, 3., 8.1]
table['y_stddev'] = [2.6, 2.5, 3., 4.7]
table['theta'] = np.array([145., 20., 0., 60.]) * np.pi / 180.

# make an image of the sources with Gaussian noise
from photutils.datasets import make_gaussian_sources_image
from photutils.datasets import make_noise_image
shape = (100, 200)
sources = make_gaussian_sources_image(shape, table)
noise = make_noise_image(shape, distribution='gaussian', mean=0.,
                         stddev=5., seed=0)
image = sources + noise

# detect the sources
from photutils.segmentation import detect_threshold, detect_sources
threshold = detect_threshold(image, nsigma=3)
from astropy.convolution import Gaussian2DKernel
kernel_sigma = 3.0 / (2.0 * np.sqrt(2.0 * np.log(2.0)))  # FWHM = 3
kernel = Gaussian2DKernel(kernel_sigma, x_size=3, y_size=3)
kernel.normalize()
segm = detect_sources(image, threshold, npixels=5,
                      filter_kernel=kernel)

# plot the image and the segmentation image
import matplotlib.pyplot as plt
fig, (ax1, ax2) = plt.subplots(2, 1, figsize=(8, 8))
ax1.imshow(image, origin='lower', interpolation='nearest')
ax2.imshow(segm.data, origin='lower', interpolation='nearest')

(Source code, png, hires.png, pdf, svg)

../_images/photutils-segmentation-detect_sources-1.png