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Name

ccdblob - properties of a blob in an image

Synopsis

ccdblob [parameter=value]

Description

ccdblob is a poor man’s source extractor and computes some properties of a blob ("star") in an image. With given rough pixel coordinates and a box size, it will determine the peak, shape and flux of the blob, assuming the background signal (box needs to be big enough for this) is well characterised by the median value. This current algorithm thus does not work in crowded fields.

The current draft version is based off ccdshape(1NEMO) and thus inherits some keywords and output that may disappear or change meaning.

Pixel coordinates are 1-based.

Parameters

The following parameters are recognized in any order if the keyword is also given:
in=
Input NEMO image file
No default.
pos=
(x,y) center of the box, or use maximum in image (?). Positions are 1-based integers.
Default is center of image, but there should be an option to use the maximum in the image?
box=
Box size to use around pos.
Default: 32
clip=
Use only values above clip.
Default will use all values
wcs=t|f
Use WCS of the cube (otherwise use pixel coordinates 1..N).
radecvel=t|f
Split the RA/DEC from VEL
[f]
weight=t|f
Weigh moments of inertia by intensity?
[t]
cross=
Use cross correlations between X and Y to...
peak=N
Find the N-th peak. Only used if pos is not given. For peak=0 the center of the map is used, otherwise it will find the N-th peak.
Default: 1

not implemented yet

Examples

Analysing a Betelgeuse images from an all-sky camera:

% file=ASC/MASN-01/archive/201601/20160102/IMG00700.FIT % fitsccd $file - | ccdblob - 724,305 BLOB 726 305 724.573 305.38 32 6546 42731 139121

Where the BLOB line lists the peak position (pixels are 1-based), followed by an intensity weighted position, the box size around the estimated center, followed by the median, peak and total blob flux (corrected for the median background).

An example of creation a gaussian blob with a given Signal/Noise (ns=) and running it through ccdblob:

sn=10 ccdgen - gauss 1,3 128,128 | ccdgen - noise 0,1/$sn in=- | ccdblob - Npoints: 1024 DataMinMax: -0.359968 1.08932 Min at: 53 71 (1 based) Max at: 64 65 Mean: 0.0559946 Median: 0.0673992 DataSum: 57.3385 Flux: -11.6783 ImSize: 128 128 1 Center: 63.1595 63.5957 0 [wcs] BLOB: 64 65 64.1595 64.5957 32 0.0673992 1.08932 -11.6783 e_x: 1.00000 0.99981 0.01968 0.00000 90.0 1.1
e_y: 1.00000 -0.01968 0.99981 0.00000 90.0 91.1
e_z: 1.00000 0.00000 0.00000 1.00000 0.0 0.0
qpole: 13.07941 0.99981 0.01968 0.00000
5.93258 -0.01968 0.99981 0.00000
0.00000 0.00000 0.00000 1.00000
a,b: 3.61655 2.43569 inc: 47.6634 (meaningless without radecvel) pa: 91.1275 (meaningless without radecvel)

See Also

ccdstat(1NEMO) , image(5NEMO) 
https://github.com/perwin/imfit

Files

src/image/misc/ccdblob.c

Author

Peter Teuben

History


15-feb-2020    V0.1 Created    PJT
14-feb-2025    V0.3 fix boxsize when no pos given    PJT

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