Source Properties Table

The CImExtract:Extract method creates a table of source properties for the sources it detects and characterizes in an image. For each source, the CImExtract:GetSource method returns a table of source properties as described below.

The returned table can be either a numerically indexed table (array) or a keyed table using the property names. For example, if the table returned by GetSource is named obj, then the center X coordinate is given by either obj.nCenterX or obj[11]. The return type for the Source Properties table (indexed table or keyed table) is controlled by the bUseIndex flag in the call to GetSource. If bUseIndex is omitted or false, a keyed table is returned containing named properties. If bUseIndex=true, then an indexed table is returned. In the table below, the property index is listed under the heading Index. The property name is listed under the heading Name.

Note that some values naturally involve an integer type value, such as iIndex or iMinY. Values beginning with the letter "i" may be processed by your script as either a number or integer value.

Index	Name	Description
1	nDetectThreshold	The threshold number of sigmas above true background used for detecting the source.
2	nBackground	The threshold luminosity value used for detecting the source, a number for the .
3	nBackgroundLocal	The local background value near the source, calculated using dThreshold sigmas above the local true background.
4	nArea	The source area, in pixels.
5	nTotalLum	The total luminosity of the source relative to a pixel value of zero.
6	nNetLum	The net luminosity of the source above the background value, nBackground.
7	nAvgLum	The average luminosity of the source above the background value, nBackground.
8	nLumStdDev	The standard deviation in luminosity above the background value, nBackground.
9	nMinVal	The minimum pixel value in the source.
10	nMaxVal	The maximum pixel value in the source.
11	nCenterX	The luminosity weighted x-coordinate of the source.
12	nCenterY	The luminosity weighted y-coordinate of the source.
13	nCenterWorldX	The luminosity weighted world x-coordinate of the source.
14	nCenterWorldY	The luminosity weighted world y-coordinate of the source.
15	nMag	The astronomical magnitude of the source.
16	nMagErr	The empirical (measured) uncertainty in the astronomical magnitude of the source.
17	nMagErrT	The theoretical (calculated) uncertainty in the astronomical magnitude of the source.
18	nNetCount	The net count of the source above background.
19	nSNR	The signal to noise ratio of the source.
20	nRadiusGyration	The radius of gyration of the source.
21	nMajorAxis	The major axis length, a, of the source.
22	nMinorAxis	The minor axis length, b, of the source.
23	nEllipticity	The ellipticity of the source, in terms of 1-b/a.
24	nAngle	The angle of the major axis of the source, relative to the positive x-axis.
25	nPeakiness	The peakiness index of the source.
26	nConcentrationIndex	The concentration index of the source.
27	nEffectiveDiameter	The weighted diameter of the source.
28	nSkewnessX	The source skewness as a statistical measure of profile symmetry in the x-coordinate direction.
29	nSkewnessY	The source skewness as a statistical measure of profile symmetry in the y-coordinate direction.
30	nKurtosis	The source kurtosis as a statistical measure of flatness.
31	nFwhm	The FWHM of the source from the profile fit.
32	nFwhmPeak	The FWHM peak value from the profile fit.
33	nFwhmBg	The background level of the source from the profile fit.
34	iIndex	The numeric index of the detected source. Holes appear in the original sequence of indices when sources are merged and the secondary source is eliminated as a separate entity. This is an integer value.
35	iMinX	The minimum x-coordinate (column number) of the source above background. This is an integer value.
36	iMaxX	The maximum x-coordinate (column number) of the source above background. This is an integer value.
37	iMinY	The minimum y-coordinate (row number) of the source above background. This is an integer value.
38	iMaxY	The maximum y-coordinate (row number) of the source above background. This is an integer value.
39	iXatMinY	The x-coordinate (column number) at the minimum y-coordinate (row number) of the source above background. This is an integer value.
40	iXatMaxY	The x-coordinate (column number) at the maximum y-coordinate (row number) of the source above background. This is an integer value.
41	iYatMinX	The y-coordinate (row number) at the minimum x-coordinate (column number) of the source above background. This is an integer value.
42	iYatMaxX	The y-coordinate (row number) at the maximum x-coordinate (column number) of the source above background. This is an integer value.
43	iXatMinLum	The x-coordinate (column number) at the minimum luminosity of the source above background. This is an integer value.
44	iXatMaxLum	The x-coordinate (column number) at the maximum luminosity of the source above background. This is an integer value.
45	iYatMinLum	The y-coordinate (row number) at the minimum luminosity of the source above background. This is an integer value.
46	iYatMaxLum	The y-coordinate (row number) at the maximum luminosity of the source above background. This is an integer value.
47	iFirstX	The first x-coordinate (lowest column number) at the start of the source. This is an integer value.
48	iFirstY	The first y-coordinate (lowest row number) at the start of the source. This is an integer value.
49	nDetectThreshold2	Currently unused.

Example

Suppose an image window exists on the Mira screen. The script below performs source extraction on an image from this window and then repeatedly uses GetSource to fetch the (x,y) coordinates from each source's Source Properties table.

Before calling Extract, the default configuration is updated using a ImExtractParams table. Note that your ImExtractParams table does not need to be named Params as shown here.

V = attachlist_imageview()	-- attach an image window
Assert( V, "No image window")	-- leave script if no image window

I = V:GetImage()	-- get the top-most or only image
Assert( I, "No image selected")	-- leave script if no image

E = new_imextract()	-- create a CImExtract object
Params =	-- setup an ImExtractParams table
{	-- use a comma after each "name=value" pair
bProcFilter = true,
bFilterUseSepMin = true,
nFilterSepMin = 10,
bFilterUseAreaMax = true,
nFilterAreaMax= 100,
nBgMethod = 1,
nDetectTreshold = 45,	-- threshold value = 45
nDetectTest = 0,	-- detect pixels >= threshold
}
E:SetParams(Params)	-- set new configuration properties

bOK = E:Extract( I )	-- extract sources from image I
if not bOK then Exit("Extract failed.\n") end

-- report the number of sources extracted:
nCount = E:Count()
if nCount < 1 then Exit("No sources.\n") end
Printf("Number of sources = %d\n", nCount)

-- list the x,y coordinates for all sources:
for i = 1,nCount do
local Stbl = E:GetSource(i)	-- fetch the properties of source i
Printf("[%d]:%lg,%lg\n", i,Stbl.nCenterX,Stbl.nCenterY)
end

Example

Related Topics