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ccdcross - cross correlate images with a reference image


ccdcross [parameter=value]


ccdcross finds the optimal offset one (or more) images and a reference image based on the cross-correlation between two images. By selecting a specific center= and half box= size, one can focus on a specific area, assuming the offset is less than the box-size.


The following parameters are recognized in order; they may be given in any order if the keyword is also given. Use --help to confirm this man page is up to date.
Input image files, first image is the reference image. At least two images need to be given. No default.
Output cross image. No default.
X-Y Reference center around which a box (see box= below) is taken. The are 0-based integer pixels. By default the center of the image is used. Default: center of first input image.
Half size of correlation box. The output image is forced to have an odd pixel size, 2*box+1. The shift between the images should not exceed box. By default half the mapsize is used.
Only use values above this clip level. By default values are not clipped.
bad value to ignore. By default there is no bad value recognized.


Only 2D images are handled.

The WCS is ignored, 0-based pixel coordinates are reported.

Images should ideally be the same size, but nothing will stop the program from running off without that. The user is then responsible for computing the true offsets as all bets are off.


Here two gaussian shaped sources with noise are created with a small 1 pixel offset from each other.

ccdgen - gauss 1,2 size=128,128 center=64,64 | ccdgen g64 noise spar=0,0.05 in=-
ccdgen - gauss 1,2 size=128,128 center=65,65 | ccdgen g65 noise spar=0,0.05 in=-
ccdcross g64,g65 shift.ccd box=16
### nemo Debug Info: Max cross 13.968 @ 16 16
### nemo Debug Info: X,Y mean: 0.393391 0.412221
### nemo Debug Info: X,Y sig: 1.7885 1.76623
### nemo Debug Info: Center at: 0.393391 0.412221
0.393391 0.412221 0.393391 0.412221 16 16 13.968

See Also

ccdmath(1NEMO) , image(5NEMO)


src/image/mics    ccdcross.c


Peter Teuben

Update History

11-Apr-2022    V0.1 Created    PJT
3-aug-2023    V0.2 fix absolute coordinate    PJT
18-apr-2024    V0.3 add peak flux in correlation map    PJT

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