Function: Excise Central 2^n x 2^n Region

	Function: Excise Central 2^n x 2^n Region
Function	This function will excise the largest possible central square (power of 2) region of a passed in image.
Version	version:201503015, v1.0
Author	D. R. G. Mitchell
Acknowledgements	-
Comments	This function will excise the largest possible square region from the centre of a passed in image. The excised image has a power of 2 side length which makes it suitable for FFT-based processing. This can be useful for many things including cross-correlation-based image alignment.
System Requirements	Should be compatible with all recent versions of DigitalMicrograph.
Known Issues	-
Supported	Yes
Included Files	Main script file.
Source Code	// Function which excises the central 2^n x 2^n portion of an image (where n is an integer). // This can be a useful prelude to cross-correlation, for such things as image alignment. // version:150315, v1.0 // D. R. G. Mitchell, adminnospam@dmscripting.com (remove the no spam to make this address work) // March 2015, www.dmscripting.com // Function to excise the largest possible square region from the passed in image. The excised region will be centred within // the image and will have side length which is an integer power of 2. image ExciseCentral2nby2n(image source) { // Get some info on the passed in image number xsize, ysize getsize(source, xsize, ysize) // Work out the maximum 2^n ROI number xmod=log2(xsize) xmod=xmod-mod(xmod,1) number ymod=log2(ysize) ymod=ymod-mod(ymod,1) xmod=2xmod ymod=2ymod number xcentre=xsize/2 number ycentre=ysize/2 number top, left, bottom, right // Work out the ROI and excise it top=ycentre-(ymod/2) left=xcentre-(xmod/2) bottom=ycentre+(ymod/2) right=xcentre+(xmod/2) image excised=source[top, left, bottom, right] return excised } // Main Program - ensure an image is displayed to test this function image front:=getfrontimage() image excise=excisecentral2nby2n(front) showimage(excise)

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