Cross Correlation of Two Images
Cross Correlation of Two Images
This option calculates the cross correlation function for two images. Each
of the images is divided into rectangular blocks. Each block in the first
image is correlated with its corresponding block in the second image to
produce the cross correlation as a function of position.
The cross correlation may be used to determine the degree of similarity
between two similar images, or, with the addition of a linear offset to one
of the images, the spatial shift or spatial correlation between the images.
Buffer containing first source image ?
Two source images must be specified. Any DigImage buffer may be used,
except buffer zero.
Buffer containing second source image ?
This entry specifies the second source image. Again, any DigImage buffer
may be used except buffer zero.
Place correlation in which buffer ?
The evaluated correlation function will be placed in the buffer specified
by this entry. Any DigImage buffer may be used. The selected buffer will be
made the current output buffer. The correlation data will be overlayed on
the existing contents of the selected buffer.
Height of correlation cell ?
Each of the source images is divided into rectangular cells between which
the correlation is made. This entry determines the height (in pixels) of
the cells. The cells are always an odd number of pixels in height. If an
even number is specified, then the next odd number will be used. Note that
neighbouring cells may overlap.
Width of correlation cell ?
This entry determines the width (in pixels) of the cells used to evaluate
the correlation functions. The cells are always an odd number of pixels in
width. If an even number is specified, then the next odd number will be
used. Note that neighbouring cells may overlap.
Vertical spacing between evaluations ?
The correlation function need not be evaluated for every pixel in the
image. Frequently sufficient information may be gathered by evaluating it
with non-overlapping correlation cells. This entry specifies the vertical
spacing (in pixels) between correlation function evaluations.
Horizontal spacing between evaluations ?
This entry specifies the horizontal spacing (in pixels) between correlation
function evaluations.
Vertical offset of second buffer ?
This entry allows a vertical displacement of the second buffer relative to
the first. If the cell in the first buffer is centred on pixel (ix,jy),
then the cell in the second buffer is centred on pixel (ix+ixOff,jy+jyOff)
where ixOff is the offset (positive or negative) specified by this entry.
The correlation value will be plotted at the (ix+ixOff,jy+jyOff) pixel to
allow multiple different offsets to be plotted on the same buffer (provided
the spacing of the function evaluation is sufficiently far apart).
Horizontal offset of second buffer ?
This entry allows a horizontal displacement of the second buffer relative
to the first. If the cell in the first buffer is centred on pixel (ix,jy),
then the cell in the second buffer is centred on pixel (ix+ixOff,jy+jyOff)
where jyOff is the offset (positive or negative) specified by this entry.
The correlation value will be plotted at the (ix+ixOff,jy+jyOff) pixel to
allow multiple different offsets to be plotted on the same buffer (provided
the spacing of the function evaluation is sufficiently far apart).
Cross correlation in Window or whole Screen ?
The cross correlation function may be evaluated either within a window
(<W>) or the entire buffer (<S>). In either case, if an offset is used for
the second window, the region over which the correlation is evaluated is
reduced to ensure that all of both the source cells are entirely within the
buffer.
Window Selection: Region to cross correlate
If correlation within a window is selected, then the normal DigImage window
selection submenu will be produced to enable interactive window
specification. For more information on window specification, refer to the
[H Help] facility within the submenu.
Parent menu
Main Menu
DigImage User Documentation
Stuart Dalziel,
last page update: 19 February 1996