vips_merge ()

int
vips_merge (VipsImage *ref,
            VipsImage *sec,
            VipsImage **out,
            VipsDirection direction,
            int dx,
            int dy,
            ...);

Optional arguments:

mblend : maximum blend size

This operation joins two images left-right (with ref on the left) or up-down (with ref above) with a smooth seam.

If the number of bands differs, one of the images must have one band. In this case, an n-band image is formed from the one-band image by joining n copies of the one-band image together, and then the two n-band images are operated upon.

The two input images are cast up to the smallest common type (see table Smallest common format in

dx and dy give the displacement of sec relative to ref , in other words, the vector to get from the origin of sec to the origin of ref , in other words, dx will generally be a negative number.

mblend limits the maximum width of the blend area. A value of "-1" means "unlimited". The two images are blended with a raised cosine.

Pixels with all bands equal to zero are "transparent", that is, zero pixels in the overlap area do not contribute to the merge. This makes it possible to join non-rectangular images.

See also: vips_mosaic(), vips_insert().

vips_mosaic ()

int
vips_mosaic (VipsImage *ref,
             VipsImage *sec,
             VipsImage **out,
             VipsDirection direction,
             int xref,
             int yref,
             int xsec,
             int ysec,
             ...);

Optional arguments:

bandno : band to search for features hwindow : half window size harea : half search size mblend : maximum blend size

This operation joins two images left-right (with ref on the left) or top-bottom (with ref above) given an approximate overlap.

sec is positioned so that the pixel (xsec , ysec ) lies on top of the pixel in ref at (xref , yref ). The overlap area is divided into three sections, 20 high-contrast points in band bandno of image ref are found in each, and each high-contrast point is searched for in sec using hwindow and harea (see vips_correl()).

A linear model is fitted to the 60 tie-points, points a long way from the fit are discarded, and the model refitted until either too few points remain or the model reaches good agreement.

The detected displacement is used with vips_merge() to join the two images together.

See also: vips_merge(), vips_insert().

vips_mosaic1 ()

int
vips_mosaic1 (VipsImage *ref,
              VipsImage *sec,
              VipsImage **out,
              VipsDirection direction,
              int xr1,
              int yr1,
              int xs1,
              int ys1,
              int xr2,
              int yr2,
              int xs2,
              int ys2,
              ...);

Optional arguments:

search : search to improve tie-points hwindow : half window size harea : half search size interpolate : interpolate pixels with this mblend : maximum blend size bandno : band to search for features

This operation joins two images top-bottom (with sec on the right) or left-right (with sec at the bottom) given an approximate pair of tie-points. sec is scaled and rotated as necessary before the join.

Before performing the transformation, the tie-points are improved by searching band bandno in an area of sec of size hsearchsize for a match of size hwindowsize to ref .

If search is TRUE, before performing the transformation, the tie-points are improved by searching an area of sec of size harea for a mosaic1 of size hwindow to ref .

mblend limits the maximum size of the blend area. A value of "-1" means "unlimited". The two images are blended with a raised cosine.

Pixels with all bands equal to zero are "transparent", that is, zero pixels in the overlap area do not contribute to the merge. This makes it possible to join non-rectangular images.

If the number of bands differs, one of the images must have one band. In this case, an n-band image is formed from the one-band image by joining n copies of the one-band image together, and then the two n-band images are operated upon.

The two input images are cast up to the smallest common type (see table Smallest common format in

See also: vips_merge(), vips_insert(), vips_globalbalance().

vips_match ()

int
vips_match (VipsImage *ref,
            VipsImage *sec,
            VipsImage **out,
            int xr1,
            int yr1,
            int xs1,
            int ys1,
            int xr2,
            int yr2,
            int xs2,
            int ys2,
            ...);

Optional arguments:

search : search to improve tie-points hwindow : half window size harea : half search size interpolate : interpolate pixels with this

Scale, rotate and translate sec so that the tie-points line up.

If search is TRUE, before performing the transformation, the tie-points are improved by searching an area of sec of size harea for a match of size hwindow to ref .

This function will only work well for small rotates and scales.

vips_globalbalance ()

int
vips_globalbalance (VipsImage *in,
                    VipsImage **out,
                    ...);

Optional arguments:

gamma : gamma of source images int_output : TRUE for integer image output

vips_globalbalance() can be used to remove contrast differences in an assembled mosaic.

It reads the History field attached to in and builds a list of the source images that were used to make the mosaic and the position that each ended up at in the final image.

It opens each of the source images in turn and extracts all parts which overlap with any of the other images. It finds the average values in the overlap areas and uses least-mean-square to find a set of correction factors which will minimise overlap differences. It uses gamma to gamma-correct the source images before calculating the factors. A value of 1.0 will stop this.

Each of the source images is transformed with the appropriate correction factor, then the mosaic is reassembled. out is VIPS_FORMAT_FLOAT, but if int_output is set, the output image is the same format as the input images.

There are some conditions that must be met before this operation can work: the source images must all be present under the filenames recorded in the history on in , and the mosaic must have been built using only operations in this package.

See also: vips_remosaic().

vips_remosaic ()

int
vips_remosaic (VipsImage *in,
               VipsImage **out,
               const char *old_str,
               const char *new_str,
               ...);

vips_remosaic() works rather as vips_globalbalance(). It takes apart the mosaiced image in and rebuilds it, substituting images.

Unlike vips_globalbalance(), images are substituted based on their file‐ names. The rightmost occurence of the string old_str is swapped for new_str , that file is opened, and that image substituted for the old image.

It's convenient for multispectral images. You can mosaic one band, then use that mosaic as a template for mosaicing the others automatically.

See also: vips_globalbalance().

im_correl ()

int
im_correl (VipsImage *ref,
           VipsImage *sec,
           int xref,
           int yref,
           int xsec,
           int ysec,
           int hwindowsize,
           int hsearchsize,
           double *correlation,
           int *x,
           int *y);

This operation finds the position of sec within ref .

The area around (xsec , ysec ) is searched for the best match to the area around (xref , yref ). It searches an area of size hsearchsize for a match of size hwindowsize . The position of the best match is returned, together with the correlation at that point.

Only the first band of each image is correlated. ref and sec may be very large --- the function extracts and generates just the parts needed. Correlation is done with im_spcor(); the position of the maximum is found with im_maxpos().

See also: im_match_linear(), im_match_linear_search(), im_lrmosaic().

im_align_bands ()

int
im_align_bands (VipsImage *in,
                VipsImage *out);

This operation uses im_phasecor_fft() to find an integer displacement to align all image bands band 0. It is very slow and not very accurate.

Use im_estpar() in preference: it's fast and accurate.

See also: im_global_balancef(), im_remosaic().

im_maxpos_subpel ()

int
im_maxpos_subpel (VipsImage *in,
                  double *x,
                  double *y);

This function implements:

"Extension of Phase Correlation to Subpixel Registration" by H. Foroosh, from IEEE trans. Im. Proc. 11(3), 2002.

If the best three matches in the correlation are aranged:

02 or 01 1 2

then we return a subpixel match using the ratio of correlations in the vertical and horizontal dimension.

( xs[0], ys[0] ) is the best integer alignment ( xs[ use_x ], ys[ use_x ] ) is equal in y and (+/-)1 off in x ( xs[ use_y ], ys[ use_y ] ) is equal in x and (+/-)1 off in y

Alternatively if the best four matches in the correlation are aranged in a square:

01 or 03 or 02 or 03 32 12 31 21

then we return a subpixel match weighting with the sum the two on each side over the sum of all four, but only if all four of them are very close to the best, and the fifth is nowhere near.

This alternative method is not described by Foroosh, but is often the case where the match is close to n-and-a-half pixels in both dimensions.

See also: im_maxpos(), im_min(), im_stats().