| .TH IM_GLOBAL_BALANCE 3 "13 May 1991" |
| .SH NAME |
| im_global_balance, im_global_balancef \- perform global mosaic balancing on |
| an image |
| .SH SYNOPSIS |
| #include <vips/vips.h> |
| |
| int |
| .br |
| im_global_balance( IMAGE *in, IMAGE *out, double gamma ) |
| |
| int |
| .br |
| im_global_balance_float( IMAGE *in, IMAGE *out, double gamma ) |
| |
| .SH DESCRIPTION |
| These functions takes an image assembled with the mosaicing functions |
| (im_*merge*(), im_*mosaic*()), take it apart, and reassemble it, globally |
| optimising the image balance. This is useful for assembling image mosaics |
| from sources where the exposure is uncontrolled and may vary from tile to tile |
| --- such as video, or photographic sources. |
| |
| The function finds a set of factors, one for each of the input images, and |
| scales each image by its factor before reassembling. The factors are chosen so |
| as to minimise the average grey-level difference between neighboring images at |
| their overlaps. Trivial overlaps (where the width and height of the overlap |
| are both less than 20 pixels) are ignored. |
| |
| The gamma parameter is the gamma of the image input system. It is used during |
| brightness adjustment. Set to 1.0 to disable gamma, to 1.6 for a typical IR |
| vidicon camera, or 2.3 for a typical video camera. |
| |
| It relies on information left by the mosaicing functions in ".desc" files. If |
| the ".desc" file of the input image has been corrupted, or is strangely |
| complicated, or if any of the original input images have been moved or |
| deleted, the function can fail. |
| |
| The function will fail for mosaics larger than about 7 by 7 frames, since it |
| will run out of file descriptors (UNIX sets a limit of 256 per process). To |
| balance larger mosaics, just assemble them in 7x7 sections, balancing and |
| saving each part in turn, before loading, assembling and balancing the final |
| image. The function can also fail if there are significant mosaicing errors. |
| |
| im_global_balancef() works as im_global_balance(), but outputs a float |
| rather than a uchar image. This lets you adjust the range of the image |
| manually, if the automatically-found scales are causing burn-out. |
| |
| .SH RETURN VALUE |
| All functions return 0 on success and -1 on error. |
| .SH SEE ALSO |
| im_lrmerge(3), im_lrmosaic(3). |
| .SH COPYRIGHT |
| Birkbeck College and the National Gallery, 1991 - 1995. |
