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