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/*
* $Id: RGBToGray.c 3177 2008-04-01 14:47:24Z karstenm $
*
* This file contains routines for converting an image from
* RBG representaion to a single band of gray shades.
*/
/*
* Copyright 1993, 1994 University of British Columbia
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
* the above copyright notice appears in all copies and that both that
* copyright notice and this permission notice appear in supporting
* documentation. UBC makes no representations about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*
* Author: Daniel Ko, UBC Laboratory for Computational Intelligence
*/
/* From the Vista library: */
#include "viaio/Vlib.h"
#include "viaio/mu.h"
#include "viaio/os.h"
#include "viaio/VImage.h"
/* From the standard C libaray: */
#include <math.h>
/* File identification string: */
VRcsId ("$Id: RGBToGray.c 3177 2008-04-01 14:47:24Z karstenm $");
/*
* VRGBImageToGray
*
* Combine the 3 bands of a RGB image into a single band of gray shades.
*/
VImage VRGBImageToGray (VImage src, VImage dest, VBand band)
{
int src_band, dest_nbands, dest_band, npixels, i;
/* Require a single-component RGB image: */
if (VImageNComponents (src) != 1 ||
VImageColorInterp (src) != VBandInterpRGB) {
VWarning ("VRGBImageToGray: Image isn't single-component RGB");
return NULL;
}
if (band == VAllBands) {
dest_nbands = VImageNBands (src) / 3;
src_band = 0;
} else if (band >= 0 && band + 2 < VImageNBands (src)) {
dest_nbands = 1;
src_band = band;
} else {
VWarning ("VRGBImageToGray: Band %d referenced in image of %d band(s)",
band, VImageNBands (src));
return NULL;
}
/* Create or check the destination image: */
dest = VSelectDestImage ("VRGBImageToGray", dest, dest_nbands,
VImageNRows (src), VImageNColumns (src),
VPixelRepn (src));
if (dest == NULL)
return NULL;
/*
* Take weighted average of the 3 bands:
*/
#define RGBToGray(type) \
{ \
type *rpixs = (type *) VPixelPtr (src, src_band, 0, 0); \
type *gpixs = (type *) VPixelPtr (src, src_band + 1, 0, 0); \
type *bpixs = (type *) VPixelPtr (src, src_band + 2, 0, 0); \
type *dest_pixels = (type *) VPixelPtr (dest, dest_band, 0, 0); \
for (i = 0; i < npixels; i++) \
*dest_pixels++ = 0.299 * *rpixs++ \
+ 0.587 * *gpixs++ \
+ 0.114 * *bpixs++; \
}
/* Perform pixel averaging according to pixel representation: */
npixels = VImageNRows (src) * VImageNColumns (src);
for (dest_band = 0; dest_band < dest_nbands; dest_band++, src_band += 3)
switch (VPixelRepn (src)) {
case VBitRepn: RGBToGray(VBit); break;
case VUByteRepn: RGBToGray(VUByte); break;
case VSByteRepn: RGBToGray(VSByte); break;
case VShortRepn: RGBToGray(VShort); break;
case VLongRepn: RGBToGray(VLong); break;
case VFloatRepn: RGBToGray(VFloat); break;
case VDoubleRepn: RGBToGray(VDouble); break;
default: break;
}
/* Adopt the band interpretation information from the source image but
delete any color interpretation: */
if (band == VAllBands) {
if (VImageAttrList (dest))
VDestroyAttrList (VImageAttrList (dest));
VImageAttrList (dest) = VCopyAttrList (VImageAttrList (src));
VExtractAttr (VImageAttrList (dest), VColorInterpAttr, NULL,
VBitRepn, NULL, FALSE);
VImageNFrames (dest) = VImageNFrames (src);
VImageNViewpoints (dest) = VImageNViewpoints (src);
VImageNColors (dest) = VImageNComponents (dest) = 1;
} else VCopyImageAttrs (src, dest);
return dest;
#undef RGBToGray
}
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