libvips/libvips/colour/sRGB2HSV.c

/* to HSV ... useful for compatibility with other packages
 *
 * 9/6/15
 * 	- from LabS2Lab.c
 */

/*

    This file is part of VIPS.
    
    VIPS is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    02110-1301  USA

 */

/*

    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk

 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <glib/gi18n-lib.h>

#include <stdio.h>

#include <vips/vips.h>

#include "pcolour.h"

typedef VipsColourCode VipssRGB2HSV;
typedef VipsColourCodeClass VipssRGB2HSVClass;

G_DEFINE_TYPE( VipssRGB2HSV, vips_sRGB2HSV, VIPS_TYPE_COLOUR_CODE );

static void
vips_sRGB2HSV_line( VipsColour *colour, VipsPel *out, VipsPel **in, int width )
{
	unsigned char *p = (unsigned char *) in[0];
	unsigned char *q = (unsigned char *) out;

	int i;

	for( i = 0; i < width; i++ ) {
		unsigned char c_max;
		unsigned char c_min;
		float secondary_diff;
		float wrap_around_hue;

		if( p[1] < p[2] ) {
			if( p[2] < p[0] ) {
				/* Center red (at top).
				 */
				c_max = p[0];
				c_min = p[1];
				secondary_diff = p[1] - p[2];
				wrap_around_hue = 255.0;
			} 
			else {
				/* Center blue.
				 */
				c_max = p[2];
				c_min = VIPS_MIN( p[1], p[0] );
				secondary_diff = p[0] - p[1];
				wrap_around_hue = 170.0;
			}
		} 
		else {
			if( p[1] < p[0] ) {
				/* Center red (at bottom)
				 */
				c_max = p[0];
				c_min = p[2];
				secondary_diff = p[1] - p[2];
				wrap_around_hue = 0.0;
			} 
			else {
				/* Center green
				 */
				c_max = p[1];
				c_min = VIPS_MIN( p[2], p[0] );
				secondary_diff = p[2] - p[0];
				wrap_around_hue = 85.0;
			}
		}


		if( c_max == 0 ) {
			q[0] = 0;
			q[1] = 0;
			q[2] = 0;
		} 
		else {
			unsigned char delta;

			q[2] = c_max;
			delta = c_max - c_min;

			if( delta == 0 ) 
				q[0] = 0;
			else 
				q[0] = 42.5 * (secondary_diff / (float) delta) +
				       	wrap_around_hue;

			q[1] = delta * 255.0 / (float) c_max;
		}

		p += 3;
		q += 3;
	}
}

static void
vips_sRGB2HSV_class_init( VipssRGB2HSVClass *class )
{
	VipsObjectClass *object_class = (VipsObjectClass *) class;
	VipsColourClass *colour_class = VIPS_COLOUR_CLASS( class );

	object_class->nickname = "sRGB2HSV";
	object_class->description = _( "transform sRGB to HSV" );

	colour_class->process_line = vips_sRGB2HSV_line;
}

static void
vips_sRGB2HSV_init( VipssRGB2HSV *sRGB2HSV )
{
	VipsColour *colour = VIPS_COLOUR( sRGB2HSV );
	VipsColourCode *code = VIPS_COLOUR_CODE( sRGB2HSV );

	colour->interpretation = VIPS_INTERPRETATION_HSV;
	colour->format = VIPS_FORMAT_UCHAR;
	colour->bands = 3;
	colour->input_bands = 3;

	code->input_coding = VIPS_CODING_NONE;
	code->input_format = VIPS_FORMAT_UCHAR;
	code->input_interpretation = VIPS_INTERPRETATION_sRGB;
}

/**
 * vips_sRGB2HSV: (method)
 * @in: input image
 * @out: (out): output image
 * @...: %NULL-terminated list of optional named arguments
 *
 * Convert to HSV.
 *
 * HSV is a crude polar coordinate system for RGB images. It is provided for
 * compatibility with other image processing systems. See vips_Lab2LCh() for a 
 * much better colour space.
 *
 * See also: vips_HSV2sRGB(), vips_Lab2LCh().
 *
 * Returns: 0 on success, -1 on error.
 */
int
vips_sRGB2HSV( VipsImage *in, VipsImage **out, ... )
{
	va_list ap;
	int result;

	va_start( ap, out );
	result = vips_call_split( "sRGB2HSV", ap, in, out );
	va_end( ap );

	return( result );
}