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RadiancePmap/rgbecontrib.h
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rgbecontrib.h
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/*
=========================================================================
Reduced RGBE representation of normalised coefficients. Per default, this
consists of three signed 5-bit mantissas for each RGB colour channel and
a common 5-bit exponent (= 20 bits). This allocation can be modified
within a 32-bit envelope if more precision is required.
The floating point RGB contributions are assumed to lie in the range
[-1, 1], with values in the interval [-RGBE_CONTRIB_MIN,
RGBE_CONTRIB_MIN] clamped to 0, since these cannot be resolved.
The encoded values are therefore normalised against a given normalisation
factor (e.g. absolute maximum) in order to maximise the useful range.
Roland Schregle (roland.schregle@{hslu.ch, gmail.com})
(c) Lucerne University of Applied Sciences and Arts,
supported by the Swiss National Science Foundation
(SNSF #179067, "Light Fields for Spatio-Temporal Glare Assessment")
=========================================================================
$Id$
*/
#ifndef _RGBE_CONTRIB_H
#define _RGBE_CONTRIB_H
#include <stdint.h>
/* RGBE Mantissa / exponent / bin bits and their encoding ranges
(NOTE: The binary shifts can overflow if the number of bits is
increased; in this case the much slower pow(2, ..) can be used. */
#define RGBE_CONTRIB_MANTBITS 5
#define RGBE_CONTRIB_EXPBITS 5
#define RGBE_CONTRIB_BINBITS 12
/* Signed maximum for mantissa */
#define RGBE_CONTRIB_MANTMAX (1 << (RGBE_CONTRIB_MANTBITS - 1))
/* Absolute overflow limit for mantissa (sign flips if exceeded) */
#define RGBE_CONTRIB_MANTOVF ((RGBE_CONTRIB_MANTMAX << 1) - 1)
#define RGBE_CONTRIB_MIN (1.0 / (1L << (1 << RGBE_CONTRIB_EXPBITS)))
#define RGBE_CONTRIB_MAX 1.0
#define RGBE_CONTRIB_BINMAX ((1U << RGBE_CONTRIB_BINBITS) - 1)
typedef union {
struct {
/* Compressed RGBE representation of binned contributions,
* consisting of a 4-bit mantissa + sign per RGB, a common 5-bit
* exponent, and a 12-bit bin number. */
unsigned red: RGBE_CONTRIB_MANTBITS,
grn: RGBE_CONTRIB_MANTBITS,
blu: RGBE_CONTRIB_MANTBITS,
exp: RGBE_CONTRIB_EXPBITS,
bin: RGBE_CONTRIB_BINBITS;
};
uint32_t rgbeBin;
} RGBEContrib;
RGBEContrib RGBEContribEnc (
double rgb [3], double norm [3], unsigned bin
);
/* Normalise signed float RGB contributions against abs(norm), and encode
* to RGBE with associated bin. Issues warning if abs(norm) < abs(rgb). */
unsigned RGBEContribDec (
RGBEContrib rgbeCont, double norm [3], double rgb [3]
);
/* Decode RGBE contribution, returning signed floating point contributions
* in array rgb after denormalisation against abs(norm), and the associated
* bin as return value. */
#endif
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