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Avoid div by zero with test for bad chromaticities in RGBtoXYZ #1153

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merged 3 commits into from
Sep 24, 2021
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Avoid div by zero with test for bad chromaticities in RGBtoXYZ #1153

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936301b
stop div by zero by catching bad chromaticities
peterhillman Sep 22, 2021
8872bf6
add include to ImfChromaticities for new exception
peterhillman Sep 22, 2021
ca289ef
better detection of division by zero
peterhillman Sep 24, 2021
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42 changes: 35 additions & 7 deletions src/lib/OpenEXR/ImfChromaticities.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,9 @@
#include "ImfNamespace.h"
#include <string.h>

#include <stdexcept>
#include <float.h>

#if defined(_MSC_VER)
// suppress warning about non-exported base classes
#pragma warning (disable : 4251)
Expand Down Expand Up @@ -66,34 +69,59 @@ RGBtoXYZ (const Chromaticities &chroma, float Y)
// X and Z values of RGB value (1, 1, 1), or "white"
//

// prevent a division that rounds to zero
if (abs(chroma.white.y) <= 1.f && abs(chroma.white.x * Y) >= abs(chroma.white.y) * FLT_MAX)
{
throw std::invalid_argument("Bad chromaticities: white.y cannot be zero");
}

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How about:

Suggested change
if (abs(chroma.white.y) <= 1 && abs(chroma.white.x*Y) >= abs(chroma.white.y) * FLT_MAX)
throw std::invalid_argument("Bad chromaticities: white.y cannot be zero")

float X = chroma.white.x * Y / chroma.white.y;
float Z = (1 - chroma.white.x - chroma.white.y) * Y / chroma.white.y;

//
// Scale factors for matrix rows
// Scale factors for matrix rows, compute numerators and common denominator
//

float d = chroma.red.x * (chroma.blue.y - chroma.green.y) +
chroma.blue.x * (chroma.green.y - chroma.red.y) +
chroma.green.x * (chroma.red.y - chroma.blue.y);

float Sr = (X * (chroma.blue.y - chroma.green.y) -


float SrN = (X * (chroma.blue.y - chroma.green.y) -
chroma.green.x * (Y * (chroma.blue.y - 1) +
chroma.blue.y * (X + Z)) +
chroma.blue.x * (Y * (chroma.green.y - 1) +
chroma.green.y * (X + Z))) / d;
chroma.green.y * (X + Z)));


float Sg = (X * (chroma.red.y - chroma.blue.y) +
float SgN = (X * (chroma.red.y - chroma.blue.y) +
chroma.red.x * (Y * (chroma.blue.y - 1) +
chroma.blue.y * (X + Z)) -
chroma.blue.x * (Y * (chroma.red.y - 1) +
chroma.red.y * (X + Z))) / d;
chroma.red.y * (X + Z)));

float Sb = (X * (chroma.green.y - chroma.red.y) -
float SbN = (X * (chroma.green.y - chroma.red.y) -
chroma.red.x * (Y * (chroma.green.y - 1) +
chroma.green.y * (X + Z)) +
chroma.green.x * (Y * (chroma.red.y - 1) +
chroma.red.y * (X + Z))) / d;
chroma.red.y * (X + Z)));


if ( abs(d)<1.f && (abs(SrN) >= abs(d)* FLT_MAX || abs(SgN) >= abs(d)* FLT_MAX || abs(SbN) >= abs(d)* FLT_MAX) )
{
// cannot generate matrix if all RGB primaries have the same y value
// or if they all have the an x value of zero
// in both cases, the primaries are colinear, which makes them unusable
throw std::invalid_argument("Bad chromaticities: RGBtoXYZ matrix is degenerate");
}



float Sr = SrN / d;
float Sg = SgN / d;
float Sb = SbN / d;


//
// Assemble the matrix
Expand Down