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Fix rgbe conversion routines thanks to Charles Bloom. http://cbloomrants.blogspot.com/2020/06/widespread-error-in-radiance-hdr-rgbe.html

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This commit is contained in:
Ignacio 2020-06-07 19:46:35 -07:00
parent 3e034d2de1
commit 0f98a936f8
1 changed files with 11 additions and 10 deletions
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21
src/nvmath/PackedFloat.cpp
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@ -25,24 +25,25 @@ Vector3 nv::r11g11b10_to_vector3(FloatR11G11B10 v) {
FloatR11G11B10 nv::vector3_to_r11g11b10(const Vector3 & v) { FloatR11G11B10 nv::vector3_to_r11g11b10(const Vector3 & v) {
} }
// These are based on: // Implementation based on on:
// http://www.graphics.cornell.edu/~bjw/rgbe/rgbe.c // https://cbloomrants.blogspot.com/2020/06/widespread-error-in-radiance-hdr-rgbe.html
// While this may not be the best way to encode/decode RGBE8, I'm not making any changes to maintain compatibility.
FloatRGBE8 nv::vector3_to_rgbe8(const Vector3 & v) { FloatRGBE8 nv::vector3_to_rgbe8(const Vector3 & v) {
float m = max3(v.x, v.y, v.z); float m = max3(v.x, v.y, v.z);
FloatRGBE8 rgbe; FloatRGBE8 rgbe;
if (m < 1e-32) { if (m < 1e-32f) {
// Exponent byte = 0 is a special encoding that makes RGB output = 0
rgbe.v = 0; rgbe.v = 0;
} }
else { else {
int e; int e;
float scale = frexpf(m, &e) * 256.0f / m; frexpf(m, &e);
rgbe.r = U8(ftoi_round(v.x * scale)); float scale = ldexpf(1.0f, -exponent + 8);
rgbe.g = U8(ftoi_round(v.y * scale)); rgbe.r = U8(v.x * scale);
rgbe.b = U8(ftoi_round(v.z * scale)); rgbe.g = U8(v.y * scale);
rgbe.b = U8(v.z * scale);
rgbe.e = U8(e + 128); rgbe.e = U8(e + 128);
} }
@ -52,8 +53,8 @@ FloatRGBE8 nv::vector3_to_rgbe8(const Vector3 & v) {
Vector3 nv::rgbe8_to_vector3(FloatRGBE8 v) { Vector3 nv::rgbe8_to_vector3(FloatRGBE8 v) {
if (v.e != 0) { if (v.e != 0) {
float scale = ldexpf(1.0f, v.e-(int)(128+8)); // +8 to divide by 256. @@ Shouldn't we divide by 255 instead? float scale = ldexpf(1.0f, (int)v.e-128+8); // +8 to divide by 256.
return scale * Vector3(float(v.r), float(v.g), float(v.b)); return scale * Vector3(float(v.r + 0.5f), float(v.g + 0.5f), float(v.b + 0.5f));
} }
return Vector3(0); return Vector3(0);