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fix(qfactor): correct 1/√2 offset scaling and LL-band visual weight #437

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Merged
osamu620 merged 2 commits into from
Jun 18, 2026
Merged

fix(qfactor): correct 1/√2 offset scaling and LL-band visual weight #437

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6fb6650
fix(qfactor): correct 1/sqrt(2) offset scaling and LL-band visual weight
osamu620 Jun 17, 2026
a288fec
refactor(qfactor): drop dead qfactor==0xFF branch in QCD step-size calc
osamu620 Jun 18, 2026
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7 changes: 4 additions & 3 deletions source/apps/estimate_qfactor/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -282,13 +282,14 @@ std::vector<Band> predict_bands(uint8_t qfactor, uint8_t dwt_levels, uint8_t RI,
alpha_Q = alpha_T1 * std::pow(alpha_T0 / alpha_T1, qpower);
}
const double eps0 = std::sqrt(0.5) / static_cast<double>(1u << RI);
const double delta_Q = alpha_Q * M_Q;
const double delta_ref = delta_Q * G_c_sqrt[0] + eps0;
const double delta_Q = alpha_Q * M_Q + eps0;
const double delta_ref = delta_Q * G_c_sqrt[0];
const double G_c = G_c_sqrt[Cqcc];

std::vector<Band> out(num_bands);
for (size_t i = 0; i < num_bands; ++i) {
double w_b = (i >= weights.size()) ? 1.0 : std::pow(weights[i], qpower);
// LL band (last entry, always weight 1.0) and any extra low-freq bands beyond the 5-level table
double w_b = (i == num_bands - 1 || i >= weights.size()) ? 1.0 : std::pow(weights[i], qpower);
double fval = delta_ref / (std::sqrt(wmse[i]) * w_b * G_c);
int32_t exponent = 0;
while (fval < 1.0) {
Expand Down
23 changes: 13 additions & 10 deletions source/core/codestream/j2kmarkers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -835,17 +835,18 @@ QCD_marker::QCD_marker(uint8_t number_of_guardbits, uint8_t dwt_levels, uint8_t
}

const double eps0 = sqrt(0.5) / static_cast<double>(1 << RI);
double delta_Q = alpha_Q * M_Q;
double delta_ref = delta_Q * G_c_sqrt[0] + eps0;
double delta_Q = alpha_Q * M_Q + eps0;
double delta_ref = delta_Q * G_c_sqrt[0];
double G_c = G_c_sqrt[0]; // gain of color transform
for (size_t i = 0; i < epsilon.size(); ++i) {
int32_t exponent, mantissa;
double w_b;
// w_b for LL band shall be 1.0
w_b = (i >= W_b_Y.size()) ? 1.0 : pow(W_b_Y[i], qfactor_power);
// w_b for the LL band (always the last entry) shall be 1.0, as must any extra
// low-frequency bands beyond the 5-level table when dwt_levels > 5.
w_b = (i == epsilon.size() - 1 || i >= W_b_Y.size()) ? 1.0 : pow(W_b_Y[i], qfactor_power);

double fval = (qfactor != 0xFF) ? delta_ref / (sqrt(wmse_or_BIBO[i]) * w_b * G_c)
: basestep / sqrt(wmse_or_BIBO[i]);
// qfactor == 0xFF is handled by the branch above, so it is always != 0xFF here.
double fval = delta_ref / (sqrt(wmse_or_BIBO[i]) * w_b * G_c);
for (exponent = 0; fval < 1.0; exponent++) {
fval *= 2.0;
}
Expand Down Expand Up @@ -1139,15 +1140,17 @@ QCC_marker::QCC_marker(uint16_t Csiz, uint16_t c, uint8_t number_of_guardbits, u
}

const double eps0 = sqrt(0.5) / static_cast<double>(1 << RI);
double delta_Q = alpha_Q * M_Q;
double delta_ref = delta_Q * G_c_sqrt[0] + eps0;
double delta_Q = alpha_Q * M_Q + eps0;
double delta_ref = delta_Q * G_c_sqrt[0];
double G_c = G_c_sqrt[Cqcc]; // gain of color transform

for (size_t i = 0; i < epsilon.size(); ++i) {
int32_t exponent, mantissa;
double w_b;
// w_b for LL band shall be 1.0
w_b = (i >= W_b_sqrt[Cqcc].size()) ? 1.0 : pow(W_b_sqrt[Cqcc][i], qfactor_power);
// w_b for the LL band (always the last entry) shall be 1.0, as must any extra
// low-frequency bands beyond the 5-level table when dwt_levels > 5.
w_b = (i == epsilon.size() - 1 || i >= W_b_sqrt[Cqcc].size()) ? 1.0
: pow(W_b_sqrt[Cqcc][i], qfactor_power);

double fval = delta_ref / (sqrt(wmse_or_BIBO[i]) * w_b * G_c);
for (exponent = 0; fval < 1.0; exponent++) {
Expand Down