diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/ipa/libipa/histogram.cpp | 39 |
1 files changed, 25 insertions, 14 deletions
diff --git a/src/ipa/libipa/histogram.cpp b/src/ipa/libipa/histogram.cpp index ea042f0a..bcf26390 100644 --- a/src/ipa/libipa/histogram.cpp +++ b/src/ipa/libipa/histogram.cpp @@ -149,26 +149,37 @@ double Histogram::quantile(double q, uint32_t first, uint32_t last) const double Histogram::interQuantileMean(double lowQuantile, double highQuantile) const { ASSERT(highQuantile > lowQuantile); - /* Proportion of pixels which lies below lowQuantile */ - double lowPoint = quantile(lowQuantile); - /* Proportion of pixels which lies below highQuantile */ - double highPoint = quantile(highQuantile, static_cast<uint32_t>(lowPoint)); - double sumBinFreq = 0, cumulFreq = 0; - - for (double p_next = floor(lowPoint) + 1.0; - p_next <= ceil(highPoint); - lowPoint = p_next, p_next += 1.0) { - int bin = floor(lowPoint); + + /* Proportion of pixels which lies below lowQuantile and highQuantile. */ + const double lowPoint = quantile(lowQuantile); + const double highPoint = quantile(highQuantile, static_cast<uint32_t>(lowPoint)); + + double sumBinFreq = 0; + double cumulFreq = 0; + + /* + * Calculate the mean pixel value between the low and high points by + * summing all the pixels between the two points, and dividing the sum + * by the number of pixels. Given the discrete nature of the histogram + * data, the sum of the pixels is approximated by accumulating the + * product of the bin values (calculated as the mid point of the bin) by + * the number of pixels they contain, for each bin in the internal. + */ + for (unsigned bin = std::floor(lowPoint); bin < std::ceil(highPoint); bin++) { + const double lowBound = std::max<double>(bin, lowPoint); + const double highBound = std::min<double>(bin + 1, highPoint); + double freq = (cumulative_[bin + 1] - cumulative_[bin]) - * (std::min(p_next, highPoint) - lowPoint); + * (highBound - lowBound); /* Accumulate weighted bin */ - sumBinFreq += bin * freq; + sumBinFreq += (highBound + lowBound) / 2 * freq; + /* Accumulate weights */ cumulFreq += freq; } - /* add 0.5 to give an average for bin mid-points */ - return sumBinFreq / cumulFreq + 0.5; + + return sumBinFreq / cumulFreq; } } /* namespace ipa */ |