opencv calcHistLookupTables_8u

opencv  calcHistLookupTables_8u

static void calcHistLookupTables_8u( const Mat& hist, const SparseMat& shist,
                         int dims, const float** ranges, const double* uniranges,
                         bool uniform, bool issparse, std::vector<size_t>& _tab )
{
    const int low = 0, high = 256;
    int i, j;
    _tab.resize((high-low)*dims);
    size_t* tab = &_tab[0];

    if( uniform )
    {
        for( i = 0; i < dims; i++ )
        {
            double a = uniranges[i*2];
            double b = uniranges[i*2+1];
            int sz = !issparse ? hist.size[i] : shist.size(i);
            size_t step = !issparse ? hist.step[i] : 1;

            for( j = low; j < high; j++ )
            {
                int idx = cvFloor(j*a + b);
                size_t written_idx;
                if( (unsigned)idx < (unsigned)sz )
                    written_idx = idx*step;
                else
                    written_idx = OUT_OF_RANGE;

                tab[i*(high - low) + j - low] = written_idx;
            }
        }
    }
    else if (ranges)
    {
        for( i = 0; i < dims; i++ )
        {
            int limit = std::min(cvCeil(ranges[i][0]), high);
            int idx = -1, sz = !issparse ? hist.size[i] : shist.size(i);
            size_t written_idx = OUT_OF_RANGE;
            size_t step = !issparse ? hist.step[i] : 1;

            for(j = low;;)
            {
                for( ; j < limit; j++ )
                    tab[i*(high - low) + j - low] = written_idx;

                if( (unsigned)(++idx) < (unsigned)sz )
                {
                    limit = std::min(cvCeil(ranges[i][idx+1]), high);
                    written_idx = idx*step;
                }
                else
                {
                    for( ; j < high; j++ )
                        tab[i*(high - low) + j - low] = OUT_OF_RANGE;
                    break;
                }
            }
        }
    }
    else
    {
        CV_Error(Error::StsBadArg, "Either ranges, either uniform ranges should be provided");
    }
}

代码参考：opencv-3.4.1modulesimgprocsrchistogram.cpp

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