// NOTE : Also seems not well written and craves optimization at places. P.A.N.A.R.G.O.
// => frame = 8 bit greyscale CvMat
static public void ContrastEnhancement(CvMat frame)
{
//CvMat originalFrame = frame; // return this if cannot enhance
//if (frame.ElemType != MatrixType.U8C1)
// frame = MatOps.Convert(frame, MatrixType.U8C1, 1 / 255.0 );
/////original histogram
const int HistBinSize = 256;
int[] histSizes = new int[1];
histSizes[0] = HistBinSize;
CvHistogram hist = new CvHistogram(histSizes, HistogramFormat.Array);
Cv.CalcArrHist(frame, hist, false); // size = 256 implied
CvHistogram newHist = MatOps.CopyHistogram(hist);
CvArr newHistBin = newHist.Bins;
//double[] origVals = new double[hist.Bins.GetDims( 0 )];
List <double> origVals = new List <double>(HistBinSize);
for (int i = 0; i < HistBinSize; i++)
{
double elem = newHistBin.GetReal1D(i);
if (elem != 0)
{
origVals.Add(elem);
}
}
// FIX : See no need for histL, since we have origVals
//////histogram with only nonzero bins
//CvMat histL = new CvMat( imageRows, imageCols, MatrixType.F32C1, new CvScalar( 0 ) );
//for (i = 0; i < origVals.size(); i++)
// histL.at<float>( i, 0 ) = origVals.at( i );
List <double> peakValues = new List <double>(HistBinSize); //std::vector<int> peakValues;
//////////3 bin search window
for (int i = 1; i < origVals.Count - 2; ++i)
{
double elem = origVals[i];
if (elem > origVals[i - 1] && elem > origVals[i + 1])
{
peakValues.Add(elem);
}
}
if (peakValues.Count == 0)
{
//Console.Out.WriteLine( "Cannot enhance" );
return; // cannot enhance?
}
//////Upper threshold
double threshUP = 0;
for (int i = 0; i < peakValues.Count; ++i)
{
threshUP += peakValues[i];
}
threshUP /= peakValues.Count;
//////Lower threshold
double threshDOWN = Math.Min((frame.Cols * frame.Rows), threshUP * origVals.Count) / 256.0;
//Console.Out.WriteLine( "Enhance thresholds " + threshUP + "/" + threshDOWN );
//////histogram reconstruction
CvArr histBins = hist.Bins;
for (int i = 0; i < HistBinSize; ++i)
{
double histElem = histBins.GetReal1D(i);
if (histElem > threshUP)
{
histBins.SetReal1D(i, threshUP);
}
else if (histElem <= threshUP && histElem >= threshDOWN)
{
continue;
}
else if (histElem < threshDOWN && histElem > 0)
{
histBins.SetReal1D(i, threshDOWN);
}
else if (histElem == 0)
{
continue;
}
}
// accumulated values(?)
double[] accVals = new double[HistBinSize]; //std::vector<int> accVals;
accVals[0] = (histBins.GetReal1D(0));
for (int i = 1; i < HistBinSize; ++i)
{
accVals[i] = (accVals[i - 1] + histBins[i]);
}
byte[] lookUpTable = new byte[HistBinSize]; //cv::Mat lookUpTable = cv::Mat::zeros( hist.size(), CV_8UC1 );
for (int i = 0; i < HistBinSize; ++i)
{
lookUpTable[i] = (byte)(255.0 * accVals[i] / accVals[255]);
}
// assign computed values to input frame
//Console.Out.Write( "Enhance-->" );
for (int i = 0; i < frame.Cols; ++i)
{
for (int j = 0; j < frame.Rows; ++j)
{
// there is NO mask, thus no need to check for; was: "if (mask.data)..."
byte oldValue = (byte)frame.Get2D(j, i);
byte newValue = lookUpTable[oldValue];
//if ((newValue <1 || newValue > 254) && (newValue != oldValue)) Console.Out.Write( oldValue + " " + newValue + "|");
frame.Set2D(j, i, newValue);
//frame.SetReal2D( j, i, lookUpTable[ (int)(255.0 * frame.GetReal2D( j, i )) ] / 255.0);
}
}
//Console.Out.WriteLine();
//frame = MatOps.Convert( frame, MatrixType.U8C1, 255.0 );
}
