static DoubleMatrix ClipContrast(BlockMap blocks, HistogramCube histogram)
{
var result = new DoubleMatrix(blocks.Primary.Blocks);
foreach (var block in blocks.Primary.Blocks.Iterate())
{
int volume = histogram.Sum(block);
int clipLimit = Doubles.RoundToInt(volume * Parameters.ClippedContrast);
int accumulator = 0;
int lowerBound = histogram.Bins - 1;
for (int i = 0; i < histogram.Bins; ++i)
{
accumulator += histogram[block, i];
if (accumulator > clipLimit)
{
lowerBound = i;
break;
}
}
accumulator = 0;
int upperBound = 0;
for (int i = histogram.Bins - 1; i >= 0; --i)
{
accumulator += histogram[block, i];
if (accumulator > clipLimit)
{
upperBound = i;
break;
}
}
result[block] = (upperBound - lowerBound) * (1.0 / (histogram.Bins - 1));
}
// https://sourceafis.machinezoo.com/transparency/contrast
FingerprintTransparency.Current.Log("contrast", result);
return(result);
}
static DoubleMatrix Equalize(BlockMap blocks, DoubleMatrix image, HistogramCube histogram, BooleanMatrix blockMask)
{
const double rangeMin = -1;
const double rangeMax = 1;
const double rangeSize = rangeMax - rangeMin;
double widthMax = rangeSize / histogram.Bins * Parameters.MaxEqualizationScaling;
double widthMin = rangeSize / histogram.Bins * Parameters.MinEqualizationScaling;
var limitedMin = new double[histogram.Bins];
var limitedMax = new double[histogram.Bins];
var dequantized = new double[histogram.Bins];
for (int i = 0; i < histogram.Bins; ++i)
{
limitedMin[i] = Math.Max(i * widthMin + rangeMin, rangeMax - (histogram.Bins - 1 - i) * widthMax);
limitedMax[i] = Math.Min(i * widthMax + rangeMin, rangeMax - (histogram.Bins - 1 - i) * widthMin);
dequantized[i] = i / (double)(histogram.Bins - 1);
}
var mappings = new Dictionary <IntPoint, double[]>();
foreach (var corner in blocks.Secondary.Blocks.Iterate())
{
double[] mapping = new double[histogram.Bins];
mappings[corner] = mapping;
if (blockMask.Get(corner, false) ||
blockMask.Get(corner.X - 1, corner.Y, false) ||
blockMask.Get(corner.X, corner.Y - 1, false) ||
blockMask.Get(corner.X - 1, corner.Y - 1, false))
{
double step = rangeSize / histogram.Sum(corner);
double top = rangeMin;
for (int i = 0; i < histogram.Bins; ++i)
{
double band = histogram[corner, i] * step;
double equalized = top + dequantized[i] * band;
top += band;
if (equalized < limitedMin[i])
{
equalized = limitedMin[i];
}
if (equalized > limitedMax[i])
{
equalized = limitedMax[i];
}
mapping[i] = equalized;
}
}
}
var result = new DoubleMatrix(blocks.Pixels);
foreach (var block in blocks.Primary.Blocks.Iterate())
{
var area = blocks.Primary.Block(block);
if (blockMask[block])
{
var topleft = mappings[block];
var topright = mappings[new IntPoint(block.X + 1, block.Y)];
var bottomleft = mappings[new IntPoint(block.X, block.Y + 1)];
var bottomright = mappings[new IntPoint(block.X + 1, block.Y + 1)];
for (int y = area.Top; y < area.Bottom; ++y)
{
for (int x = area.Left; x < area.Right; ++x)
{
int depth = histogram.Constrain((int)(image[x, y] * histogram.Bins));
double rx = (x - area.X + 0.5) / area.Width;
double ry = (y - area.Y + 0.5) / area.Height;
result[x, y] = Doubles.Interpolate(bottomleft[depth], bottomright[depth], topleft[depth], topright[depth], rx, ry);
}
}
}
else
{
for (int y = area.Top; y < area.Bottom; ++y)
{
for (int x = area.Left; x < area.Right; ++x)
{
result[x, y] = -1;
}
}
}
}
// https://sourceafis.machinezoo.com/transparency/equalized-image
FingerprintTransparency.Current.Log("equalized-image", result);
return(result);
}