/// <summary>
/// This will adjust the histograms in the data, ensuring that no gradient angle bin has a value greater than one. The histograms will be adjusted based upon the largest magnitude
/// with a block of histograms - all magnitudes will be divided by the greatest magnitude of any angle within that block, such that no value anywhere will be greater than one
/// </summary>
public DataRectangle <HistogramOfGradient> Normalise(DataRectangle <HistogramOfGradient> hogs)
{
if (hogs == null)
{
throw new ArgumentNullException(nameof(hogs));
}
if ((hogs.Width < _blockSize) || (hogs.Height < _blockSize))
{
throw new ArgumentException($"too little data ({hogs.Width}x{hogs.Height}) for specified block size ({_blockSize})");
}
// For each overlapping block, we normalise and add the block contents to the normalisedHogs set. Blocks will be counted multiple times, which
// is why the returned DataRectangle is larger than the input one. For example, given a 3x2 rectangle of histograms, there are data cells -
//
// 1 2 3
// 4 5 6
//
// The normalised data will be four across because the first block to normalise will have histograms {{1,2},{4,5}} normalised and then the second block
// will have {{2,3},{5,6}} normalised. This means that we have two blocks of 2x2 which combine to create a new output rectangle that is 4x2. The middle
// elements (2 and 5) appear multiple times, which is expected.
var numberOfOverlappingBlocksAcross = hogs.Width - (_blockSize - 1);
var numberOfOverlappingBlocksDown = hogs.Height - (_blockSize - 1);
var normalisedHogs = new HistogramOfGradient[numberOfOverlappingBlocksAcross * _blockSize, numberOfOverlappingBlocksDown *_blockSize];
for (var x = 0; x < numberOfOverlappingBlocksAcross; x++)
{
for (var y = 0; y < numberOfOverlappingBlocksDown; y++)
{
var hogsInBlock = hogs.Slice(Rectangle.FromLTRB(
left: x,
right: x + _blockSize,
top: y,
bottom: y + _blockSize
));
var maxMagnitudeWithinBlock = hogsInBlock.Enumerate().Max(pointAndHog => pointAndHog.Item2.GreatestMagnitude);
var normalisedHogsInBlock = (maxMagnitudeWithinBlock == 0) // TODO: Need tests, particularly around this sort of thing
? hogsInBlock.Transform(hog => hog.Normalise())
: hogsInBlock.Transform(hog => hog.Multiply(1 / maxMagnitudeWithinBlock));
for (var i = 0; i < _blockSize; i++)
{
for (var j = 0; j < _blockSize; j++)
{
normalisedHogs[(x * _blockSize) + i, (y * _blockSize) + j] = normalisedHogsInBlock[i, j];
}
}
}
}
return(new DataRectangle <HistogramOfGradient>(normalisedHogs));
}
