/*
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For Open Source Computer Vision Library
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Copyright (C) 2015-2016, OpenCV Foundation, all rights reserved.
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*/
/*
Contributed by Gregor Kovalcik <gregor dot kovalcik at gmail dot com>
based on code provided by Martin Krulis, Jakub Lokoc and Tomas Skopal.
References:
Martin Krulis, Jakub Lokoc, Tomas Skopal.
Efficient Extraction of Clustering-Based Feature Signatures Using GPU Architectures.
Multimedia tools and applications, 75(13), pp.: 8071�8103, Springer, ISSN: 1380-7501, 2016
Christian Beecks, Merih Seran Uysal, Thomas Seidl.
Signature quadratic form distance.
In Proceedings of the ACM International Conference on Image and Video Retrieval, pages 438-445.
ACM, 2010.
*/
#include "../precomp.hpp"
#include "grayscale_bitmap.hpp"
namespace cv
{
namespace xfeatures2d
{
namespace pct_signatures
{
GrayscaleBitmap::GrayscaleBitmap(InputArray _bitmap, int bitsPerPixel)
: mBitsPerPixel(bitsPerPixel)
{
Mat bitmap = _bitmap.getMat();
if (bitmap.empty())
{
CV_Error(Error::StsBadArg, "Input bitmap is empty");
}
if (bitmap.depth() != CV_8U && bitmap.depth() != CV_16U)
{
CV_Error(Error::StsUnsupportedFormat, "Input bitmap depth must be CV_8U or CV_16U");
}
if (bitmap.depth() == CV_8U)
{
bitmap.convertTo(bitmap, CV_16U, 257);
}
Mat grayscaleBitmap;
cvtColor(bitmap, grayscaleBitmap, COLOR_BGR2GRAY);
mWidth = bitmap.cols;
mHeight = bitmap.rows;
if (bitsPerPixel <= 0 || bitsPerPixel > 8)
{
CV_Error_(Error::StsBadArg, ("Invalid number of bits per pixel %d. Only values in range [1..8] are accepted.", bitsPerPixel));
}
// Allocate space for pixel data.
int pixelsPerItem = 32 / mBitsPerPixel;
mData.resize((mWidth*mHeight + pixelsPerItem - 1) / pixelsPerItem);
// Convert the bitmap to grayscale and fill the pixel data.
CV_Assert(grayscaleBitmap.depth() == CV_16U);
for (int y = 0; y < mHeight; y++)
{
for (int x = 0; x < mWidth; x++)
{
uint grayVal = ((uint)grayscaleBitmap.at<ushort>((int)y, (int)x)) >> (16 - mBitsPerPixel);
setPixel(x, y, grayVal);
}
}
// Prepare the preallocated contrast matrix for contrast-entropy computations
mCoOccurrenceMatrix.resize((int)(1 << (mBitsPerPixel * 2))); // mCoOccurrenceMatrix size = maxPixelValue^2
}
// HOT PATH 30%
void GrayscaleBitmap::getContrastEntropy(int x, int y, float& contrast, float& entropy, int radius)
{
int fromX = (x > radius) ? x - radius : 0;
int fromY = (y > radius) ? y - radius : 0;
int toX = std::min<int>(mWidth - 1, x + radius + 1);
int toY = std::min<int>(mHeight - 1, y + radius + 1);
for (int j = fromY; j < toY; ++j)
{
for (int i = fromX; i < toX; ++i) // for each pixel in the window
{
updateCoOccurrenceMatrix(getPixel(i, j), getPixel(i, j + 1)); // match every pixel with all 8 its neighbours
updateCoOccurrenceMatrix(getPixel(i, j), getPixel(i + 1, j));
updateCoOccurrenceMatrix(getPixel(i, j), getPixel(i + 1, j + 1));
updateCoOccurrenceMatrix(getPixel(i + 1, j), getPixel(i, j + 1)); // 4 updates per pixel in the window
}
}
contrast = 0.0;
entropy = 0.0;
uint pixelsScale = 1 << mBitsPerPixel;
float normalizer = (float)((toX - fromX) * (toY - fromY) * 4); // four increments per pixel in the window (see above)
for (int j = 0; j < (int)pixelsScale; ++j) // iterate row in a 2D histogram
{
for (int i = 0; i <= j; ++i) // iterate column up to the diagonal in 2D histogram
{
if (mCoOccurrenceMatrix[j*pixelsScale + i] != 0) // consider only non-zero values
{
float value = (float)mCoOccurrenceMatrix[j*pixelsScale + i] / normalizer; // normalize value by number of histogram updates
contrast += (i - j) * (i - j) * value; // compute contrast
entropy -= value * std::log(value); // compute entropy
mCoOccurrenceMatrix[j*pixelsScale + i] = 0; // clear the histogram array for the next computation
}
}
}
}
void GrayscaleBitmap::convertToMat(OutputArray _bitmap, bool normalize) const
{
_bitmap.create((int)getHeight(), (int)getWidth(), CV_8U);
Mat bitmap = _bitmap.getMat();
for (int y = 0; y < getHeight(); ++y)
{
for (int x = 0; x < getWidth(); ++x)
{
uint pixel = getPixel(x, y);
if (normalize && mBitsPerPixel < 8)
{
pixel <<= 8 - mBitsPerPixel;
}
else if (normalize && mBitsPerPixel > 8)
{
pixel >>= mBitsPerPixel - 8;
}
bitmap.at<uchar>((int)y, (int)x) = (uchar)pixel;
}
}
}
}
}
}