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Add entropy calculation to images.

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This commit is contained in:
Pavel Krajcevski 2013-10-18 04:12:32 -04:00
parent 54f5030aeb
commit f597ec2f77
2 changed files with 59 additions and 0 deletions
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3
Base/include/Image.h
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@ -107,6 +107,9 @@ namespace FasTC {
double ComputePSNR(Image<PixelType> *other);
double ComputeSSIM(Image<PixelType> *other);
double ComputeEntropy();
double ComputeMeanLocalEntropy();
// Function to allow derived classes to populate the pixel array.
// This may involve decompressing a compressed image or otherwise

56
Base/src/Image.cpp
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@ -406,6 +406,62 @@ double Image<PixelType>::ComputeSSIM(Image<PixelType> *other) {
return mssim / static_cast<double>(w * h);
}
template<typename PixelType>
double Image<PixelType>::ComputeMeanLocalEntropy() {
const uint32 kKernelSz = 15;
const uint32 kHalfKernelSz = kKernelSz / 2;
Image<IPixel> entropyIdx(GetWidth() - kKernelSz + 1, GetHeight() - kKernelSz + 1);
for(uint32 j = kHalfKernelSz; j < GetHeight() - kHalfKernelSz; j++) {
for(uint32 i = kHalfKernelSz; i < GetWidth() - kHalfKernelSz; i++) {
Image<PixelType> subImg(kKernelSz, kKernelSz);
for(uint32 y = 0; y < kKernelSz; y++)
for(uint32 x = 0; x < kKernelSz; x++) {
subImg(x, y) = (*this)(i - kHalfKernelSz + x, j - kHalfKernelSz + y);
}
entropyIdx(i-kHalfKernelSz, j-kHalfKernelSz) =
static_cast<float>(subImg.ComputeEntropy());
}
}
double sum = 0;
for(uint32 j = 0; j < entropyIdx.GetHeight(); j++)
for(uint32 i = 0; i < entropyIdx.GetWidth(); i++) {
sum += static_cast<float>(entropyIdx(i, j));
}
return sum / (entropyIdx.GetHeight() * entropyIdx.GetWidth());
}
template<typename PixelType>
double Image<PixelType>::ComputeEntropy() {
uint32 hist[256];
memset(hist, 0, sizeof(hist));
ComputePixels();
Image<IPixel> intensity(GetWidth(), GetHeight());
ConvertTo(intensity);
for(uint32 j = 0; j < GetHeight(); j++) {
for(uint32 i = 0; i < GetWidth(); i++) {
float iflt = static_cast<float>(intensity(i, j));
uint32 iv = static_cast<uint32>(iflt * 255.0f + 0.5f);
assert(iv < 256);
hist[iv]++;
}
}
double ret = 0;
for(uint32 i = 0; i < 256; i++) {
if(hist[i] > 0) {
float p = static_cast<float>(hist[i]) / static_cast<float>(GetHeight() * GetWidth());
ret += p * log2(p);
}
}
return -ret;
}
// !FIXME! These won't work for non-RGBA8 data.
template<typename PixelType>
void Image<PixelType>::ConvertToBlockStreamOrder() {