/**
* Computes the standard deviations of the intensities of all blocks and
* the minimum standard deviation
*/
func computeStdevs(blocks []image.Image) (float64, []float64) {
stdevs := make([]float64, len(blocks), len(blocks))
minStdev := math.Inf(1)
ch := make(chan indexValuePair)
for i, block := range blocks {
go func(i int, block image.Image) {
variance, mean := 0.0, 0.0
minX, minY := block.Bounds().Min.X, block.Bounds().Min.Y
maxX, maxY := block.Bounds().Max.X, block.Bounds().Max.Y
total := float64((maxX - minX) * (maxY - minY))
for i := minX; i < maxX; i++ {
for j := minY; j < maxY; j++ {
mean += utils.Intensity(block.At(i, j))
}
}
mean /= total
for i := minX; i < maxX; i++ {
for j := minY; j < maxY; j++ {
variance += math.Pow(utils.Intensity(block.At(i, j))-mean, 2)
}
}
ch <- indexValuePair{i: i, value: math.Sqrt(variance / total)}
}(i, block)
}
for i := 0; i < len(blocks); i++ {
pair := <-ch
stdevs[pair.i] = pair.value
minStdev = utils.MinF(pair.value, minStdev)
}
close(ch)
return minStdev, stdevs
}
/**
* Returns the differences between the intensities between each original block and
* the filtered one. Also return the mean of those differences.
*/
func diffsAndMeanDiff(origBlocks, filtBlocks []image.Image) ([]float64, float64) {
total := float64(len(origBlocks) * BLOCK_WIDTH * BLOCK_HEIGHT)
diffs := make([]float64, int(total), int(total))
mean := 0.0
for b := 0; b < len(origBlocks); b++ {
minX, minY := origBlocks[b].Bounds().Min.X, origBlocks[b].Bounds().Min.Y
maxX, maxY := origBlocks[b].Bounds().Max.X, origBlocks[b].Bounds().Max.Y
for i := minX; i < maxX; i++ {
for j := minY; j < maxY; j++ {
intensityFiltered := utils.Intensity(filtBlocks[b].At(i-minX, j-minY))
intensityOriginal := utils.Intensity(origBlocks[b].At(i, j))
diffs[b] = math.Abs(intensityFiltered - intensityOriginal)
mean += diffs[b] / total
}
}
}
return diffs, mean
}
/**
* Computes the absolute difference between the two pixels intensities.
*/
func IntensityDifference(p1 graph.Pixel, p2 graph.Pixel) float64 {
return math.Abs(utils.Intensity(p2.Color) - utils.Intensity(p1.Color))
}