92 lines
2.5 KiB
Go
92 lines
2.5 KiB
Go
package images4
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// Similar returns similarity verdict based on Euclidean
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// and proportion similarity.
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func Similar(iconA, iconB IconT) bool {
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if !propSimilar(iconA, iconB) {
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return false
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}
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if !eucSimilar(iconA, iconB) {
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return false
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}
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return true
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}
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// propSimilar gives a similarity verdict for image A and B based on
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// their height and width. When proportions are similar, it returns
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// true.
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func propSimilar(iconA, iconB IconT) bool {
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return PropMetric(iconA, iconB) < thProp
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}
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// PropMetric gives image proportion similarity metric for image A
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// and B. The smaller the metric the more similar are images by their
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// x-y size.
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func PropMetric(iconA, iconB IconT) (m float64) {
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// Filtering is based on rescaling a narrower side of images to 1,
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// then cutting off at threshold of a longer image vs shorter image.
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xA, yA := float64(iconA.ImgSize.X), float64(iconA.ImgSize.Y)
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xB, yB := float64(iconB.ImgSize.X), float64(iconB.ImgSize.Y)
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if xA <= yA { // x to 1.
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yA = yA / xA
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yB = yB / xB
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if yA > yB {
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m = (yA - yB) / yA
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} else {
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m = (yB - yA) / yB
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}
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} else { // y to 1.
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xA = xA / yA
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xB = xB / yB
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if xA > xB {
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m = (xA - xB) / xA
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} else {
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m = (xB - xA) / xB
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}
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}
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return m
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}
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// eucSimilar gives a similarity verdict for image A and B based
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// on Euclidean distance between pixel values of their icons.
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// When the distance is small, the function returns true.
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// iconA and iconB are generated with the Icon function.
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// eucSimilar wraps EucMetric with well-tested thresholds.
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func eucSimilar(iconA, iconB IconT) bool {
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m1, m2, m3 := EucMetric(iconA, iconB)
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return m1 < thY && // Luma as most sensitive.
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m2 < thCbCr &&
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m3 < thCbCr
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}
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// EucMetric returns Euclidean distances between 2 icons.
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// These are 3 metrics corresponding to each color channel.
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// Distances are squared, not to waste CPU on square root calculations.
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// Note: color channels of icons are YCbCr (not RGB).
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func EucMetric(iconA, iconB IconT) (m1, m2, m3 float64) {
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var cA, cB uint16
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for i := 0; i < numPix; i++ {
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// Channel 1.
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cA = iconA.Pixels[i]
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cB = iconB.Pixels[i]
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m1 += ((float64(cA) - float64(cB)) * one255th2 * (float64(cA) - float64(cB)))
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// Channel 2.
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cA = iconA.Pixels[i+numPix]
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cB = iconB.Pixels[i+numPix]
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m2 += ((float64(cA) - float64(cB)) * one255th2 * (float64(cA) - float64(cB)))
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// Channel 3.
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cA = iconA.Pixels[i+2*numPix]
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cB = iconB.Pixels[i+2*numPix]
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m3 += ((float64(cA) - float64(cB)) * one255th2 * (float64(cA) - float64(cB)))
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}
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return m1, m2, m3
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}
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