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lightmap.go
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/
lightmap.go
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package colors
type LightMap []Luminance
// Hex returns all luminance value as a hex encoded string.
func (m LightMap) Hex() (result string) {
for _, luminance := range m {
if luminance > 15 {
result += "F"
} else {
result += luminance.Hex()
}
}
return result
}
type diffValue struct {
a []int
b []int
}
// Pixel comparisons for calculating the diff value.
var diffValues = []diffValue{
{a: []int{4, 4, 4, 4}, b: []int{1, 3, 5, 7}},
{a: []int{0}, b: []int{1}},
{a: []int{0}, b: []int{3}},
{a: []int{2}, b: []int{1}},
{a: []int{2}, b: []int{5}},
{a: []int{6}, b: []int{3}},
{a: []int{6}, b: []int{7}},
{a: []int{8}, b: []int{5}},
{a: []int{8}, b: []int{7}},
}
/*
Alternative values to experiment with:
{a: []int{4, 4, 4, 4}, b: []int{1, 3, 5, 7}},
{a: []int{0}, b: []int{2}},
{a: []int{8}, b: []int{6}},
{a: []int{0}, b: []int{1}},
{a: []int{1}, b: []int{2}},
{a: []int{2}, b: []int{5}},
{a: []int{8}, b: []int{7}},
{a: []int{7}, b: []int{6}},
{a: []int{5}, b: []int{8}},
{a: []int{6}, b: []int{3}},
Other ideas:
- Use Lightness instead of luminance
- Use more pixels (difficult as we only have 3x3 thumbs right now)
- Iterative calculation using smaller offsets for each round (current offset is +4)
For a more complex implementation, see
https://github.com/EdjoLabs/image-match/blob/master/image_match/goldberg.py
http://www.cs.cmu.edu/~hcwong/Pdfs/icip02.ps
General blog post on Perceptual image hashing:
https://jenssegers.com/perceptual-image-hashes
*/
// Diff returns an integer that can be used to find similar images.
func (m LightMap) Diff() (result int) {
if len(m) != 9 {
return 0
}
result = 1
for _, val := range diffValues {
result = result << 1
a := 0
b := 0
for _, i := range val.a {
a += int(m[i])
}
for _, i := range val.b {
b += int(m[i])
}
if a+4 > b {
result += 1
}
}
return result
}