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internal/rendertest: use a YIQ-based algorithm to compare images

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This PR implements an image comparison algorithm in the NTSC YIQ color
space, as described in:

  Measuring perceived color difference using YIQ NTSC
  transmission color space in mobile applications.
  Yuriy Kotsarenko, Fernando Ramos.

An electronic version is available at:

- http://www.progmat.uaem.mx:8080/artVol2Num2/Articulo3Vol2Num2.pdf

This should allow the image comparison to be a tad more robust than
comparing plain uint8 pixel values.

Signed-off-by: Sebastien Binet <s@sbinet.org>
This commit is contained in:
Sebastien Binet
2021-01-01 16:15:29 +00:00
committed by Elias Naur
parent 79016bcc4a
commit 8676a73a91
1 changed files with 41 additions and 7 deletions
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internal/rendertest/util_test.go
+41 -7
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@@ -1,3 +1,5 @@
// SPDX-License-Identifier: Unlicense OR MIT
package rendertest
import (
@@ -180,15 +182,47 @@ func verifyRef(t *testing.T, img *image.RGBA, frame int) (ok bool) {
}
func colorsClose(c1, c2 color.RGBA) bool {
return close(c1.A, c2.A) && close(c1.R, c2.R) && close(c1.G, c2.G) && close(c1.B, c2.B)
const delta = 0.01 // magic value obtained from experimentation.
return yiqEqApprox(c1, c2, delta)
}
func close(b1, b2 uint8) bool {
if b1 > b2 {
b1, b2 = b2, b1
}
diff := b2 - b1
return diff < 16
// yiqEqApprox compares the colors of 2 pixels, in the NTSC YIQ color space,
// as described in:
//
// Measuring perceived color difference using YIQ NTSC
// transmission color space in mobile applications.
// Yuriy Kotsarenko, Fernando Ramos.
//
// An electronic version is available at:
//
// - http://www.progmat.uaem.mx:8080/artVol2Num2/Articulo3Vol2Num2.pdf
func yiqEqApprox(c1, c2 color.RGBA, d2 float64) bool {
const max = 35215.0 // difference between 2 maximally different pixels.
var (
r1 = float64(c1.R)
g1 = float64(c1.G)
b1 = float64(c1.B)
r2 = float64(c2.R)
g2 = float64(c2.G)
b2 = float64(c2.B)
y1 = r1*0.29889531 + g1*0.58662247 + b1*0.11448223
i1 = r1*0.59597799 - g1*0.27417610 - b1*0.32180189
q1 = r1*0.21147017 - g1*0.52261711 + b1*0.31114694
y2 = r2*0.29889531 + g2*0.58662247 + b2*0.11448223
i2 = r2*0.59597799 - g2*0.27417610 - b2*0.32180189
q2 = r2*0.21147017 - g2*0.52261711 + b2*0.31114694
y = y1 - y2
i = i1 - i2
q = q1 - q2
diff = 0.5053*y*y + 0.299*i*i + 0.1957*q*q
)
return diff <= max*d2
}
func (r result) expect(x, y int, col color.RGBA) {