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>
---
internal/rendertest/util_test.go | 48 +++++++++++++++++++++++++++-----
1 file changed, 41 insertions(+), 7 deletions(-)
diff --git a/internal/rendertest/util_test.go b/internal/rendertest/util_test.go
index 6a3a164..daa31a8 100644
--- a/internal/rendertest/util_test.go
+++ b/internal/rendertest/util_test.go
@@ -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) {
--
2.30.0