To integrate your tool in an other projects, the module path must be changed from imgdiff to github.com/n7olkachev/imgdiff.

So one can use your project as package. It would be great, e.g. in unit tests.

Version: 1.0.0

It computed the number of different pixels, but the output is empty.

Example:

curl -O https://user-images.githubusercontent.com/640840/112396875-03837d80-8ccf-11eb-8aa2-ef605eb6ab60.png
curl -O https://user-images.githubusercontent.com/640840/112396905-0da57c00-8ccf-11eb-8cd3-dab6d42cbfa1.png

./bin/imgdiff-darwin-amd64 --threshold 0.01 112396875-03837d80-8ccf-11eb-8aa2-ef605eb6ab60.png 112396905-0da57c00-8ccf-11eb-8cd3-dab6d42cbfa1.png output_diff.png

I get this output:

Failure! Images are different.
Different pixels: 3992

But the file is empty:

0B 24 Mar 18:34 output_diff.png

Any ideas? This is a fantastic tool that really boosted our end-to-end screenshots tests. I get these zero-byte files every ~1-2 in 100 diffs.

First of all, I want to say thank you for doing this. I spent pretty a lot of time on making it works, but thanks to this library I realized that one of the dependencies were doing massive data copying and finally made it the fastest :D

If you will manually run odiff v2 with the same cypress.io screenshot you will see that

| Command | Mean [s] | Min [s] | Max [s] | Relative | |:---|---:|---:|---:|---:| | odiff www.cypress.io.png www.cypress.io-1.png www.cypress-diff.png | 1.194 ± 0.017 | 1.173 | 1.217 | 1.04 ± 0.06 | | ./main www.cypress.io.png www.cypress.io-1.png www.cypress-diff.png | 1.146 ± 0.068 | 1.096 | 1.321 | 1.00 |

wow, its slower. But a little big magic of removing parallelization

diff --git a/pkg/imgdiff/imgdiff.go b/pkg/imgdiff/imgdiff.go
index 3af22c0..8a7ae41 100644
--- a/pkg/imgdiff/imgdiff.go
+++ b/pkg/imgdiff/imgdiff.go
@@ -4,8 +4,6 @@ import (
 	"image"
 	"image/color"
 	"imgdiff/pkg/yiq"
-	"runtime"
-	"sync"
 	"sync/atomic"
 )
 
@@ -30,43 +28,29 @@ func Diff(image1 image.Image, image2 image.Image, options *Options) *Result {
 
 	diff := image.NewNRGBA(image1.Bounds())
 
-	wg := sync.WaitGroup{}
+	diffPixelsCounter := 0
 
-	cpus := runtime.NumCPU()
+	for y := 0; y <= image1.Bounds().Max.Y; y++ {
+		for x := 0; x <= image1.Bounds().Max.X; x++ {
+			pixel1, pixel2 := image1.At(x, y), image2.At(x, y)
 
-	for i := 0; i < cpus; i++ {
-		wg.Add(1)
+			if pixel1 != pixel2 {
+				delta := yiq.Delta(pixel1, pixel2)
 
-		go func(i int) {
-			diffPixelsCounter := 0
+				if delta > maxDelta {
+					diff.SetNRGBA(x, y, color.NRGBA{R: 255, G: 0, B: 0, A: 255})
 
-			for y := i; y <= image1.Bounds().Max.Y; y += cpus {
-				for x := 0; x <= image1.Bounds().Max.X; x++ {
-					pixel1, pixel2 := image1.At(x, y), image2.At(x, y)
-
-					if pixel1 != pixel2 {
-						delta := yiq.Delta(pixel1, pixel2)
-
-						if delta > maxDelta {
-							diff.SetNRGBA(x, y, color.NRGBA{R: 255, G: 0, B: 0, A: 255})
-
-							diffPixelsCounter++
-						}
-					} else if options.DiffImage {
-						diff.Set(x, y, pixel1)
-					}
+					diffPixelsCounter++
 				}
+			} else if options.DiffImage {
+				diff.Set(x, y, pixel1)
 			}
-
-			if diffPixelsCounter > 0 {
-				atomic.AddUint64(&diffPixelsCount, uint64(diffPixelsCounter))
-			}
-
-			wg.Done()
-		}(i)
+		}
 	}
 
-	wg.Wait()
+	if diffPixelsCounter > 0 {
+		atomic.AddUint64(&diffPixelsCount, uint64(diffPixelsCounter))
+	}
 
 	return &Result{
 		Equal:           diffPixelsCount == 0,

And odiff becomes 2x faster

| Command | Mean [s] | Min [s] | Max [s] | Relative | |:---|---:|---:|---:|---:| | odiff www.cypress.io.png www.cypress.io-1.png www.cypress-diff.png | 1.192 ± 0.018 | 1.172 | 1.229 | 1.00 | | ./main www.cypress.io.png www.cypress.io-1.png www.cypress-diff.png | 2.616 ± 0.023 | 2.587 | 2.649 | 2.19 ± 0.04 |

Actually, it's not a problem of making such kinds of tools multi-core, but it doesn't make a lot of sense, cause they are mostly will be executed as a child process. But parallelizing itself costs, so if we will take a little bit smaller image – even with parallelization it is slower

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative | |:---|---:|---:|---:|---:| | odiff donkey.png donkey-2.png donkey-diff.png | 370.9 ± 35.8 | 347.7 | 438.5 | 1.00 | | ./main donkey.png donkey-2.png donkey-diff.png | 381.6 ± 7.6 | 375.2 | 399.6 | 1.03 ± 0.10 |

It's your turn :D

https://github.com/n7olkachev/imgdiff/blob/3eef05cf1006158db2aab884cb3ca755dd180090/pkg/imgdiff/imgdiff.go#L30

I'm confused why this line is like this. I'd assume the threshold (from 0 to 1) only needs to be multiplied once?

Just saw this on Hacker News and I was wondering if you would like to add a license to the imgdiff tool since, by default, copyright is "all rights reserved". A list of popular licenses are available here, though I might suggest the MIT license.

sir instead of store output image to local drive ,how can i get the four corner point x y value array top x,y lowest x,y so i can crop the area from original file