fix(vtkimagedata.computehistogram): incorrect value of variance/sigma

jadh4v · jadh4v · commit ed07178af39b · 2021-11-11T13:51:13.000-05:00
Corrected the equation for variance which also leads to correct
value of standard deviation (sigma).
diff --git a/Sources/Common/DataModel/ImageData/index.js b/Sources/Common/DataModel/ImageData/index.js
@@ -410,7 +410,9 @@ function vtkImageData(publicAPI, model) {
     }
 
     const average = inum > 0 ? isum / inum : 0;
-    const variance = sumOfSquares - average * average;
+    const variance = inum
+      ? Math.abs(sumOfSquares / inum - average * average)
+      : 0;
     const sigma = Math.sqrt(variance);
 
     return {

Original file line number	Diff line number	Diff line change
`@@ -410,7 +410,9 @@ function vtkImageData(publicAPI, model) {`
`410`	`410`	`}`
`411`	`411`
`412`	`412`	`const average = inum > 0 ? isum / inum : 0;`
`413`		`- const variance = sumOfSquares - average * average;`
	`413`	`+ const variance = inum`
	`414`	`+ ? Math.abs(sumOfSquares / inum - average * average)`
	`415`	`+ : 0;`
`414`	`416`	`const sigma = Math.sqrt(variance);`
`415`	`417`
`416`	`418`	`return {`