fix: Correct float access to lut array (#302) (#303)

* Correct float access to lut array (#302)

* Fix performance issue (#302)

Co-authored-by: pleduff <[email protected]>

Author: pierreldff

src/internal/generateLut.js

@@ -28,8 +28,9 @@ export default function (image, windowWidth, windowCenter, invert, modalityLUT,
   }
 
   const lut = image.cachedLut.lutArray;
+  var slopeOrInterceptAreFloat = !!(image.slope % 1) || !!(image.intercept % 1);
   const mlutfn = getModalityLUT(image.slope, image.intercept, modalityLUT);
-  const vlutfn = getVOILUT(windowWidth, windowCenter, voiLUT);
+  const vlutfn = getVOILUT(windowWidth, windowCenter, voiLUT, slopeOrInterceptAreFloat);
 
   if (invert === true) {
     for (let storedValue = minPixelValue; storedValue <= maxPixelValue; storedValue++) {

src/internal/getVOILut.js

@@ -30,12 +30,14 @@ function generateLinearVOILUT (windowWidth, windowCenter) {
 /**
  * Generate a non-linear volume of interest lookup table
  *
- * @param {LUT} voiLUT Volume of Interest Lookup Table Object
+ * @param {LUT} voiLUT Volume of Interest Lookup Table Object 
+ * @param {Boolean} roundModalityLUTValues Do a Math.round of modality lut to compute non linear voilut
+ 
  *
  * @returns {VOILUTFunction} VOI LUT mapping function
  * @memberof VOILUT
  */
-function generateNonLinearVOILUT (voiLUT) {
+function generateNonLinearVOILUT (voiLUT, roundModalityLUTValues) {
   // We don't trust the voiLUT.numBitsPerEntry, mainly thanks to Agfa!
   const bitsPerEntry = Math.max(...voiLUT.lut).toString(2).length;
   const shift = bitsPerEntry - 8;
@@ -49,8 +51,10 @@ function generateNonLinearVOILUT (voiLUT) {
     } else if (modalityLutValue >= maxValueMapped) {
       return maxValue;
     }
-
-    return voiLUT.lut[modalityLutValue - voiLUT.firstValueMapped] >> shift;
+	if( roundModalityLUTValues )
+		return voiLUT.lut[Math.round(modalityLutValue) - voiLUT.firstValueMapped] >> shift;
+	else
+		return voiLUT.lut[modalityLutValue - voiLUT.firstValueMapped] >> shift;
   };
 }
 
@@ -61,13 +65,14 @@ function generateNonLinearVOILUT (voiLUT) {
  * @param {Number} windowWidth Window Width
  * @param {Number} windowCenter Window Center
  * @param {LUT} [voiLUT] Volume of Interest Lookup Table Object
+ * @param {Boolean} roundModalityLUTValues Do a Math.round of modality lut to compute non linear voilut
  *
  * @return {VOILUTFunction} VOI LUT mapping function
  * @memberof VOILUT
  */
-export default function (windowWidth, windowCenter, voiLUT) {
+export default function (windowWidth, windowCenter, voiLUT, roundModalityLUTValues) {
   if (voiLUT) {
-    return generateNonLinearVOILUT(voiLUT);
+    return generateNonLinearVOILUT(voiLUT, roundModalityLUTValues);
   }
 
   return generateLinearVOILUT(windowWidth, windowCenter);