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/**
* Volume of Interest Lookup Table Function
*
* @typedef {Function} VOILUTFunction
*
* @param {Number} modalityLutValue
* @returns {Number} transformed value
* @memberof Objects
*/
/**
* @module: VOILUT
*/
/**
* Generates the linear VOI LUT function.
* From the DICOM standard:
* https://dicom.nema.org/medical/dicom/current/output/html/part03.html#sect_C.11.2.1.2.1
* ((x - (c - 0.5)) / (w-1) + 0.5) * (ymax- ymin) + ymin
* clipped to the ymin...ymax range
*
* @param {Number} windowWidth Window Width
* @param {Number} windowCenter Window Center
* @returns {VOILUTFunction} VOI LUT mapping function
* @memberof VOILUT
*/
function generateLinearVOILUT(windowWidth: number, windowCenter: number) {
return function (modalityLutValue) {
const value =
((modalityLutValue - (windowCenter - 0.5)) / (windowWidth - 1) + 0.5) *
255.0;
return Math.min(Math.max(value, 0), 255);
};
}
/**
* Generate a non-linear volume of interest lookup table
*
* @param {LUT} voiLUT Volume of Interest Lookup Table Object
*
* @returns {VOILUTFunction} VOI LUT mapping function
* @memberof VOILUT
*/
function generateNonLinearVOILUT(voiLUT) {
// We don't trust the voiLUT.numBitsPerEntry, mainly thanks to Agfa!
const bitsPerEntry = Math.max(...voiLUT.lut).toString(2).length;
const shift = bitsPerEntry - 8;
const minValue = voiLUT.lut[0] >> shift;
const maxValue = voiLUT.lut[voiLUT.lut.length - 1] >> shift;
const maxValueMapped = voiLUT.firstValueMapped + voiLUT.lut.length - 1;
return function (modalityLutValue) {
if (modalityLutValue < voiLUT.firstValueMapped) {
return minValue;
} else if (modalityLutValue >= maxValueMapped) {
return maxValue;
}
return voiLUT.lut[modalityLutValue - voiLUT.firstValueMapped] >> shift;
};
}
/**
* Retrieve a VOI LUT mapping function given the current windowing settings
* and the VOI LUT for the image
*
* @param {Number} windowWidth Window Width
* @param {Number} windowCenter Window Center
* @param {LUT} [voiLUT] Volume of Interest Lookup Table Object
*
* @return {VOILUTFunction} VOI LUT mapping function
* @memberof VOILUT
*/
export default function (windowWidth: number, windowCenter: number, voiLUT) {
Iif (voiLUT) {
return generateNonLinearVOILUT(voiLUT);
}
return generateLinearVOILUT(windowWidth, windowCenter);
}
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