Floating point lookup table support

[tostein]

Description: I was wondering if there is any support for floating point based image data (like a DICOM parametric map) to use a colormap.

Problem: Usage of colormaps within a image stack for floating point based image data leads to errors within storedPixelDataToCanvasImageDataColorLUT.js because index based array access requires integer values.

Proposal: If there is no solution yet, one could find for a given floating point value the closest integers from existing lookup-tables and do a linear interpolation between the two colors.

Something like the following would fit into the named ImageDataColorLUT.js:

      let value pixelData[storedPixelDataIndex++];
      let cLeft = clut[Math.floor(value)];
      let cRight = clut[Math.ceil(value)];
      canvasImageDataData[canvasImageDataIndex++] = parseInt((cleft[0] + cRight[0])/2.0);
      canvasImageDataData[canvasImageDataIndex++] = parseInt((cleft[1] + cRight[1])/2.0);
      canvasImageDataData[canvasImageDataIndex++] = parseInt((cleft[2] + cRight[2])/2.0);
      canvasImageDataData[canvasImageDataIndex++] = parseInt((cleft[3] + cRight[3])/2.0);

It must be checked that typeof pixel.Data == Float32Array

For now i am rounding my values to integers and use the lookup tables. But that should be better shouldn't it?

@pieper

[swederik]

Hi Tobias,

How are you loading this image? With the WADO Image Loader we convert any float pixel data to integers and use that for rendering when the image is loaded:

https://github.com/cornerstonejs/cornerstoneWADOImageLoader/blob/da4c03933b4b6f634c59614a6aa1a479980f2968/src/imageLoader/createImage.js#L18

The float pixel data remains, and is kept in the floatPixelData property: https://github.com/cornerstonejs/cornerstoneWADOImageLoader/blob/da4c03933b4b6f634c59614a6aa1a479980f2968/src/imageLoader/createImage.js#L132

So I am a bit surprised that the issues you mention above exist, unless you are using a custom image loader. In that case, it's probably easiest to do the same as what we are doing in the WADO Image Loader.

[tostein]

Thanks for your fast answer. Yes i am using a custom loader. I will considering using the WADO image loader instead.

[pieper]

@NussknackerXXL you could also just add the rescaling code to your custom loader.