Code in fo-dicom to apply window width and center on an image #1903

soothingmusic · 2024-03-20T08:34:38Z

soothingmusic
Mar 20, 2024

I am using fo-dicom to render images and change the window width and center of the images. All works great.

I have a scenario where i dont have the dicom file and yet, and i need to apply the window width and center.
I have looked at the fo-dicom code and I see that we have Modality LUT class that overrides indexer that transforms the pixel value by applying rescale slope and intercept..

This is then used while rendering the image.

public void Render(ILUT lut, int[] output)
       {
           var data = Data;
           if (lut == null)
           {
               //.........
           }
           else
           {
               Parallel.For(0, Height, y =>
               {
                   for (int i = Width * y, e = i + Width; i < e; i++)
                   {
                       output[i] = (int)lut[data[i]];
                   }
               }
               );
           }
       }

I would like to know where exactly the window width and center are applied?

I would have expected following code somewhere to apply ww/wl..

public byte[] AdjustWindowWidthAndLevel(byte[] image, int width, int height, ushort newWindowWidth, ushort newWindowLevel, ushort maxPixelValue)
 {
     byte[] adjustedImage = new byte[image.Length];

     // Calculate the scaling factor for adjusting pixel values
     double scalingFactor = (double)newWindowWidth / (double)maxPixelValue;

     // Adjust the pixel values based on the new window width and level
     for (int i = 0; i < image.Length; i += 2)
     {
         ushort pixelValue = BitConverter.ToUInt16(image, i);

         // Apply window level adjustment
         int adjustedPixelValue = pixelValue - newWindowLevel;

         // Apply window width adjustment
         adjustedPixelValue = (int)Math.Round(adjustedPixelValue * scalingFactor);

         // Clamp the adjusted pixel value within the valid range
         adjustedPixelValue = Math.Max(0, Math.Min(adjustedPixelValue, maxPixelValue));

         byte[] adjustedPixelBytes = BitConverter.GetBytes((ushort)adjustedPixelValue);
         adjustedImage[i] = adjustedPixelBytes[0];
         adjustedImage[i + 1] = adjustedPixelBytes[1];
     }

     return adjustedImage;
 }

Where can i find this in fo-dicom code??

gofal · 2024-03-24T19:29:09Z

gofal
Mar 24, 2024
Maintainer

fo-dicom uses a more generic approach than your code. The calculation of the pixel data depending on WindowLevel and WindowWith does not apply to the definition in DICOM-Standard. WindowWidth and WindowCenter are not always applied in a linear way, sometimes you have to use SIGMOID, a exponential function. This depends on the content of VOILUTFunction (https://dicom.innolitics.com/ciods/breast-projection-x-ray-image/breast-projection-x-ray-image-multi-frame-functional-groups/52009229/00289132/00281056)

Then there are other properties like rescale slope and rescale intercept.

Futhermore some images contain Lookup-Tables, that have to be applied.

Your code assumes that the pixeldata always has 16 bits, but it also may be 8 bit, or 24 bit color.

etc etc etc

In fo-dicom the ILUT interface is the base class for all of these transformations, and the IPipeline is the base interface for the various factory implementations: GenericGrayscale, PaletteColor and RGBColor.
Each of these pipelines reads all the various dicomtags and builds up the renderpipeline by applying a chain of ILUT-Transformations. (https://dicom.nema.org/medical/dicom/current/output/chtml/part04/sect_n.2.html)

The DicomImage class handles this all for you. You have to create an instance of DicomImage. If you call .RenderImage() then all those pipelines are built up and the image is rendered correctly. You can adjust the rendering by changing the properties WindowCenter, WindowWidth, UseVOILUT, ShowOverlays etc.

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jaime-olivares · 2024-12-06T01:08:49Z

jaime-olivares
Dec 6, 2024

The question has been solved with no further feedback. This issue may be closed.

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Code in fo-dicom to apply window width and center on an image #1903

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soothingmusic Mar 20, 2024

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gofal Mar 24, 2024 Maintainer

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jaime-olivares Dec 6, 2024

soothingmusic
Mar 20, 2024

gofal
Mar 24, 2024
Maintainer

jaime-olivares
Dec 6, 2024