ApplyModalityLookupTableCommand Class

Summary

Remaps the image pixels using a LookupTable (LookupTable).

Syntax

Objective-C

C++/CLI

Java

Python

public class ApplyModalityLookupTableCommand : RasterCommand

@interface LTApplyModalityLookupTableCommand : LTRasterCommand

public class ApplyModalityLookupTableCommand 
    extends RasterCommand

public ref class ApplyModalityLookupTableCommand : public RasterCommand

class ApplyModalityLookupTableCommand(RasterCommand):

Remarks

This command is available in the Document and Medical Imaging toolkits.

This class remaps the image pixels through a LookupTable (LookupTable). In the DICOM world, this is referred to as "applying a non-linear Modality LookupTable".
This class is similar to RemapIntensityCommand because it remaps the image pixel values through a LookupTable. The class differs from RemapIntensityCommand as follows: ApplyModalityLookupTableCommand allows you to specify an incomplete LookupTable. Values less than the first mapped index will be mapped to the first entry in the palette. Values higher than "first mapped index" + "LookupTable length" will be mapped to the last entry in the LookupTable. ApplyModalityLookupTableCommand only works on grayscale images. ApplyModalityLookupTableCommand can create signed images. The output image will be signed (if ModalityLookupTableCommandFlags.SignedLookupTable is set), or unsigned (ModalityLookupTableCommandFlags.SignedLookupTable is not set).
The values in the LookupTable will be masked such that only the useful bits in the image are considered. The values are considered as if the image pixel values are normalized, LowBit = 0.
For example, let's say the image is: BitsPerPixel = 12 LowBit = 4 HighBit = 10 In this case, there are 10-4+1=7 valid bits. This means that there are 128 values to remap. For every pixel, ApplyModalityLookupTableCommand will do the following:
Take the pixel value, shift it to the right by 4 and mask out the high bits, producing a value (val = 0..127).
The value is remapped according to the LookupTable (values smaller than FirstStoredPixelValueMapped (property of DicomLookupTableDescriptor class) are mapped to first LookupTable entry, while values greater than FirstStoredPixelValueMapped (property of DicomLookupTableDescriptor class) + LookupTable->Length are mapped to the last LookupTable entry).
After remapping, the value is shifted to the left by 4 and will replace bits 4 thru 10 from the original image.
If the image is signed, the indices for the LookupTable are assumed to be signed and be between -32768 and +32767.
If the image is unsigned, the indices are unsigned and are between 0..65535.
It is recommended to always set the ModalityLookupTableCommandFlags.UpdateMinMax flag.
This class is helpful in applying what is referred to as a "Non-Linear Modality LookupTable" in the DICOM world. According to the DICOM standard a "Modality LookupTable" defines the transformation of manufacturer-dependent pixel values into pixel values, which are manufacturer independent (e.g. Hounsfield units for CT, Optical Density for film digitizers, etc.).
This class supports 12 and 16-bit grayscale. Support for 12 and 16-bit grayscale is available only in the Document/Medical toolkits.
This command does not support 32-bit grayscale images.

For more information, refer to Changing Brightness and Contrast.

Example

Run the ApplyModalityLookupTableCommand on an image.

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing.Core; 
 
public void ApplyModalityLookupTableCommandExample() 
{ 
   // Load an image 
   RasterCodecs codecs = new RasterCodecs(); 
   codecs.ThrowExceptionsOnInvalidImages = true; 
 
   RasterImage image = codecs.Load(Path.Combine(LEAD_VARS.ImagesDir, "IMAGE2.dcm")); 
 
   // Prepare the command 
   int i; 
   short[] pLookupTable = new short[0x10000]; 
   DicomLookupTableDescriptor LookupTableDescriptor = new DicomLookupTableDescriptor(); 
 
   // set a LookupTable which reduces the intensity of each pixel to half 
   for (i = 0; i <= 0xFFFF; i++) 
      pLookupTable[i] = (short)(i / 2); 
 
   // fill the LookupTableDescriptor object 
   LookupTableDescriptor.FirstStoredPixelValueMapped = 0; 
   LookupTableDescriptor.EntryBits = 16; 
 
   // apply the LookupTable 
   ApplyModalityLookupTableCommand command = new ApplyModalityLookupTableCommand(); 
   command.Flags = ModalityLookupTableCommandFlags.None; 
   command.LookupTable = pLookupTable; 
   command.LookupTableDescriptor = LookupTableDescriptor; 
   command.Run(image); 
 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 
}