X4D XRay/DRR Settings

From Visual3D Wiki Documentation
Jump to: navigation, search

Once the DRR images have been generated for a particular set of bone poses, the DRR images and the X-ray images are processed using the same method, then compared to each other. The processing consists of the following steps:

  1. perform a Sobel edge detection on the image
  2. threshold the edge-detection image
  3. multiply the edge-detection image by a weighting factor and add it to the original image
  4. threshold the merged image
  5. scale the result

The following X-ray and DRR parameters are used during processing:

X-ray
Edge/Intensity Merge
This is the value of the weighting factor in step 3.
Edge Capping (%)
These two values values govern the edge thresholding in step 2. Pixels in the edge image whose values are greater than the edge capping maximum are set to zero.
Very bright pixels (sharp edges) are usually inorganic objects like EMG electrodes or metal plates or wires. They can be removed from the edge image by lowering the edge capping maximum from 100. Every pixel in the edge image whose value is above the edge capping minimum is set to the edge capping minimum. This effectively strengthens weaker edges (those below the edge capping minimum) because the entire image is scaled later.
Image Thresholds (%)
These two values values govern the thresholding in step 4. All pixels above the image threshold maximum are set to the maximum, and all pixels below the image threshold minimum are set to 0. Much of the time these thresholds should be left at 100 and 0. However, there are times when it is useful to raise the minimum above zero to mask soft tissue regions, and lower the maximum from 100 to remove artificial edges, such as the end of a CT bone that is within the X-ray image.
Image Scale
This is the scale factor used in step 5.
DRR
Edge/Intensity Merge
This is the value of the weighting factor in step 3.
Edge Capping (%)
These two values values govern the edge thresholding in step 2. Pixels in the edge image whose values are greater than the edge capping maximum are set to zero.
Very bright pixels (sharp edges) are usually inorganic objects like EMG electrodes or metal plates or wires. They can be removed from the edge image by lowering the edge capping maximum from 100. Every pixel in the edge image whose value is above the edge capping minimum is set to the edge capping minimum. This effectively strengthens weaker edges (those below the edge capping minimum) because the entire image is scaled later.
Image Thresholds (%)
These two values values govern the thresholding in step 4. All pixels above the image threshold maximum are set to the maximum, and all pixels below the image threshold minimum are set to 0. Much of the time these thresholds should be left at 100 and 0. However, there are times when it is useful to raise the minimum above zero to mask soft tissue regions, and lower the maximum from 100 to remove artificial edges, such as the end of a CT bone that is within the X-ray image.
Image Scale
This is the scale factor used in step 5.

The following parameters are used when comparing the processed X-ray image to the processed DRR image:

Image Fitness
Bright DRR Pixel Factor
This factor is a part of evaluating a bone pose by comparing the DRR image to the X-ray image. The fitness of a particular pixel is weighted by the intensity of the pixel in the DRR image. Once the raw fitness of a pixel is calculated (by finding the squared difference between the DRR value and the X-ray value) it is multiplied by the value: 1.0 + bright_factor * DRR_pixel_intensity. The default value is set to 0.0.
Bright DRR Pixel Threshold
Parameter used together with Difference Threshold parameter when evaluating a bone pose by comparing the DRR image to the X-ray image. The fitness of a particular pixel is weighted more heavily if the DRR pixel is bright and if the intensity is much different than the X-ray pixel's intensity. The raw fitness of a pixel is calculated by taking the squared difference between the DRR value and the X-ray value. The raw fitness is squared again if the DRR pixel's intensity is greater than the Bright DRR Pixel Threshold parameter and the difference between it and the X-ray pixel's intensity is greater that the Difference Threshold parameter. The default value is 128.0 and the range is from 0.0 to 255.0.
Difference Threshold
Parameter used together with Bright DRR Pixel Threshold parameter when evaluating a bone pose by comparing the DRR image to the X-ray image. The fitness of a particular pixel is weighted more heavily if the DRR pixel is bright and if the intensity is much different than the X-ray pixel's intensity. The raw fitness of a pixel is calculated by taking the squared difference between the DRR value and the X-ray value. The raw fitness is squared again if the DRR pixel's intensity is greater than the Bright DRR Pixel Threshold parameter and the difference between it and the X-ray pixel's intensity is greater that the Difference Threshold parameter. The default value is 75.0 and the range is from 0.0 to 255.0.
View Weight
This factor is used when evaluating a bone pose by comparing the DRR images to the X-ray images. It is the relative weight of the two views in the final image metric (0.0 = all view 1, 1.0 = all view 2). The default value is 0.5, which means to weigh each view equally. If you are tracking objects in single-plane image data (i.e., both views contain the same images), set this parameter to either 0.0 or 1.0 so that X4D will generate and evaluate DRRs for only one view, making the optimization twice as fast.
Retrieved from ""