Hi,
I’m trying to downsample an image to 50*50*50 and then upsample it back to the original size. After I processed this with two ResampleImageFilter, the new upsampled image has 2*z_size*y_size black/empty pixels at the end of x-direction.
Original look:
Any idea what could lead to this problem? Thanks a lot!
You might be assuming that pixel coordinates are in the corner. They are at the center of the pixel. You might need to adjust your math to account for this.
Thanks for the quick reply. In my case, the origin of these 3 images are the same. If I understand correctly, for the upsampled image it should have the same size and physical coordinates as the original image. Am I correct?
What is the original resolution? Can you share your code?
Hi, here is the code
// GET ORIGINAL IMAGE INFO
auto inputImage = imageAReader->GetOutput();
auto outputOrigin = inputImage->GetOrigin();
auto outputDirection= inputImage->GetDirection();
auto inputSizePixels = inputImage->GetLargestPossibleRegion().GetSize();//[279,212,89]
auto inputSpacing = inputImage->GetSpacing();
double inputSize[3] = {inputSpacing[0] * inputSizePixels[0],
inputSpacing[1] * inputSizePixels[1],
inputSpacing[2] * inputSizePixels[2]};
auto _pTransform = T_Transform::New();
_pTransform->SetIdentity();
typename InterpolatorType::Pointer interpolator = BSplineInterpolatorType::New();
// DOWNSAMPLING
auto imageResampleFilterD = ResampleImageFilterType::New();
typename ImageType::SizeType outputSizeD = {static_cast<SizeValueType>(50),static_cast<SizeValueType>(50),static_cast<SizeValueType>(50)};
typename ImageType::SpacingType outputSpacingD;
outputSpacingD[0] = inputSize[0] / static_cast<float>(50);
outputSpacingD[1] = inputSize[1] / static_cast<float>(50);
outputSpacingD[2] = inputSize[2] / static_cast<float>(50);
imageResampleFilterD->SetInput(imageAReader->GetOutput());
imageResampleFilterD->SetOutputOrigin(outputOrigin);
imageResampleFilterD->SetOutputSpacing(outputSpacingD);
imageResampleFilterD->SetOutputDirection(outputDirection);
imageResampleFilterD->SetInterpolator(interpolator);
imageResampleFilterD->SetSize(outputSizeD);
imageResampleFilterD->SetTransform(_pTransform);
imageResampleFilterD->Update();
// UPSAMPLING
auto imageResampleFilterU = ResampleImageFilterType::New();
imageResampleFilterU->SetInput(imageResampleFilterD->GetOutput());
imageResampleFilterU->SetOutputOrigin(outputOrigin);
imageResampleFilterU->SetOutputSpacing(inputSpacing);
imageResampleFilterU->SetOutputDirection(outputDirection);
imageResampleFilterU->SetInterpolator(interpolator);
imageResampleFilterU->SetSize(inputSizePixels);
imageResampleFilterU->SetTransform(_pTransform);
imageResampleFilterU->Update();
Consider 1D case of 8 pixels:
You need to adjust the origin to keep the same image extent. This becomes obvious when you go back to your original image grid.
Thanks a lot! This explains why in our case we lost some image data. I’ll try to adjust the origin for each resample processes. Thanks again for your help🙌
