AdvancedImageToImageMetric, AdvancedMeanSquaresImageToImageMetric estimating min and max twice, redundantly

[N-Dekker]

Both AdvancedImageToImageMetric::Initialize() and AdvancedImageToImageMetric::InitializeLimiters() use ComputeImageExtremaFilter to estimate the minimum and the maximum pixel value of the fixed and the moving image. Now the first member function also calls the second one, indirectly, causing the expensive ComputeImageExtremaFilter to be executed more than necessary.

Looking back at commit 592608c (January 15, 2018), it looks like it it that way already for a while:

elastix/Common/CostFunctions/itkAdvancedImageToImageMetric.hxx

Lines 276 to 277 in 592608c

	this->m_FixedImageTrueMax = computeFixedImageExtrema->GetMaximum();
	this->m_FixedImageTrueMin = computeFixedImageExtrema->GetMinimum();

elastix/Components/Metrics/AdvancedMeanSquares/itkAdvancedMeanSquaresImageToImageMetric.hxx

Lines 94 to 95 in 592608c

	this->m_FixedImageTrueMax = computeFixedImageExtrema->GetMaximum();
	this->m_FixedImageTrueMin = computeFixedImageExtrema->GetMinimum();

While AdvancedMeanSquaresImageToImageMetric::Initialize() also calling AdvancedImageToImageMetric::Initialize():

elastix/Components/Metrics/AdvancedMeanSquares/itkAdvancedMeanSquaresImageToImageMetric.hxx

Line 68 in 592608c

Superclass::Initialize();