Emgu CV Library Documentation
cvPyrDown Method (src, dst, filter)
NamespacesEmgu.CVCvInvokecvPyrDown(IntPtr, IntPtr, FILTER_TYPE)

www.emgu.com/wiki
Performs downsampling step of Gaussian pyramid decomposition. First it convolves source image with the specified filter and then downsamples the image by rejecting even rows and columns.
Declaration Syntax
C#Visual BasicVisual C++
public static void cvPyrDown(
	IntPtr src,
	IntPtr dst,
	FILTER_TYPE filter
)
Public Shared Sub cvPyrDown ( _
	src As IntPtr, _
	dst As IntPtr, _
	filter As FILTER_TYPE _
)
public:
static void cvPyrDown(
	IntPtr src, 
	IntPtr dst, 
	FILTER_TYPE filter
)
Parameters
src (IntPtr)
The source image.
dst (IntPtr)
The destination image, should have 2x smaller width and height than the source.
filter (FILTER_TYPE)
Type of the filter used for convolution; only CV_GAUSSIAN_5x5 is currently supported.

Assembly: Emgu.CV (Module: Emgu.CV) Version: 1.3.0.0 (1.3.0.0)