Blurs an image and downsamples it

dst = cv.pyrDown(src)
dst = cv.pyrDown(src, 'OptionName',optionValue, ...)

Input

• src Input image; uint8, uint16, int16, single, or double.

Output

• dst Destination image. It has the specified size and the same type as src.

Options

• DstSize Size of the output image [w,h]. default [0,0], see below.
• BorderType Pixel extrapolation method, see cv.copyMakeBorder ('Constant' isn't supported). Default 'Default'

By default, size of the output image is computed as [(size(src,2)+1)/2 (size(src,1)+1)/2], but in any case, the following conditions should be satisfied:

abs(DstSize(2)*2 - size(src,2)) <= 2
abs(DstSize(1)*2 - size(src,1)) <= 2

The function performs the downsampling step of the Gaussian pyramid construction. First, it convolves the source image with the kernel:

1/256 * [1  4  6  4  1;
         4 16 24 16  4;
         6 24 34 24  6;
         4 16 24 16  4;
         1  4  6  4  1]

Then, it downsamples the image by rejecting even rows and columns.