pyrDown

Image processingfunctionOpenCV 5.0.0

import { pyrDown } from '@banou/opencv-wasm'

Use after await initOpenCV(). See the initialization and named imports guide.

Explore visually: Gaussian and Laplacian pyramids →

A Gaussian pyramid keeps smaller, blurrier copies of an image. A Laplacian pyramid keeps the detail lost between those copies, plus the smallest copy needed to rebuild the image.

VISUAL WALKTHROUGHFiltering

REFERENCE INPUTOriginal: broad shapes + fine stripes

Watch the thin stripes inside the rectangle. Shrinking removes their contrast while the larger shapes remain recognizable.

→

RESULTRebuild: enlarge, add detail, repeat

Start with the saved G2. Expand it and add L1 to recover G1; expand again and add L0 to recover G0. Enlarging alone leaves a blur. Adding the stored signed detail bands restores every original sample in this floating-point example.

Computed 32 × 24 example using the OpenCV pyramid kernel, checked against native pyrDown/pyrUp. Detail-band colour is amplified 3× for visibility; the stored values keep their signs and are never clipped.

imgproc_misc

example: samples/cpp/tutorial_code/ImgProc/Pyramids/Pyramids.cpp An example using pyrDown and pyrUp functions Blurs an image and downsamples it.

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

\begin{array}{l} | \texttt{dstsize.width} *2-src.cols| \leq 2 \\ | \texttt{dstsize.height} *2-src.rows| \leq 2 \end{array}

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

\frac{1}{256} \begin{bmatrix} 1 & 4 & 6 & 4 & 1  \\ 4 & 16 & 24 & 16 & 4  \\ 6 & 24 & 36 & 24 & 6  \\ 4 & 16 & 24 & 16 & 4  \\ 1 & 4 & 6 & 4 & 1 \end{bmatrix}

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

pyrDown(src: Mat, dst: Mat, dstsize: Size, borderType: number): void;

3 available overloads

pyrDown(src: Mat, dst: Mat): void;

pyrDown(src: Mat, dst: Mat, dstsize: Size): void;

pyrDown(src: Mat, dst: Mat, dstsize: Size, borderType: number): void;

src

input image.

dst

Output destination, filled by the native operation. output image; it has the specified size and the same type as src.

dstsize

size of the output image.

borderType

Pixel extrapolation method, see #BorderTypes (#BORDER_CONSTANT isn't supported)

Upstream declaration ↗

These signatures describe this package. Upstream documentation can mention optional backends that are absent from this build. Check runtime compatibility before choosing a backend or file format.