subtract

Core and matricesfunctionOpenCV 5.0.0

import { subtract } 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.

Calculates the per-element difference between two arrays or array and a scalar.

The function subtract calculates:

Difference between two arrays, when both input arrays have the same size and the same number of channels:

\texttt{dst}(I) =  \texttt{saturate} ( \texttt{src1}(I) -  \texttt{src2}(I)) \quad \texttt{if mask}(I) \ne0

Difference between an array and a scalar, when src2 is constructed from Scalar or has the same number of elements as src1.channels():

\texttt{dst}(I) =  \texttt{saturate} ( \texttt{src1}(I) -  \texttt{src2} ) \quad \texttt{if mask}(I) \ne0

Difference between a scalar and an array, when src1 is constructed from Scalar or has the same number of elements as src2.channels():

\texttt{dst}(I) =  \texttt{saturate} ( \texttt{src1} -  \texttt{src2}(I) ) \quad \texttt{if mask}(I) \ne0

The reverse difference between a scalar and an array in the case of SubRS:

\texttt{dst}(I) =  \texttt{saturate} ( \texttt{src2} -  \texttt{src1}(I) ) \quad \texttt{if mask}(I) \ne0

where I is a multi-dimensional index of array elements. In case of multi-channel arrays, each channel is processed independently.

The first function in the list above can be replaced with matrix expressions:

    dst = src1 - src2;
    dst -= src1; // equivalent to subtract(dst, src1, dst);

The input arrays and the output array can all have the same or different depths. For example, you can subtract to 8-bit unsigned arrays and store the difference in a 16-bit signed array. Depth of the output array is determined by dtype parameter. In the second and third cases above, as well as in the first case, when src1.depth() == src2.depth(), dtype can be set to the default -1. In this case the output array will have the same depth as the input array, be it src1, src2 or both.

Note: Saturation is not applied when the output array has the depth CV_32S. You may even get result of an incorrect sign in the case of overflow.

Note: (Python) Be careful to difference behaviour between src1/src2 are single number and they are tuple/array. subtract(src,X) means subtract(src,(X,X,X,X)). subtract(src,(X,)) means subtract(src,(X,0,0,0)).

See: add, addWeighted, scaleAdd, Mat::convertTo

subtract(src1: Mat, src2: Mat, dst: Mat, mask: Mat, dtype: number): void;

3 available overloads

subtract(src1: Mat, src2: Mat, dst: Mat): void;

subtract(src1: Mat, src2: Mat, dst: Mat, mask: Mat): void;

subtract(src1: Mat, src2: Mat, dst: Mat, mask: Mat, dtype: number): void;

src1: first input array or a scalar.
src2: second input array or a scalar.
dst: Output destination, filled by the native operation. output array of the same size and the same number of channels as the input array.
mask: optional operation mask; this is CV_8U, CV8S or CV_Bool single channel array that specifies elements of the output array to be changed.
dtype: optional depth of the output array

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.