Image

老猫10/22/22About 3 min

Image

Bitmap wrapper backed by OpenCV Mat. Instances are produced from readImage, decodeImage, loadImage, Image.ofBitmap, or by wrapping an existing cv.Mat.

Call recycle() when you are finished to release native memory promptly.

Constructors

constructor

Accessors

Methods

Constructors

constructor

• new Image(mat)

Wrap an existing OpenCV matrix.

Parameters

Name	Type	Description
`mat`	`cv.Mat`	Source image.

Accessors

mat

• get mat(): cv.Mat

Underlying cv.Mat in the image’s native channel layout (often BGR or BGRA).

Returns

cv.Mat

c4mat

• get c4mat(): cv.Mat

4-channel BGRA view. Converts automatically when the source has fewer channels.

Returns

cv.Mat

width

• get width(): number

Image width in pixels.

Example

"nodejs";
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  console.log("width:", img.width);
}
main();

Returns

number

height

• get height(): number

Image height in pixels.

Example

"nodejs";
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  console.log("height:", img.height);
}
main();

Returns

number

Methods

pixel

▸ pixel(x, y): Color

Sample (x, y) as a Color. Interpretation:

3 channels — assumed BGR
4 channels — assumed BGRA
1 channel — grayscale

Example

"nodejs";
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const color = img.pixel(0, 0);
  console.log("top-left:", color);
}
main();

Parameters

Name	Type	Description
`x`	`number`	Column index, 0 = left.
`y`	`number`	Row index, 0 = top.

Returns

Color

clip

▸ clip(rect): Promise<Image>

Async ROI crop.

Example

"nodejs";
const cv = require("@autojs/opencv");
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const clipped = await img.clip(new cv.Rect(0, 0, 100, 100));
  console.log("clipped:", clipped);
}
main();

Parameters

Name	Type	Description
`rect`	`cv.Rect`	`x, y, width, height`.

Returns

Promise<Image>

clipSync

▸ clipSync(rect): Image

Synchronous clip.

Example

"nodejs";
const cv = require("@autojs/opencv");
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const clipped = img.clipSync(new cv.Rect(0, 0, 100, 100));
  console.log("clipped:", clipped);
}
main();

Parameters

Name	Type	Description
`rect`	`cv.Rect`	ROI.

Returns

Image

resize

▸ resize(width, height, interpolation?): Promise<Image>

Resize to an explicit width × height.

Parameters

Name	Type	Default	Description
`width`	`number`	`undefined`	Target width (px).
`height`	`number`	`undefined`	Target height (px).
`interpolation`	`number`	`cv.INTER_LINEAR`	OpenCV interpolation flag (`INTER_AREA`, `INTER_CUBIC`, `INTER_LANCZOS4`, `INTER_LINEAR`, `INTER_NEAREST`, …).

Returns

Promise<Image>

resizeSync

▸ resizeSync(width, height, interpolation?): Image

Synchronous resize.

Parameters

Name	Type	Default	Description
`width`	`number`	`undefined`	Target width.
`height`	`number`	`undefined`	Target height.
`interpolation`	`number`	`cv.INTER_LINEAR`	Interpolation flag.

Returns

Image

scale

▸ scale(fx, fy?, interpolation?): Promise<Image>

Uniform or independent scale factors relative to the current size (not absolute pixels).

Example

"nodejs";
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const scaled = await img.scale(0.5, 0.5);
  console.log("scaled:", scaled);
}
main();

Parameters

Name	Type	Default	Description
`fx`	`number`	`undefined`	Horizontal scale (1 = original, 0.5 = half width, 2 = double).
`fy`	`number`	`fx`	Vertical scale; defaults to `fx`.
`interpolation`	`number`	`cv.INTER_LINEAR`	Interpolation flag (same set as `resize`).

Returns

Promise<Image>

scaleSync

▸ scaleSync(fx, fy?, interpolation?): Image

Synchronous scale.

Parameters

Name	Type	Default	Description
`fx`	`number`	`undefined`	Horizontal factor.
`fy`	`number`	`fx`	Vertical factor.
`interpolation`	`number`	`cv.INTER_LINEAR`	Interpolation flag.

Returns

Image

rotate

▸ rotate(degree, center?): Promise<Image>

Rotate by degree around center (defaults to image center). Positive angles follow the implementation’s OpenCV convention (see upstream docs for your build).

Example

"nodejs";
const cv = require("@autojs/opencv");
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const rotated = await img.rotate(90);
  console.log("rotated:", rotated);
}
main();

Parameters

Name	Type	Description
`degree`	`number`	Angle in degrees.
`center`	`cv.Point2`	Optional pivot; image center if omitted.

Returns

Promise<Image>

rotateSync

▸ rotateSync(degree, center?): Image

Synchronous rotate.

Parameters

Name	Type	Description
`degree`	`number`	Degrees.
`center`	`cv.Point2`	Pivot.

Returns

Image

grayscale

▸ grayscale(): Promise<Image>

Async single-channel conversion.

Example

"nodejs";
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const gray = await img.grayscale();
  console.log("grayscale:", gray);
}
main();

Returns

Promise<Image>

grayscaleSync

▸ grayscaleSync(): Image

Synchronous grayscale.

Returns

Image

copy

▸ copy(): Promise<Image>

Deep copy into a new Image.

Example

"nodejs";
const { loadImage } = require("image");

async function main() {
  const img = await loadImage("https://picsum.photos/200/300");
  const copied = await img.copy();
  console.log("copy:", copied);
}
main();

Returns

Promise<Image>

copySync

▸ copySync(): Image

Synchronous copy.

Returns

Image

toBitmap

▸ toBitmap(): android.graphics.Bitmap

Export to an Android Bitmap.

See also

Bitmap

Returns

android.graphics.Bitmap

detectAndComputeFeatures

▸ detectAndComputeFeatures(options?): Promise<ImageFeatures>

Run feature detection + descriptor extraction for template / feature matching workflows.

Example

"nodejs";
const { readImage, FeatureDetectMethod } = require("image");

async function main() {
  const img = await readImage("./image.png");
  const features = await img.detectAndComputeFeatures({
    method: FeatureDetectMethod.SIFT,
    scale: 0.5,
  });

  features.recycle();
}
main();

Parameters

Name	Type	Description
`options`	`DetectAndComputeFeaturesOptions`	Detector tuning (method, scale, ROI, …).

Returns

Promise<ImageFeatures>

recycle

▸ recycle(): void

Release native buffers. Do not touch the wrapper afterwards.

Important

Image instances can be large—recycle() eagerly to avoid OOM pressure.

Example

"nodejs";
const { readImage } = require("image");

async function main() {
  const img = await readImage("./image.png");

  const gray = await img.grayscale();

  img.recycle();
  gray.recycle();
}
main();

Returns

void

ofBitmap

▸ Static ofBitmap(bitmap): Image

Wrap an android.graphics.Bitmap.

Example

"nodejs";
const { Image } = require("image");

const bitmap = /* ... */;
const img = Image.ofBitmap(bitmap);
console.log("from bitmap:", img);

Parameters

Name	Type	Description
`bitmap`	`android.graphics.Bitmap`	Valid bitmap.

Returns

Image

Throws

If bitmap is null or not a bitmap instance.