feat(pixel): add convolve() & preset kernels

thi-ng · Feb 26, 2021 · 6a31dc3 · 6a31dc3
1 parent eeb6396
commit 6a31dc3
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diff --git a/packages/pixel/src/convolve.ts b/packages/pixel/src/convolve.ts
@@ -0,0 +1,138 @@
+import { assert, Fn, Fn2, FnN, IObjectOf, NumericArray } from "@thi.ng/api";
+import { isFunction, isNumber } from "@thi.ng/checks";
+import { FloatBuffer } from "./float";
+import { FLOAT_GRAY } from "./format/float-gray";
+import { ensureChannel } from "./utils";
+
+export interface KernelSpec {
+    /**
+     * Kernel coefficients or factory function.
+     */
+    spec: NumericArray | Fn<FloatBuffer, FnN>;
+    /**
+     * Kernel size. If given as number, expands to `[size, size]`.
+     */
+    size: number | [number, number];
+}
+
+export interface ConvolveOpts {
+    /**
+     * Convolution kernel details/implementation.
+     */
+    kernel: KernelSpec;
+    /**
+     * Channel ID to convolve.
+     *
+     * @defaultValue 0
+     */
+    channel?: number;
+    /**
+     * If true, the result image will be same size as source image with empty
+     * (padded) border pixels.
+     *
+     * @defaultValue true
+     */
+    pad?: boolean;
+    /**
+     * Result scale factor
+     *
+     * @defaultValue 1
+     */
+    scale?: number;
+}
+
+/**
+ * Convolves a single channel from given `src` float buffer with provided
+ * kernel. Returns result as single channel buffer (in {@link FLOAT_GRAY}
+ * format).
+ *
+ * @param src
+ * @param opts
+ */
+export const convolve = (src: FloatBuffer, opts: ConvolveOpts) => {
+    const { kernel, channel, pad, scale } = {
+        channel: 0,
+        pad: true,
+        scale: 1,
+        ...opts,
+    };
+    ensureChannel(src.format, channel);
+    const size = kernel.size;
+    const [kw, kh] = isNumber(size) ? [size, size] : size;
+    const { width, height, stride, rowStride } = src;
+    assert(
+        kw >= 0 && kw <= width && kh >= 0 && kh <= height,
+        `invalid kernel size: ${size}`
+    );
+    const dwidth = pad ? width : width - kw + 1;
+    const dheight = pad ? height : height - kh + 1;
+    const dest = new FloatBuffer(dwidth, dheight, FLOAT_GRAY);
+    const dpix = dest.pixels;
+    let $kernel: FnN;
+    if (isFunction(kernel.spec)) {
+        $kernel = kernel.spec(src);
+    } else {
+        const k = FLOAT_KERNELS[`${kw}-${kh}`];
+        assert(!!k, `missing impl for given kernel size: ${size}`);
+        $kernel = k(src, kernel.spec);
+    }
+    const kh2 = kh >> 1;
+    const kw2 = kw >> 1;
+    const maxY = height - kh2;
+    const maxX = width - kw2;
+    for (let y = kh2; y < maxY; y++) {
+        for (
+            let x = kw2,
+                i = y * rowStride + x * stride + channel,
+                j = pad ? y * dwidth + x : (y - kh2) * dwidth;
+            x < maxX;
+            x++, i += stride, j++
+        ) {
+            dpix[j] = $kernel(i) * scale;
+        }
+    }
+    return dest;
+};
+
+const FLOAT_KERNELS: IObjectOf<Fn2<FloatBuffer, NumericArray, FnN>> = {
+    "3-3": (src, [a, b, c, d, e, f, g, h, i]) => {
+        const { pixels: pix, stride, rowStride } = src;
+        const y1 = rowStride + stride;
+        const y2 = rowStride - stride;
+        return (idx) =>
+            a * pix[idx - y1] +
+            b * pix[idx - rowStride] +
+            c * pix[idx - y2] +
+            d * pix[idx - stride] +
+            e * pix[idx] +
+            f * pix[idx + stride] +
+            g * pix[idx + y2] +
+            h * pix[idx + rowStride] +
+            i * pix[idx + y1];
+    },
+};
+
+export const SOBEL_X: KernelSpec = {
+    spec: [-1, -2, -1, 0, 0, 0, 1, 2, 1],
+    size: 3,
+};
+
+export const SOBEL_Y: KernelSpec = {
+    spec: [-1, 0, 1, -2, 0, 2, -1, 0, 1],
+    size: 3,
+};
+
+export const SHARPEN: KernelSpec = {
+    spec: [0, -1, 0, -1, 5, -1, 0, -1, 0],
+    size: 3,
+};
+
+export const BOX_BLUR3: KernelSpec = {
+    spec: [1 / 9, 1 / 9, 1 / 9, 1 / 9, 1 / 9, 1 / 9, 1 / 9, 1 / 9, 1 / 9],
+    size: 3,
+};
+
+export const GAUSSIAN_BLUR3: KernelSpec = {
+    spec: [1 / 16, 1 / 8, 1 / 16, 1 / 8, 1 / 4, 1 / 8, 1 / 16, 1 / 8, 1 / 16],
+    size: 3,
+};
diff --git a/packages/pixel/src/index.ts b/packages/pixel/src/index.ts
@@ -1,6 +1,7 @@
 export * from "./api";
 export * from "./canvas";
 export * from "./codegen";
+export * from "./convolve";
 export * from "./dither";
 export * from "./float";
 export * from "./gradient";