@allmaps/stdlib/dist/background-color.js

Allmaps Standard Library

const DEFAULT_BIN_SIZE = 5;
const DEFAULT_RESOLUTION = 2;
export function getImageData(imageBitmap, mask) {
    const canvas = new OffscreenCanvas(imageBitmap.width, imageBitmap.height);
    const context = canvas.getContext('2d');
    if (!context) {
        throw new Error('Could not create OffscreenCanvas context');
    }
    if (mask) {
        context.fillStyle = 'rgba(0, 0, 0, 0)';
        context.fillRect(0, 0, imageBitmap.width, imageBitmap.height);
        context.beginPath();
        context.moveTo(mask[0][0], mask[0][1]);
        mask.slice(1).forEach((point) => context.lineTo(point[0], point[1]));
        context.closePath();
        context.clip();
    }
    context.drawImage(imageBitmap, 0, 0);
    return context.getImageData(0, 0, imageBitmap.width, imageBitmap.height);
}
export function getColorsArray(imageData, resolution = DEFAULT_RESOLUTION) {
    const colors = [];
    for (let x = 0; x < imageData.width; x += resolution) {
        for (let y = 0; y < imageData.height; y += resolution) {
            const startIndex = (x + y * imageData.width) * 4;
            const opacity = imageData.data[startIndex + 3];
            if (opacity > 0) {
                const color = [
                    imageData.data[startIndex],
                    imageData.data[startIndex + 1],
                    imageData.data[startIndex + 2]
                ];
                colors.push(color);
            }
        }
    }
    return colors;
}
export function getColorHistogram(colors, binSize = DEFAULT_BIN_SIZE) {
    const histogram = {};
    for (const color of colors) {
        const bin = createColorBin(color, binSize);
        if (!histogram[bin]) {
            histogram[bin] = {
                count: 0,
                color
            };
        }
        histogram[bin].count += 1;
    }
    return histogram;
}
export function getMaxOccurringColor(histogram) {
    let max = Number.NEGATIVE_INFINITY;
    let maxOccurringColor;
    for (const { count, color } of Object.values(histogram)) {
        if (count > max) {
            max = count;
            maxOccurringColor = color;
        }
    }
    if (!maxOccurringColor) {
        throw new Error('Histogram is empty');
    }
    return {
        count: max,
        color: maxOccurringColor
    };
}
function createColorBin(color, binSize) {
    return color.map((c) => Math.round(c / binSize)).toString();
}