tom-weatherhead/thaw-image-processing.ts

// thaw-image-processing.ts/src/desaturate.ts

import { ColourModel, IThAWImage, ThAWImageBufferType } from '../util/image';

import { mapColoursInImageFromBuffer } from '../util/map-colours';

export function desaturateRGBA(
    buffer: ThAWImageBufferType,
    offset: number
): void {
    // Assuming that buffer[offset] is the red byte, buffer[offset + 1] is the green byte, and buffer[offset + 2] is the blue byte.
    const grey = Math.round(
        buffer[offset] * 0.3 +
            buffer[offset + 1] * 0.59 +
            buffer[offset + 2] * 0.11
    );

    buffer[offset + 2] = grey;
    buffer[offset + 1] = grey;
    buffer[offset] = grey;
}

export function desaturateImage(srcImage: IThAWImage): IThAWImage {
    if (srcImage.colourModel !== ColourModel.RGBA32) {
        throw new Error('desaturateImage: Unsupported colour model');
    }
    return mapColoursInImageFromBuffer(srcImage, desaturateRGBA);
}

export function rotateColourChannelsRGBA(
    buffer: ThAWImageBufferType,
    offset: number
): void {
    const temp = buffer[offset];

    buffer[offset] = buffer[offset + 1];
    buffer[offset + 1] = buffer[offset + 2];
    buffer[offset + 2] = temp;

    // buffer[offset + 3] is the alpha channel; do not change it.
}

export function rotateColourChannelsInImage(
    srcImage: IThAWImage
): IThAWImage {
    if (srcImage.colourModel !== ColourModel.RGBA32) {
        throw new Error(
            'rotateColourChannelsInImage: Unsupported colour model'
        );
    }
    return mapColoursInImageFromBuffer(srcImage, rotateColourChannelsRGBA);
}