code: function getTextImage(imageId) {
      const width = SIZE;
      const height = SIZE;
  
      const tokens = imageId.substring(12).split(':');
      const l = tokens[0];
      const bg = tokens[1];
      const pixelData = createTextPixelData(l, bg);
  
      function getPixelData() {
        return pixelData;
      }
  
      const image = {
        imageId,
        minPixelValue: 0,
        maxPixelValue: 257,
        slope: 1.0,
        intercept: 0,
        windowCenter: 127,
        windowWidth: 256,
        render: cs.renderGrayscaleImage,
        getPixelData,
        rows: height,
        columns: width,
        height,
        width,
        color: false,
        columnPixelSpacing: 1.0,
        rowPixelSpacing: 1.0,
        invert: false,
        sizeInBytes: width * height
      };
  
      return {
        promise: new Promise((resolve) => {
          resolve(image);
        }),
        cancelFn: undefined
      };
    }
docs: ImageId should be // example-n://<label>:<bg-color>