async createBlob(width, height, quality = 0.6) {
    const { canvas } = await this.createCanvas(width, height);
    const option = {
      type: this.info.blob.type,
      quality,
    };
    return canvas.convertToBlob(option);
  }
create OffscreenCanvas from Blob
@param width
@param height
@param quality
@returns