constructor({ data }) {
    super({ name: 'pHYs', data });
    const dv = new DataView(data);
    defineDataViewProperty(this, 'pixelsPerUnitX', dv, 32, 0);
    defineDataViewProperty(this, 'pixelsPerUnitY', dv, 32, 4);
    defineDataViewProperty(this, 'unit', dv, 8, 8);
  }
A pHYs chunk containing physical pixel dimensions.