code: func (i *Image) Dispose() error {
  	i.copyCheck()
  	if i.isDisposed() {
  		return nil
  	}
  	if i.isSubImage() {
  		return nil
  	}
  	i.mipmap.dispose()
  	i.resolvePendingPixels(false)
  	return nil
  }
docs: // Dispose disposes the image data. After disposing, most of image functions do nothing and returns meaningless values.
  //
  // Dispose is useful to save memory.
  //
  // When the image is disposed, Dipose does nothing.
  //
  // Dipose always return nil as of 1.5.0-alpha.