How to do chroma sampling ?

How to do the chroma sampling similar to [ImageMagick](https://github.com/gographics/imagick/blob/v2.5.0/imagick/magick_wand_prop.go#L489) as mentioned below.

```
mw := imagick.NewMagickWand()
defer mw.Destroy()
samplingFactor := []float64{2, 1, 1}	
mw.SetSamplingFactors(samplingFactor)
```