How to Downsample The Chrominance Components So I am doing an image compression project for college and am trying to create a visual demonstration of how downsampling chrominance components can reduce the amount of digital information while being hardly noticeable to the average person. While doing research for this project, I came across this video where the guy gives a demonstration of downsampling that leads to there being 100x less color in the image he uses as an example. I was hoping to do something similar but am unsure as to how he was able to downsample the chrominance components in an image by a factor of 10x in each direction. 

Looking at the standard ratios for chroma subsampling(/downsampling) the best I could find seems to be 4:2:0 which would downsample the chrominance by a factor of 2x in each direction. It's possible that might be enough for a demonstration, but I was hoping I might could push it a little further. 

As a side question, does anyone have any recommendations as to how best to apply the downsampling color to my raw image? I have some ideas involving either photoshop or GIMP, but I was wondering if anybody had a better suggestion.
For demonstration purposes GIMP is just fine. It can split an image to three separate YUV/YCbCr images. You can then manually resize the UV/CbCr images by any amount to downsample the chroma. Then upsample back to original resolution and recombine the image again.