Bill Tuthill wrote:

I like Irfanview too -- it is a great image and slideshow viewer --
but it does not control chroma subsampling.

You can turn subsampling off in Irfanview by ticking an option during
saving.

I mainly find that useful when there are important red areas in an image,
because otherwise they come out very poorly in a JPEG.

I would agree with the person who said that Photoshop is amongst the worst
- I find I can always shrink a Photoshop-saved JPEG significantly by
running it through a lossless optimiser (such as Irfanview's) afterwards.