Resizing images - jaggy avoidance

[dmsims]

Original source is a high quality scan of a slide (top right)

I want to resize these to 1920px but no matter what program / setting I use it always pixelates the lines (see the line of the blonde's swimsuit)

Any suggestions (or is it just normal?)

[SCEtoAUX]

That's antialiasing/resampling for you.

It will be happening to the entire image but the highest contrast area shows it most.

Try blow up by Alien Skin (think it's called that) It does some clever thingsand might help. There's a free trial.