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It is my understanding that it is always better to duplicate content then to remove it. When something is upscaled nothing is lost. When something is downscaled content IS lost.

Unless your output resolution is an exact multiple of the input resolution then you're doing interpolation. You've not exactly lost anything but you're not getting what you put in. What you have to do is trust the upscalers algorithms to do it the "right" way. The more you pay, the better in theory the algorithms inside the upscaler. Your monitor/TV will already have an upscaler inside but your super expensive external box will hopefully do a better job.

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While artifacts are an issue with both processes I think it is felt that the end result is almost always better when upscaling as opposed to downscaling. It is the loss of content that makes the downscaling process more difficult. I don’t mean in it’s simpliest form of just removing pixels but when it is done with picture quality in mind. In order to minimize the effect of downscaling the processor must have the ability to work in an adaptive manner to produce a picture that is still pleasing to the eye. When upscaling I don’t think the task is quite as difficult. It is this complexity that places me in the buy a decent player with a good scaler camp.

Up and down scaling both require interpolation which gets pretty complicated. A naive implementation would be to just duplicate or remove rows. It'll do the job but it'll look terrible.