When scaling up an image is scaled with nearest / point sampling. Gives a sharper result but may not look as nice.
When scaling down an image is scaled with bilinear / smooth sampling. Gives a more smooth result as each resultant pixel is sampled from the surrounding 4 pixels of the source sample point. Fastest for scaling up images to larger sizes.
Even better than Smooth sampling. Cubic sampling produces better images when they are scaled down to a smaller sizes.
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