I use Gimp to make PNG cover banners for social media sites. I have a hard time getting a clear finish, my end product appears slightly cloudy.
I do my best to make small logos or letters in HD so when they're reduced they don't lose quality. Here are attachments to show what i mean with "cloudiness":
I do my best to make small logos or letters in HD so when they're reduced they don't lose quality.
Scaling down adds some blurriness (not as much as scaling up of course). After scaling down to the final size(*) it is often useful to add back some slight sharpening (Filters>Enhance>Unsharp mask).
Scaling down can also introduce moirÃ©s and jagged edges due to spatial frequency folding. This can be prevented by blurring the image before scaling down (in other words, to cut off the high frequencies). The usual ratio is to use a blur of X pixels if you downscale by X (ie, 2px if your final image is 50% of the original).
(*) hoping the host won't mercilessly rescale or recompress your image... re-download the image from it and compare to the one you uploaded...