I'm trying to create a facebook cover photo (815x315 px - 72resolution ) from a poster I created (3300x5100px - 300resolution). Ive tried changing the canvas size to match the cover photo, tried resizing the image etc but each time the text, images, etc get super grainy when I downscale them. Any way I can downscale everything without losing quality? I just dont want to have to RECREATE the whole image just in different dimensions.
Can you give exact steps to reproduce this? Please include file details -size, color profiles, color mode, and can you include the original image at all? Can't reproduce what you are seeing with the steps given.
One thing: when you go from 3300 pixels to 315, you will lose image quality because you are reducing it to less than a tenth of its original size and you are changing to less resolution by going from 300 dpi to 72.