Instagram pixelating dslr images?

[Chuck]

Instagram resizes images as you upload them to 640x640 (before mid-2013 it was 612x612). It does not use a very robust resizing algorithm, so image quality can suffer (resulting in softness and/or the pixelation you describe).

You'll see (much) better results using your own software or app to resize (and optionally sharpen) your image to 640x640 before handing it off to the instagram app, since that will avoid their own resizing.

You can empirically prove this to yourself via some experiments -- take a highly-detailed image and upload it multiple times -- including full resolution and resize it (yourself) to various smaller sizes. You'll find resizing to 640x640 (and applying appropriate sharpening) will be the best result.

Keep an eye on the instagram API and blog for updates. They already stepped up from 612x612 to 640x640 in mid/late 2013 -- they might step up again. You'll always get the best results resizing outside of instagram, but you obviously want to resize to the highest resolution instagram supports.

You mention "changing the dpi" -- dpi is meaningless metadata for digital images. All that matters is the final image resolution -- in this case, you want 640x640.