I have, for example, a 1in x 1in image @250dpi that I want to scale to 6in x6in. I realize that it would automatically become a 40 dpi image, but if I make it 15% opacity, then is there a way I could keep it crisp? Technically the 15% opacity can be achieved by spacing the "dots" so that the image quality is not compromised.
Is this possible?
Opacity has nothing to do with the quality of the resampled image.
INteresting idea though. Technically it might be that you can achieve transparency by moving the dots further apart and having transparent space between them. But it isn't done that way, it's done by blending colours. And The image quality is compromised because it is bigger, you might as well say doubling up the dots would maintain quality. Perhaps at 15% opacity you will see so little if the image ut won't mattter...