If you define "resizing" to mean that the pixel dimensions don't change (you do that when you uncheck the "resample image" box under Image > Image Size in Photoshop), then resizing within Photoshop will have no affect on the image. A two-inch wide image at 300 ppi looks the same as far as the internal workings of Photoshop are concerned as a 4-inch wide image at 150 ppi. Resampling will either add pixels (up sampling) or remove pixels (down sampling) from the image and therefore will change it.
In a message dated 9/23/2001 11:55:53 PM Pacific Daylight Time, TonySleep@halftone.co.uk writes:
On Fri, 7 Sep 2001 07:01:59 -0500 Gordon Potter (gordon-potter@home.com)
wrote:
> I have been told resampling is much more destructive to an image
> then resizing.
