In a message dated 10/21/2001 9:54:44 PM Pacific Daylight Time, kdurling@earthlink.net writes:
How do you resize an image without losing/adding pixels? Just by
specifying the inch dimension? That's something I've never been clear
about - whether choosing inch, cm, pixels or whatever in the size
dialogue does anything different. It seems to this neophyte that they
are all terms for the same thing. Does the choice actually result in
different processes?
When using Photoshop, here's a hint: Photoshop only cares about the number of pixels it is working with. It will display the resolution in dpi and the physical size in inches, but it does that only for your benefit, for the printer's benefit, etc. But Photoshop itself doesn't use any of that information except for the pixel count. There is a box in Photoshop's Image Size dialog that allows you tell Photoshop that you don't want to resample (i.e., the pixel count is not to change). You can then change the physical dimensions (go from 2x4 inches to 8x16 inches, for example) and Photoshop will automatically change the resolution (say from 800 dpi to 200 dpi) to keep the number of pixels constant. If you tell Photoshop it's OK to change the pixel count, then you can change both the dimensions and the resolution to whatever you want, and the pixel count will change accordingly. In that case, Photoshop will upsample or downsmaple as re!
quired. The only thing that Photoshop does with the dimension information is send it to the printer. The printer cares about it, but Photoshop doesn't. I never worry about dpi or dimensions until I'm ready to print. The I assign the dimensions I want. I usually set the dpi to 300 for printing and resampling usually takes place then. But I save a PSD file with the original pixel count before I do that, so I always have the original data and don't lose any pixels if I need to go back and print another copy, maybe a larger one next time.
