Photo enlargement, interpolation software and dpi

I am a 50 year old lady amateur of photography . I am now working on an édition project as a personal accomplishment. Tonight, as I was looking on Google for further information on interpolation and smart resizing or smart scale, I discover this website. I really appreciate the technical information that compares interpolation and sharpening methods!

I am working with a Panasonic Lumix DMC-FZ10 which is a 4 megapixel but really good quality Leica f2'8 luminous zoom lens. I can produce fantastic prints 5X7 but to stay with a 300 dpi resolution I have to enlarge and interpolate my files. I am working with Shortcut PhotoZoom, last version, which unfortunately does not satisfy me with artifacts around edges (that are visible on prints). I would like to ask 2 questions:

1) Where can I find an effective interpolation software ? This site probably uses one for the examples put online!

2) Could you tell me if I really need to keep a 300 dpi resolution for 8X10 - 11X14 and 12X16 enlargements to achieve the same sharpness and details of my 5X7, considering the viewing distance and the printing process which is from a lab using a frontier printer on fuji crystal? I guess that printing with giclee will allow lower resolution around 240 dpi..Am I right?

You should not be getting too many edge artifacts with PhotoZoom. Have you made sure to disable all sharpening until after the enlargement phase? This can dramatically increase the visibility of halo artifacts. Make sure and use RAW mode (if supplied), otherwise in-camera sharpening may be unavoidable to some degree. With JPEG files, make sure to reduce all in-camera sharpening options to a minimum. If you've tried all of this, you might also try genuine fractals.

If your 8x10in or 11x14in photo will be viewed at a greater distance than the 5x7in, then the answer is no, you do not need to have the same ppi resolution in this enlarged print. On the other hand, there is no substitute for a very high resolution image to begin with, which will always be sharper than a lower ppi counterpart.

You may also want to experiment with sharpening settings on the fuji frontier versus giclee, as the former may require slightly more aggressive settings to achieve the same sharpness. But you are right that in general a giclee-style print will not need to have as high of a ppi (although this also depends on canvas type and subject matter).

For more on this topic, please take a look at this site's tutorial on optimizing digital photo enlargement, and on image interpolation.