Does my photolab's printer interpolate enlargements?

[atanask]

Do the minilab photo printers interpolate? I'm especially interested in Konica Minolta R2 which has a native resolution of 400 PPI by exposing the paper with three color laser beams.

For example, I have a file with 3000x2000 pixels and want it printed at 30x20 cm (~ 11.8x7.8 inches).

In Photoshop image size dialog if I uncheck “Resample”, set width to 30 cm, I get a resolution of 254 PPI.

Will the minilab photo printer use the native 3000x2000 pixels with 254 pixels per inch (in which case 1 pixel will be exposed by more than 1 dot, or it will resample the file to 4724x3150 (plus some pixels to avoid rollpaper movement) and print with 400 PPI forming 400 pixels per inch?

Thanks for the help!

PS: I'm new here, came to the site by link from DPReview and found very useful tutorials.

[McQ]

Almost every photographic printer will perform some type of hardware interpolation if the input image does not exactly match the native PPI of the printer. The Konica Minolta R2 and other minilab printers are no exception. This will likely produce slightly better results than with photoshop's bicubic software interpolation without any sharpening. However, I personally prefer to send images to any photo lab using the native PPI of the printer so that I can have more control over the whole process. Results can be much better by performing this interpolation yourself because you can apply the sharpening after the image has been enlarged.

Also take a look at this website's page on optimizing digital photo enlargement for more details on this topic and how to sharpen properly.

[atanask]

Thank You, the sharpening is my concern indeed.
I rely on Photokit Sharpener.
For inkjet workflow I don't resample, just set the size and output sharpen according the resulting PPI.
For digilab worflow, I have to upsample to the printer dpi and then use corespoding contone output sharpen.
Thanks

[Allinthemind]

I can't speak for the photo minilab you indicate. Fuji Frontiers (which are very common in high-street print shops), not only interpolate, but also analyse the image for brightness, contrast and shapening and automatically adjust them. This is mostly historical to "Correct" amateur film shots.

You can ask the lab manager to turn off these settings. The software on the Fujis is called "Image intelligence".

Si