tips to enlarge images for offset printing in photoshop

Hi.

In offset, you need a 1.5 to 2 quality factor. That means, at minimum: 150 * 1.5 = 225 pixels per inch (final resolution).

Try to not use interpolation when you scale images. If is necessary to use interpolation, try "preserve details 2.0".

Maybe these links can be helpful:

https://helpx.adobe.com/photoshop/using/image-size-resolution.html

https://photoshopcafe.com/resize-images-photoshop-keep-quality/

Please show the actual image/s and give a meaningful explanation about the necessary print size. 

GIGO applies as usual, but some Resample Methods may provide more pleasing results (try the Preserve Details-ones) and sometimes adding noise can help »drown out« certain artefacts. 

What are the pixel dimensions and intended printed dimensions for a typical image?