When I first started digital art I just used the default setting of the program that I was using without thinking what would become of all my hard work in the future. The problem that I now have as a result is that my images (some) are of a low resolution. A lot of artist programs have the settings default for web viewing, and not for printing (as should be the case). However, if I resize the image, some quality reduction is suffered as a result.
I have decided to go ahead and make copies anyway and thus I can just resize the copy. I have also thought of just re-painting them using the re-sized copy as an image that can be traced. The problem is that even such a solution might result in a re-painted image not looking as nice as the original.
I do not believe that I need to post an example image, because my inquiry is in the general-sense terms only.
What does everyone else th ink? What would you do? Also, is there a non-destructive way to resize an image? What is the best lossless file format?
I'm not sure from your description whether you are referring to photos of subjects that you are using as references for painting, or.....whether they are photos that serve as archive files of your paintings, themselves.
I have often used quite low res images as references for painting. I think the secret is to NOT maintain the same resolution while you enlarge the image. I find that doing so tends to create a more blurrier, softer image. I allow the resolution to just drop, as worrisome as that may seem to be at first. I find that I can work more easily from a slightly pixelized image than from a soft-focus appearing one.
As Yorky mentioned, one cannot "build resolution into" an image that has not already had it scanned, or photographed into it. Increasing the resolution of an image in a photo program cannot improve the image that already exists, if it does not already have such high resolution in the original. In fact, sometimes it may serve to cause it to be a bit worse in quality.
To answer your question regarding resolution loss, and loss of detail. Jpeg images are "lossy" files. That means that each time you work on such an image and re-save it, it loses some "picture information". The more times you re-save it, the more information it loses.
On the other hand, Tiff (tagged image file format) images retain their image information no matter how many times such an image may be open, adjusted, and subsequently saved. We used tiff files in the printing industry for that very reason, as we were constantly modifying image files, and we couldn't tolerate a loss of quality after a number of modifications.