This post is a little sidetrack. There have been some questions on the QuiltArt list about the possibility of people "stealing" images from web sites and blogs and using them for nefarious and commercial purposes. One person pointed out that such low resolution images are not very useful for commercial purposes, so they were not worried. Another chimed in that it is quite easy to increase the resolution with "a good graphics program," therefore making such theft quite possible.
I was taught that while it is possible to increase the resolution of an image in Photoshop, it accomplishes little in terms of producing a usable high resolution image, because the program only guesses at what the missing detail would be. I was so indoctrinated in this belief that I have stood by it staunchly. I also hear that increasing the resolution in increments produces better results than simply increasing it in one step. I decided to do a little experiment and share it here.
Figure 1. This is the image I started with, scanned, full size at 72 ppi.
Figure 2. This is the same image reduced to 30 ppi. Really terrible isn't it? You can see the individual pixels at this resolution.
Figure 3. This is the 30 ppi image, increased back to 72 ppi in one step. It smoothes out the pixelation through the process of interpolation, but much of the detail has been lost—for example none of the stitching which you could see in the original has been restored and it's all pretty fuzzy.
Figure 4. This is the 30 ppi image restored to 72 ppi in 4 steps, about 10 ppi per step. I can't really see any difference between this one and the last.
So my conclusion is that what I was taught stands. I don't think increasing resolution by any method (at least in Photoshop) produces a high quality image. And I continue to be unconcerned about the possibility that someone will steal my quilts to print posters and coffee mugs.