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The images on the prior page were simply enlarged and then resized to 4x6" 72 ppi images.  In addition to the display, I printed the enlargements at 4x5" each for the 300-2400 ppi images.  The images were enlarged the same amount as those on the prior page, but I cropped 1" of the width so I could fit four images on an 8.5x11" sheet of paper.  I then printed the images on an Epson 1270 printer, set to its highest quality setting.  Printing was handled through Q-image, set to the best print quality with Lanczos interpolation.  Based upon the degree of enlargement, and the scanning resolution, the prints were produced at the following pixel density:

Original Scan Resolution Pixels Per Inch on Print
2400 ppi 283 ppi
1200 ppi 142 ppi
600 ppi 72 ppi
300 ppi 36 ppi

There were a sparse number of pixels on the 300 ppi print!  It also goes to show you why you don't ordinarily want to make super huge enlargements.  The 300ppi scan did not do too badly on the print test, however (thanks to a good interpolation algorithm).  Take a look at the print below.  The file name to the left has the scan resolution in it.

Again, the 300 ppi looks a little grainier, but looking with a loupe, I could not convince myself that I could see any further detail on the higher resolution scans.

Don't believe me?  Download it and print it yourself.  I have the entire 8x11" scan done at 300 ppi available for download, in high quality jpeg.  Caution: it is over 2 Mb, which means some download time.  The easiest way to get it is to right click on this link, and hit "save link as".

So, after all this, what resolution should you scan at?  I'll let you decide.  You have seen what I do for my own photos - I scan almost everything at 300 ppi, with the very rare small photo at 600 ppi, where file size will not be as much of an issue and I might be more likely to enlarge the image.  Also, I tend to try and avoid enlarging anything over about twice its original size, although as you can see in this torture test you can get away with more.  Usually I don't need to enlarge more than twice the original size, but it can happen when you crop a small area of the photo as we did here.  Even with a 2400 ppi scan, you can see the images are quite soft.  You don't see a good sharp image.  Using the unsharp mask command would help somewhat, but it still would not add detail to the image, and I would still not consider the image detailed enough to consider printing as is.  So in addition to thinking about scanning resolution, you want to think about how much you can reasonably enlarge the image.

Well, I had originally ended the case study at this point.  However, I've realized that while I've demonstrated how the images look after scanning them at different scanning settings and printing them, I have not demonstrated how to print them so that you get the best interpolation.  If you know how to do it, you're done.  If not, go on to the next page, and I'll show you a couple of ways to do it.

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