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Printing With Interpolation

Hopefully, I've convinced you that you do not need to create 1/2 Gigabyte, 2400 ppi files every time you want to scan a cabinet card.  You can scan at reasonable resolutions and get reasonable file sizes.  But, now that you have your 300 ppi scan, and you want to blow it up by some huge amount, how do you use the pixel interpolation to get the best looking print from the data that you have?

I do it in several ways, depending on the software I am using.

My first choice is to use Q-Image Pro.  With this software, I simply set the default pixel interpolation parameters to "maximum detail" and use a Lanczos filter (an interpolation method that is time consuming, but excellent).  Then all I need to do is select the image(s) that I want to print and the size to print it at, and the program takes care of assuring that the photo is resized to the appropriate number of pixels per inch for the print.  The 4 photos on one page which I printed and scanned were done using these settings in Q-Image.  Suffice it to say that if I am printing multiple photos on a page, or if I am printing something that needs good interpolation, I print it in Q-Image.  Below is a screen image of Q-Image for the page that I printed and scanned:

Essentially, you tell Q-Image what directory you want, and the size of the photos to print.  You'll notice in the lower right corner the box with the green writing which has interpolation.  Right click on this (or choose it from the Prints menus), and set it for maximum quality, Lanczos interpolation.  The program then resizes and interpolates the image to your printer's native resolution (720 ppi for my Epson 1270), and sends the file to the printer.  Thanks to Mike Chaney from Q-Image for the info.  Actually, one thing he pointed out that I had not noticed, is that the program lists your printer's native resolution above the sample print (upper right hand corner above).

If I could not do it that way, my next choice would be to use Picture Window.  After looking around the web, an e-mail to Mike Chaney at Q-Image, and looking around their web site a bit, I admit I would do things differently than I had done in the past.  If I was printing close to the size I was scanning, I would probably still just hit the print command and be done with it.  If I was enlarging, however, I would take the size of the image (in one dimension), and multiply it by the resolution of my printer (for mine, it is 720 ppi, not to be confused with the fact that it is a 1440 dpi printer, and no, I'm just not going there. . .).  So, for an 8x10" photo, I would plan on the 10" side being 7200 pixels (this is going to produce a big file, but I'm not going to save it).  To do this, I would use the Resize command, shown below.

The small picture to the left is the original, the large picture on the right is the enlargement, and the dialog box shows the resize command to make the larger picture from the smaller one.  The left column in the dialog box is the original information - the original photo is 218 pixels wide by 145 high.  The column on the right is used to resize the photo.  In this case, I set it to make a photo 10" wide, with a resolution of 300 ppi (Well, that's what I used to do, now I would set it to 720ppi, and it would have calculated the 7200 pixel width).    Note at the bottom the Interpolation Method box.  I set this to Lanczos 8x8, which is one of the best options.  If you want to learn more about the mechanics of the different pixel interpolation methods, go to the Picture Window website and open the white paper on image resampling (Acrobat reader is required, but the paper is free).  I had said here previously that I would have resized it to a pixel density of about 300 ppi at the size of the print I was making.  The folks at Q-Image argue that you should not do it, because the printer driver will then have to re-interpolate to the printer's native resolution, so why make it interpolate twice, which might soften the image more than necessary?  The native resolution of a printer will vary, although Q-Image reports that the native resolution of all Epson photo printers under Windows is 720 ppi.  Note that I would not save the file that I resized, since all I've done is a simple resizing of the original image, which I can redo quickly any time I want to print.  Why save the huge file when you have a small one that has all of the detail (remember, interpolation does not add information to the image, and that 8x10 print shown in the preview window of Q-Image totaled to 124 Mb worth of images).  Of course, I would have saved it immediately before resizing, to save all that other nice work I did.

Please note that I used to resize things to the 240-300 ppi range for the size print I was going to make, and then printed this image.  They came out perfectly fine, but why not take every advantage you can get in keeping that image sharp by interpolating to your printer's resolution.

Adobe Photoshop and Photoshop LE both have pixel interpolation options in the Image Size command.  Their best interpolation method is the bicubic method.  I assume Paint Shop Pro has something along these lines, but I have not used it (any comments from users?).

Finally, while Q-image is inexpensive, for those really on a budget, it is my understanding that Irfanview, a free photo viewer/editor, has the ability to resize and resample images using Lanczos interpolation.  I have not tried it yet and would be happy to hear from anyone who has experience with it.  This is on my to-do list to download and try so that I can report back here, but I keep asking myself "do I really need one more photo editor on my hard-disk?"

Whatever method you choose, I would encourage you to try scanning and printing using a couple of different methods and different resolutions.  See what works best for you.

I hope you have found this helpful!  I've seen many recommendations about scanning resolution, but I've really not seen someone visually demonstrate why they recommend what they do.  As always, please feel free to contact me should you have any questions or comments.

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