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Photography Question 
Andrew Collett

How Large Can An 8.0 Megapixel File Be Printed?

Hello, I was wondering if anyone had any experience with inlarging files from an 8.0 megapixel camera for printing as fine art prints? I would like to print some files up to a maximum of 20x30 but am worried about a loss of sharpness. I am currently using Photoshop CS.

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10/12/2004 5:32:54 AM

David King   Hi Andrew,

As a starting point, take the pixel dimension of a side, divide it by the file resolution that gives you the best print quality on your printer (NOT the printer's resolution) and that will give you the linear dimension of the native sized print from your file.

To enlarge beyond that size there are a number of techniques that can give pretty good results up to a point. One is to use PS's resizing to increase pixel dimensions in 10% increments. It may take a number of repeats, but this will hold the picture together pretty well for up to a 4-5 times (area) enlargement. Plugins like Genuine Fractals will take it up even farther with excellent results. Some printing algorithyms such a Q-Image allow even greater enlargement and enlarge far better than PS.

In all cases, wait until the last step with the file at full size to do any sharpening. If you sharpen too soon, the false edging created by the unsharp masking technique are also enlarged and contribute to the "digital look" so common in many digital prints.

If your files are very sharp to begin with (shot at the lenses "sweet spot" with a very steady tripod and no movement, and carefully focussed) you can easily get a terrific results at 16x20 or a little larger. For poster sized prints, try this technique...

Make the absolute very best print you can at the native size at 300-360 dpi.(usually around 8x10 or a little smaller). Use a VERY GOOD scanner with a large dynamic range (3.6 or better) and at least 16-bit per channel and make a good, profiled scan of the image at the best optical resolution possible. This will create a VERY large file, perhaps over 600 megabytes, but it will be astonishingly good. From that you can reduce it to your printing size and go from there. I've seen posters made from 5 megapixel images and 500 megabyte files that were astonishing in quality.


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10/17/2004 1:43:56 PM

Andrew Collett   David, thank you for taking the time to answer my question. The information you gave is very helpful.

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10/17/2004 1:49:17 PM


BetterPhoto Member Since: 10/28/2003

Why do you have to keep increasing at 10%? Why can't you just resize once?


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10/18/2004 5:31:34 AM

David King   Hi Jerry,

it is all about the math. Remember digital is nothing but math. Anytime the computer resizes an image it has to either create or throw away data, i.e. it 'guesses' at what should be created or tossed. The easier the math is for the algorithym and the smaller the increments (meaning the fewer pixels that will have to be interpolated or extrapolated) the more accurate the result. 10% is incredibly easy math for it; fore xample, it creates only one new pixel for every ten it can evaluate.

If it has to make big guesses about what is OK to keep or what needs to be added, then its guessing is less precise. if it had to add every other pixel for example, would it make good decisions on the 'between' data or if a run of like pixles should be extended or cut off? The answer is, "sometimes, sometimes not..." When you make big jumps you can really see the difference in quality in a high resolution print even though the monitor, showing at 72 ppi may not indicate it as well.

The bicubic approach to sizing is not new technology; I'm surprised it has been retained when other areas of PS have seen major improvement and there are clearly other approaches out there that yield better results.


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10/18/2004 8:00:04 AM

Peter K. Burian
BetterPhoto Member Since: 4/8/2004
  Andrew: If you have Photoshop CS, use the Bicubic Smoother option when increasing file size.

This new alogrithm is so good, you can make major jumps in one shot.

Peter Burian

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10/20/2004 5:33:01 AM

Andrew Collett   Thank you for the feedback Peter, I really appreciate it.

Do you think it is possible to enlarge a photo say 50% and still hold enough sharpness to produce a fine art print? I know there are many other factors envoled but assume the original image is spot on to begin with.

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10/28/2004 2:28:15 AM

David King   Hi again Andrew.

Assuming that the original image is tack sharp (and that is a MAJOR requirement) then I've had no difficulty making 13x19 prints from 5-meg and 6-meg camera originals. Comparatively speaking, although I continually hear how good it is, I'm not that impressed with the new bicubic algorithyms in PS which, while better than before are still crude compared to some others available. Consider "Q-Image" as a printing package. Though it was designed for creating picture packages for wedding and portrait photographers, it also has one of the best resizing technologies going and produces extremely good enlargements. And, as I mentioned earlier, when I'm making really large prints (20 x 24 or 24 x 36 for example) doing the described scanner routine results in prints that hold together as if they were much smaller enlargements.

One thing worth repeating for emphasis though, is if you plan on going big, WAIT to do any sharpening until the photo file is at the large printing dimensions; otherwise you also enlarge the sharpening artifacts. The big give-away for poorly done digital prints is that over-sharpened haloing.


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10/28/2004 8:44:37 AM

Andrew Collett   Thanks David, I really appreciate your help with this matter.

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10/28/2004 10:47:17 AM

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