Not Your Everyday Banana

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Possible Duplicate:
Is it possible to increase the pixel density of an image?
Is there a general formula for image size vs. print size?

Can one of the many photo editors max a photo automatically while preserving the same quality?

The answer is the max size a photo can be enlarged is the size of the original photo.

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marked as duplicate by mattdm, drewbenn, whuber, jrista Mar 10 '12 at 5:22

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
The title to this question and the body of the question itself seem to be two completely separate questions. –  mattdm Mar 4 '12 at 19:27
    
Another highly-related question: Is it possible to increase the pixel density of an image? –  mattdm Mar 4 '12 at 19:28
    
i'll just delete it since it's pretty much the same to the pixel density question. This question is phrased more clearly to how non-technical people would ask the question. Normal people won't know what pixel density is. Maybe ask a question on print quality/viewing distance and move the answer since it's still helpful to that type of question. –  designparadise Mar 7 '12 at 18:32
    
It's definitely useful to have not-deleted duplicate questions, but have the duplicates closed as pointing to the others. As you say, this helps with non-technical people searching for answers. My main confusion/complaint here as that there were two apparently-unrelated questions, one as the title of the question and the other as the body. That makes it hard to answer. –  mattdm Mar 7 '12 at 18:45
2  
@designparadise - I've rolled back your question for now and we'll let the community decide to close it or not. If you want to ask the question you changed it to, then please search to make sure it isn't asked first, and if not, open a new question. –  rfusca Mar 7 '12 at 20:30
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2 Answers 2

up vote 12 down vote accepted

No. Photo editing software cannot recover image detail that is not there in the image originally captured at the scene by your camera. So, enlarging the photo to a very large size will eventually reveal a lack of detail.

Apparent print quality depends a lot on the combination of print size and viewing distance. If you take your photo, print it A2-size and view it from 10m, it will look good. If you walk up to it and view it from 0.2m, it will look worse. No matter what the resolution of the photo, pretty much.

To state this again differently, printing the photo larger will always generate a worse looking photo, unless you also increase the viewing distance.

For standard viewing distances, around an arm's length perhaps, many people find around 300dpi sufficient. Meaning, if the image is 1" x 1", it needs to be 300 pixels per side. If you double the distance, you can halve the number of dpi you need. If you double the image size, you will need double the number of pixels per side for similar quality.

The camera I use most produces images at 4288*2844. At 300dpi, I can produce a print as large as 14" * 9.5" before I start to notice falloff in quality at normal viewing distances (that is, 4288 / 300 = 14.293333... which I rounded to 14 inches).

There are image editing plugins (for Photoshop for example) that help you resize a photo with good subjective quality by inventing image detail that really wasn't in the original photograph, but looks believable, and doing things like Anti-Aliasing to reduce the incongruous appearance of the magnified pixels. Alien Skin Blow Up 3 is an example, but I have never used it.

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As James Youngman points out, it depends on the viewing distance. It also depends on the printer resolution - this is somewhat subjective, but I would imagine you'd want to print between 200-300dpi in most cases.

If you assume a 300dpi print resolution, then simply divide the pixel resolution of the height and width of your image by 300 to get the number of inches you can print.

       Resolution      @300dpi     @200dpi
 6MP    3000 x 2000     10x6"       15x10"
 8MP    3500 x 2300     12x8"       17x12"
10MP    3900 x 2600     13x9"       19x13"
12MP    4200 x 2800     14x9"       21x14"
14MP    4600 x 3100     15x10"      23x15"
16MP    4900 x 3300     16x11"      24x16"
18MP    5200 x 3500     17x12"      26x17"

Here is how to calculate this yourself:

To estimate the pixel dimensions for a number of megapixels, assuming a 3:2 aspect ratio, divide the megapixels by 6, take the square root, then multiply that result by 3 for your width, and by 2 for your height. For example, a 14MP camera. Divide 14 million by 6, which equals 2.3 million. Take square root of that, which equals about 1500. Multiply 1500 by 2 and by 3 to get your dimensions (3000 x 4500).

Now divide 3000 and 4500 by the dpi (for example 300dpi to arrive at a print size of 10" by 15")

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