Enlargement guaranteed! or not...

July 5, 2006 6:25 PM

How much can I enlarge a digital photo?

I have a photograph I took with my oldish digital camera (2 megapixels). How much can I realistically enlarge it before it starts to look bad? I don't mean doing it myself, necessarily, but I'd love to be able to get this picture up to poster size. Is there any way to do so (ie could a pro photo shop use some sort of projection scheme, or anything like that)?

posted by synecdoche to technology (20 comments total)

2 megapixels is about 1600 x 1200? I find my photos look OK printed at 200 dpi, so that's 6" x 8". Not exactly poster size. You could use Photoshop to enlarge it (Bicubic Sharper) but it won't look right up close. There are speciality enlarging programs too (fractal something or another) but I don't have any experience with them.
posted by Nelson at 6:29 PM on July 5, 2006

I print four-megapixels at 12x18, and they look good. Any larger and they don't. So I don't think you can reliably get a 2-mp photo up to poster size.
posted by raf at 6:33 PM on July 5, 2006

Nelson's basically right. I think the program is called Genuine Fractals. (I, too, have no experience with it, though.)

Obviously, nothing's going to work perfectly, since you only have a finite amount of data. But some programs are better at interpolating than others.

Photoshop will do it (if you have a copy). There's a way (I'm on a Linux machine at the moment) to change the type of interpolation it uses, I think the default is speed-optimized, but there's also a quality-optimized one. I don't know if there's a big difference.

I recall reading somewhere (no idea how accurate this actually is) that repeatedly scaling up slightly produced better results than doing one single enlargement. In other words, increase to 110% of the original size over and over. Again, I've never tried this, but I've read of people swearing by it. (Obviously, it's more time-consuming.)

Also, you don't need great quality if you're doing a poster, unless people are going to be staring at it up-close. I've never looked at a poster from closer than a couple of feet, so if it's a bit pixelated up close, I'd be none the wiser.
posted by fogster at 6:36 PM on July 5, 2006

You have to remember that two thirds of the data in your photo is made up to begin with due to the way digital camera sensors work. There's just not the data there to go more than about, oh, 8x10 or so without looking like hell.
posted by kindall at 7:21 PM on July 5, 2006

The problem is that you only have samples for 2 megapixels worth of information. If you enlarge that it's just going to look blurry and/or blocky. There is no magic or voodoo that can magically recreate that missing detail out of nothing. It's going to look like absolute poo at poster size, and there's nothing in the world that's going to change that short of re-taking the image and capturing all the lost detail. You can fiddle around with bicubic resizing until the cows come home but at the end of the day you have to cope with facts. It doesn't work like Hollywood would have you believe where you can just zoom in indefinitely. That would violate many laws of information theory.
posted by Rhomboid at 7:26 PM on July 5, 2006

I'll second what everyone else has said - your photo has a fixed amount of information in it, two megabytes worth of ones and zeroes - after you enlarge a certain amount you're either making the individual pixels that make up the image bigger or you're asking Photoshop (or whichever program you're using) to make up image information on its own.

Assuming Nelson's 1600 x 1200 size, you'd get high-quality results at about 4 x 6 (300 dpi) , OK-quality at 8 x 10 (150 dpi), and something that would be best viewed at a about three feet distance or more at 16 x 22 (72 dpi). You'll be able to see the individual pixels at that last size.

The size you're asking about works out to about 100 dpi, which can look OK depending on the quality of the printer and paper you use. Not great, but certainly OK, depending on how much of a perfectionist you are.
posted by lekvar at 7:34 PM on July 5, 2006

This probably isn't suitable for your use, but image analogies can be used to enlarge images with less blurryness (although they have their own problems). If you want to try it, there's a sample implementation, but its a) slow, and b) has memory allocation issues.
posted by devilsbrigade at 7:51 PM on July 5, 2006

I would suggest getting the best print possible done at the size you have now (say 4x6-ish) and get that scanned to as big a size as you want. It may look better than scaling the original file up 10,000 percent.
posted by eatcake at 8:00 PM on July 5, 2006

Consider your computer's desktop wallpaper. If you have a 19" LCD, you're running at a resolution 1280x1024 on a screen that is 15"x12". Why would it look hideous when it was printed out instead?
posted by smackfu at 8:05 PM on July 5, 2006

A friend just wrote a blog entry on this very topic; it was so enlightening that I pass it along without further comment.
posted by ikkyu2 at 8:28 PM on July 5, 2006

smackfu: because DPI for print usage is a lot higher than 'DPI' for LCDs.
posted by devilsbrigade at 8:31 PM on July 5, 2006

smackfu-
Monitor resolutions are usually about 72 dpi (dots per inch). Printing resolutions are much, much higher. I work for a printer as a prepress tech and production artist. I never let artwork below 300 dpi hit the press (a 5-color Heidelberg)without making a stink about it beacuse the quality is visibly low. I also babysit a Xerox DucuColor (a high-end laser printer) and I do my best to make sure that nothing below 150 dpi goes to it.

If you look at your desktop wallpaper, you should be able to see the individual pixels without too much strain, especially if you look at an area with any kind of real contrast. The pixels on your desktop also won't appear to be perfect little squares due to the way monitors are manufactured, but the individual pixels will form little squares on the image, due to the way the image data is interprested and printed.
posted by lekvar at 8:34 PM on July 5, 2006

2 MP is not going to support large blow ups. However, the "old" rules for how much blow up an image can suffer and still look good don't really apply any more. Smart interpolation can allow significantly larger blow ups than may people realize today (As an example, I have a camera that is supposedly "incapable" of producing anything nice beyond about 8x12". I've made 20x30" prints that are absolutely stunning, so that "rule" is absolute nonsense). An 8x10 will look fine from your camera, for some definition of fine, as long as the printer is doing decent image interpolation. Even bigger would look acceptable if you let the viewing distance be very large (meaning, bill-boards are blurry as hell by some standards, but they look reasonably sharp when seen from your car at 100 yards).

Some measurebators will tell you that your camera can't even do a good 4x6. They are full of it (my sister has a picture hanging on her wall from a 2MP Nikon that is about 12x18" and it looks fine). Others would happily blow those up to 20x30" and not find the jaggies that resulted as objectionable. There are no hard and fast answers here.

But for casual snapshooter use, 4x6 will look good, and 8x10 acceptable, much beyond that and you will probably start to notice the lack of res, but it still might be completely acceptable to you up to about 12x18" (depending upon how picky you are). Any problem in the image (under or over-exposed, blurry, etc.) is going to become much more obvious with anything bigger than 4x6 at that res, though, so you are going to want to aim for as technically perfect an image as you can manage if you want bigger than that.

If your thinking magazine covers or murals with this camera, fuggedaboutit.
posted by teece at 8:37 PM on July 5, 2006

I'm surprised no mefites have yet suggested the cool tool with the awful name: rasterbator!

There is an online service, and a windows app, as well as a gallery showing some results.
posted by misterbrandt at 8:39 PM on July 5, 2006

misterbrandt: that's not really applicable here... the problem isn't with printing, its with the quality drop when you enlarge an image beyond the data that is there.
posted by devilsbrigade at 10:23 PM on July 5, 2006

Forget about rastorbator...how about vectors? Depending on what your image is, it may look cool as a poster if you use software like Inkscape to turn your image into scalable vectors. While losing gradients and the feel of being a photo, you can scale the resulting image to any size you want - and this works particularly well on faces and images with high contrast and shadows.
posted by Jimbob at 10:43 PM on July 5, 2006

I would second rastorbation. I have one wall of my room covered in Che Guevara thanks to that mighty tool...
posted by gergtreble at 12:23 AM on July 6, 2006

Thanks. The replies are about what I expected. I've used Rasterbator before (indeed, I have a giant Blondie from The Good, The Bad, and the Ugly on one of my walls) but I don't think this image looks quite as nice with that much distortion.
posted by synecdoche at 12:59 AM on July 6, 2006

You could take a look at PhotoZoom and PhotoZoom Professional, from BenVista, which use a patented algorithm (S-spline) to enlarge digital images. In my experience, it works much better than bicubic interpolation.
posted by brianogilvie at 10:20 AM on July 7, 2006

P.S. You can see some examples of S-spline interpolation on BenVista's website. I am not connected to the company, except as a happy customer.
posted by brianogilvie at 10:28 AM on July 7, 2006