Wavy Lenses Extend Depth of Field in Digital Imaging

genegeek writes "On Feb 25 CDM Optics was awarded a patent for a new digital imaging system utilizing "Wavefront Coding" that produces images with 10-fold the depth of field of conventional lenses. The image itself is blurred until processed. Image examples are here."

Comments

very cool

[Anonymous Coward]

Ah yes, I know this system well. I did my master's research in extended depth-of-field optics and came across this research which pretty much blew away what I was working on.

Here's a bit of background: in photography or laser scanning (point-by-point photography, basically), you always have a trade-off between depth-of-field and aperture size (as any photographer knows). Bigger aperture means shallow depth-of-field. However, a smaller aperture means lots of wasted light (imagine closing the aperture in your camera), and this means longer exposure times, and more importantly more NOISE in your images. This is true for digital, film, or photodetector.

So the "holy grail" is to keep the aperture open but still have high depth-of-field. This system depends on changing the phase of the light, instead of the amplitude (which is what you do when you stop down a lens to a smaller aperture). That way, no light energy is blocked and wasted.

Since the phase is changed, the resulting image on the CCD or film is fuzzy and has to be "decoded". You can think of it as "encoding" the wavefront in a special way that preserves the depth of field, capturing the image, and then "decoding" it into a sharp picture. It is really amazing. I hope it shows up in consumer cameras someday, it could completely change consumer photography since most "snapshot photographers" don't care about depth of field or all that stuff. It will also be great for medical and industrial imaging.

My system was sort of a hybrid between shading the aperture (instead of a sudden stopping of light, it gradually goes to black at the edge) and phase changes. Lots of people have been working on this problem over the years, but these guys really stripped the problem down to the essence and came up with a highly optimized solution.

Re:Film and digital resolution comparisons

[darkonc]

http://www.robgalbraith.com/bins/content_page.asp? cid=7-4833-4853
and: http://www.luminous-landscape.com/reviews/cameras/ 1ds/1ds-field.shtml

It's just polite to make such links both active and accurate (extraneous spaces in both links -- probably inserted by slashdot because you tried to submit the URLs as plain text).

University site with original papers

[iblink]

Although Colorado University may never forgive me, this address has links to the research papers as well as more images: http://www.colorado.edu/isl/

Re:So

[plover]

Except that weakness turns out to be a strength when dealing with aliasing. The random orientation of the individual grains avoids aliasing issues. Even at a resolution exceeding that of the film grain, a grid of parallel lines (especially parallel or concentric curves) can produce a noticable moire effect. Also, I've found that angled black and white lines can have noticable color artifacts (although I understand there's a new CCD technology that's supposed to overcome this problem.) The randomness of the grain also seems to provide a "softening" effect that I personally find more pleasing than the regularity of a matrix of pixels.

Don't get me wrong: I *love* my Canon PowerShot G2 (4MP). I've been extremely pleased with the results in a 4x6 format. I've blown up some as large as 8x10 (had them professionally printed and developed) and find that the quality is almost as good as prints made from 100 ISO 35mm film. Having "during the shot" color balancing also makes it much easier to get useable prints without serious headaches. And it's certainly more conveinent to me to have the images digitally available, too.

I also find that without my old-school mental block of "don't waste film" is gone, and that I now take many more shots than I used to. It leads to a bigger choice of shots to choose from, so I now get better final prints. Yes, I know I wasn't supposed to worry about "wasting film" before, but those old habits are very hard to break.