Digital Photography

Take My Pixel

Digital cameras come with lots of bells and whistles. But what matters most is picture quality, and it has improved significantly in the newest pixel takers.

Instead of striking unexposed film, light entering a typical digital camera is focused onto a charge-coupled device, or CCD. This semiconductor array, consisting of many tiny picture elements (pixels), converts light energy into electron charge. A microprocessor reads the charge in each pixel as a digital signal and constructs an image of the scene.

CCDs and the human eye do not "see" light the same way, however. Creating authentic images depends on coherent focusing, color correction and proper whiteness. Aspherical lenses, which have nonspherical curvature, are inserted between the usual spherical lenses so light is focused uniformly on all pixels, improving sharpness. Filters in front of pixels ensure that color-processing algorithms can generate lifelike and bright colors. Other algorithms check for biases in the wavelengths of incoming light; these indicate the presence of fluorescent lighting, which gives a green cast, or tungsten (incandescent) lighting, which gives a yellow cast. The algorithms eliminate the tint, which the human brain does automatically, so a scene's true color and whiteness appear the way we expect them to appear.

The latest digicams also minimize practical problems of early models. Optical zooming, achieved by moving the lenses, was limited in order to keep cameras compact; so-called digital zoom extends the range using software processing. And faster digital-image-processing chips have sped up click-to-click time—how quickly the camera can take pictures in succession—to 1.5 seconds or less.

Click-to-capture time—the delay between the moment the shutter button is pushed and the moment the shutter actually opens—has also been reduced to half a second or less, primarily by speeding up autofocus. "In the early days a lot of people took pictures of their shoes," says Gary Hallenbeck, new-business development manager at Eastman Kodak Company; they had pushed the shutter button, figured the shot was taken and lowered the camera before the shutter opened. — Mark Fischetti

DIGITAL CAMERA'S lenses focus light onto a charged-coupled device (CCD). It converts light into electronic charge data sent to a buffer memory. The processor accesses the data, reduces signal noise, corrects color and whiteness, and sends a final digital image to internal memory or to an inserted memory card.

Flash

Infrared beam-

Ambient light rays

Infrared beam-

Ambient light rays

Flash

ASPHERICAL LENS ELEMENTS (right) are inserted among spherical lenses to correct distortion. Spherical lenses have difficulty focusing incoming parallel light rays that strike the lens's outer edges and center into a single convergence point, causing fuzzy edges in a picture (diagrams). In this case, the first group of glass elements funnels rays onto the second group, which moves forward and backward as focusing or zoom requires. The second group narrows light onto the fixed, third group, which directs beams onto the CCD.

> MEGAPIXEL MAX: A so-called four-megapixel camera has a CCD with four million pixels. The higher this resolution, the sharper the photograph. But affordable lens systems cannot resolve light into more than six or eight megapixels, Kodak's Gary Hallenbeck says. So consumer cameras touting 10 or 12 megapixel sensors will not create an overall sharper image. The higher count does help make images clearer when using digital zoom, however.

> THUMBNAIL: The "photograph" in most digital cameras is created in jpeg (Joint Photographic Experts Group) format, a graphic standard used widely on computers and the Internet. What you see on the camera's little liquid-crystal display screen is a "thumbnail"

version of that image. The thumbnail typically contains about 150,000 bytes of data, commonly known as a 150K file.

> FAST FOCUS: To autofocus, many cameras use external CCDs to sense ambient light. The processor first evaluates the charge on the CCDs and triangulates to gauge distance. Then it moves the lenses and repeats the process until the peak charge is found and bypassed (envision the top of a sine curve). The lenses are set at the peak position, the shutter opens, and the processor fine-tunes the focus by sampling the main, imaging-recording CCD. By establishing a rough focus, this approach requires fewer cycles than older models that just used the main CCD, speeding up autofocus.

Internal memory Buffer

Optical zoom GrouP 3

Pixel

Regular lens

Light

Light

Low-dispersion lens

Low-dispersion lens

COLOR FILTER covers each pixel on a CCD so it registers only one color. Most cameras use a Bayer filter pattern, as shown; green is favored because the eye is more sensitive to that wavelength. The processor combines the red-green-blue signals into a full-color image. New, low-dispersion lenses (diagrams) help to reduce color inaccuracies caused by different wavelengths that naturally focus at slightly different points.

Section of original image

Same section at 2X digital zoom

Optical zoom GrouP 3

GrouP 1 Group 2

Group 2 g

Group 2 Aspherical lens

Aspherical lens

Section of original image

Same section at 2X digital zoom

A

(AB)

B

C

(CD)

D

Critical edge rays r

Aspherical lens

Light

Light

Spherical lens

Aspherical lens

Spherical lens

Aspherical lens

DIGITAL ZOOM begins once lenses are fully deployed, which maxes out optical zoom. For 2x digital zoom, the processor crops in to 50 percent of the original image; for 4x zoom, to 25 percent. It then positions known pixels (A, B) in a grid that fills the full frame and interpolates their values to determine colors for intermediate pixels (AB). This estimation decreases image sharpness.

Topic suggested by Yang Zhou and Kurt Becker. Send ideas to [email protected]

REVIEWS

An Institution between Covers

THE 39TH EDITION EXPANDS GRAY'S ORIGINAL TASK BY SHERWIN B. NULAND

GRAY'S ANATOMY: THE ANATOMICAL BASIS OF CLINICAL PRACTICE,

39th edition Edited by Susan Standring and others Elsevier Churchill Livingstone, 2005 ($169)

The eminent mid-20th century British historian of medicine F.N.L. Poynter once said of Gray's Anatomy that "what began as a book has become an institution."

Like all progressive institutions, this one periodically looks itself over, evaluates its development and takes measures to be sure that it has kept up with the times. Keeping up has occasionally required increasing the complexity of its operations, necessarily expanding its bureaucracy, and seeking new and forward-looking leadership. As the institution among medical books, Gray's Anatomy has throughout its history continued to do all these things, with the result that it has only improved with age; it is venerable but not hoary.

With this prologue as background, I am pleased to report that the all-important tradition of improvement with age is most emphatically maintained by the newest edition of Gray's Anatomy, the 39th. The new leadership comes in the accomplished person of Susan Standring, professor of experimental neurobiology at King's College London and incidentally the first female editor in chief. The necessary bureaucracy has been once more expanded to an assemblage of what is by my count a total of almost a score of editors and more than three times that many specialist contributors and reviewers, some of whom are respected holdovers from the excellent 38th edition of 1995. The volume resulting from everyone's labors is, at 11 pounds, now heavy enough for use as a gym weight to build the skeletal muscles it so elegantly describes, from their myoblastic genesis and cellular physiology to their good old-fashioned origins and insertions.

Anyone perusing the last 10 incarnations of this vigorous old warhorse of medical literature will note that a significant change came about with the 35th in 1973, when the visual character of the book began a veritable transformation. Since that time, each edition has incrementally added material covering advances in such fields as molecular biology, imaging, computer-assisted and electron microscopy, embryology and immunohistology to encompass new knowledge and provide didactic clarifications. Henry Gray's original offering of 1858 has taken on the task of providing an overview of the science on which comprehensive understanding of gross anatomy is based in today's biomedical and clinical worlds.

After the publication of the 37th edition in 1989, a formal editorial board was created to provide a supervisory framework for the additions being made by the specialist authors whose contributions were increasing the value of Gray's Anatomy as a source for basic science and clinical applications. When the next edition appeared in 1995, the main changes to be found in it—other than new sections on surface and neonatal anatomy—were organizational, consisting primarily of rearranging the material to make it more accessible and useful. But with the present volume, new and important ground has been bro-ken—or at least more fully and effectively tilled. The authors have increasingly taken on the task of accommodating the new uses to which anatomy is being put in clinical situations, such as minimally invasive surgery, endoscopy, arthrosco-py, microsurgery, and the entire expanding field of imaging, including three-dimensional studies.

In addition to providing many pertinent illustrations, Standring and her au-

EXTENSOR MUSCLES of the left forearm, one of almost 2,000 illustrations from the latest edition of Gray's Anatomy.

thoritative team have taken the major and very practical step of presenting their material by regions rather than by the old method of systems such as the reproductive, the gastrointestinal and the muscular. This is a tremendous advantage for clinicians, because it reflects the way in which they need to see anatomy. And it has at least as worthy a benefit for students, because it will correlate even their earliest first-year learning directly to the real world of bedside medicine. Not only that, but brief comments about common diseases are interspersed in the text as their respective anatomical locations are being discussed. All of this is reflected in a change in the book's subtitle, which on first glance would seem insignificant but actually says a great deal. It has gone from The Anatomical Basis of Medicine and Surgery to The Anatomical Basis of Clinical Practice.

Quite obviously, no single reviewer is competent to judge the reliability of every bit of material to be found in this encyclopedic book. As a general surgeon selectively studying sections with which I have a career's worth of experience and only perusing others, I am much taken with their usefulness and lucid readability, which says a great deal for an anatomy text. At the astonishingly low price of $169 for the print edition and only an extra $30 to have it on CD-ROM and online as well, this may be the best value seen in medical publishing since 1819, when René Laennec's two-volume treatise on auscultation was put on sale at a price of 13 francs, with a stethoscope thrown in for a small additional cost.

One final word. It is customary when reviewing a book that is in all ways as outstanding as this one to introduce a quibble or two, if for no other reason than to show that the volume has been carefully and completely eval-

* Tjjlesel PDF ill flit Orty softirair lhat aliows you 1d iransfcr m tflfcX fil» 1a POF H^ hyper¡ir*«l ¿rd drth wiieddfi ^raphia in wer 50 formais

•Ex)»t1<kMuiinmlias RTF «itfi ndilablc math [MitrosiJlWhrdand Mäflhlyps íompaítlí) • Shsrs ûjm meits on !he » HTML nifli malli « MaihHL w graphies

Vtuw nfiyv I hrifice fl vtfHmin im

foii+tt. ITi-lHrWi

www, mackiehan. com/s a

Are You Missing an Issue?

Order back issues of Scientific American right online.

Simply visit

www.sciam.com/orderissues

to pick up any issues you missed to complete your Scientific American collection.

Newsstand Only Special Editions, which are not part of our regular subscription, are also available for purchase.

With ordering made this easy, you'll never miss an issue!

Limited Availability... Place your order now!

Renewable Energy

Renewable Energy

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook


Post a comment