Computing

Pushing Pixels

Kodak brings digital cameras into the 50-megapixel range.

Last week, Kodak launched the first ever 50-megapixel camera sensor. While such high resolution goes beyond the needs of most consumers, for professional photographers the new sensor will enable photographs to be taken at an unprecedented level of detail.

Fifty megapixels: Kodak’s new 50-million-pixel camera sensor manages to squeeze more pixels onto an array while simultaneously increasing the speed and reducing the power consumption of the device.

For example, in a picture taken of a field one-and-a-half miles across, the sensor would make it possible for a viewer to detect an object measuring just one foot across.

This sort of resolution is only really essential for and targeted at high-end professional photography, in which high-quality images often need to be blown up large. But it could also be useful for some other applications, such as aerial photography as used for services like Google Earth. “The ability to have more pixels lets the plane fly higher, so you don’t need as many pictures,” says Mike DeLuca, marketing manager for Kodak’s Image Sensor Solutions, based in Rochester, NY.

The sensor, which produces an array of 8,176-by-6,132 pixels, further closes the gap between traditional film and digital photography. “We’re really close to how film was operated,” DeLuca says. “It’s very close.” Now, he says, it’s just a matter of the photographer’s personal preference.

Normally, the smaller you make a pixel, the poorer the quality, says Albert Theuwissen, a digital-imaging expert and founder of Harvest Imaging, based in Bree, Belgium. “That is true for consumer as well as professional devices.” DeLuca claims that in the case of Kodak’s breakout sensor, new pigments actually increase the color quality rendered by the sensor, while other mechanisms enable the pixels to be just as sensitive as larger ones–and yet they’re processed faster than in previous designs. What’s more, he claims that the new sensor uses less power than its predecessors. “Every solution or step that makes the sensor faster and less power hungry is a step forward,” says Theuwissen.

Kodak already has a sensor on the market with a resolution of 39 million pixels. But to further increase the resolution, the company had to not only reduce the size of each pixel from 6.8 microns to 6 microns, but also radically change the way that these charged coupled device (CCD) sensors work, says DeLuca.

“It’s relatively straightforward to make the pixels smaller,” he says. But because these devices comprise much more than just light-detecting elements, DeLuca says, they can suffer drops in performance if everything inside them is not shrunken along with the pixels.

“Each pixel has multiple structures,” he says. Some are designed to pass a charge from one pixel to the next, to enable the image to be read off the device. Other structures ensure that any excess charge produced by bright lighting conditions doesn’t spill out into neighboring pixels.

Another challenge is to maintain the dynamic range of the sensor–that is, its ability to detect light and dark simultaneously. In the sensor, this is basically a signal-to-noise issue, says DeLuca. “When you make the pixel smaller, there is less signal you are able to capture, because physically there is less ability to store electrons in that pixel. If we don’t do anything else, what we end up with is a smaller signal with the same noise profile.” To counteract this, Kodak has had to improve the amplifier at the output of the device, which reduces the noise.

Also, by increasing the number of pixels, it becomes more challenging to access the information once it has been detected. “Fifty million pixels is a lot of data,” says DeLuca, and a photographer needs to be able to read it off the sensor in a reasonable amount of time.

Until now, Kodak has used a process that involved dumping the information from one row of pixels onto the next and shifting the information along the row, reading it off at the edge, one pixel at a time. This is a relatively slow process, normally carried out two rows at a time. So to cope with the additional amount of data, the new sensor comes with four output channels so that four times the amount of data can be read at once. This enables the sensor to increase the rate at which images can be captured from 0.9 to 1.0 frames a second, even though more information is being captured. And yet this also allows the clock cycle at which the data is read off to be reduced for each output, which further improves the signal-to-noise ratio.

Power savings are achieved by the way that the sensor is reset before each picture is taken. This is carried out just before a shot is taken to ensure that there is no residual charge or electrical noise in the pixels that could reduce the quality of the new image. In previous sensors, Kodak has simply read out each of the pixels row by row, as if collecting the data for a picture, but then it dumped the information instead of storing it. “What we’ve included now is a new structure in the pixel which allows all the pixels in the array to be cleared out in a single clock pulse,” says DeLuca. So instead of having to flush the entire sensor row by row, you flush the entire array in one go, he says.

This dramatically improves the “click to capture” time–the delay between pressing the shutter down and the sensor capturing the image. “Instead of being milliseconds, it takes microseconds,” says DeLuca. And in addition to saving time, it also reduces the power that is required to perform a reset.

This technology doesn’t come cheap. The sensor alone will cost at least $3,500. But that doesn’t appear to have put off one camera manufacturer. Hasselblad has announced plans to launch a new camera featuring the sensor in the coming months. Nor is 50 megapixels going to remain on the cutting edge for long. Just this week, a few days after Kodak’s announcement, another digital-imaging firm, DALSA, based in Waterloo, Canada, announced that it has developed a 60-megapixel sensor.

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