EDN on Image Sensors

EDN published an article on consumer image sensors problems:

"For a given sensor size—and hence price range—increasing the pixel count means decreasing the active area of the photodiode, and hence lowering the sensitivity and/or the signal-to-noise ratio. Already in the 6-megapixel range, sensitivity has been reduced enough to seriously compromise image quality at low light levels.

One possible solution comes from Toshiba, which is working on a way to get more light to the active area. Today the individual microlenses that are bonded onto the surface of the image-sensor array are circular—so the lens doesn't collect light from the whole rectangular area of the pixel cell, only from a circular area that fits inside the rectangle. Toshiba researchers are working on a rectangular microlens that would cover the entire pixel area, substantially increasing light-gathering efficiency."

Well, Micron has these high-quality microlens for years. Toshiba is catching up here.

"Toshiba is also working on the system-architecture problem. In many cell-phone handset designs today, even the pixel-level post-processing to remove noise and bias from the raw CMOS sensor data is done on the handset's baseband or applications processor. But, according to Toshiba vice president Andrew Burt, while that solution is attractive to platform developers for cost reasons, it is losing its appeal with handset manufacturers, who find that the design team that created the sensor should remain in control of the pixel-level processing. This is tending not only to put the pixel-level signal-processing hardware back on the sensor die, but also to enlarge the definition of what needs to happen at the pixel level. "As resolutions approach 5 to 8 megapixels, we see image-processing applications migrating onto the pixel processor," Burt said."

I think this is another way to say that sensor's raw data is so bad that it's a shame to show it to anybody without at least basic fixes on the sensor itself.

Then EDN says about video camera sensor problems:

"At least one insider sees video cameras heading down the same road. Cameras are moving to true HD: 1080-line, progressive-scan imaging. That means the consumer is going to be looking at the output of a handheld camera on an HD screen in high resolution. The consumer is not going to be happy.

Part of the problem is refresh rate. "Hollywood can make movies at 24 frames per second," observes Didier LeGall, executive vice president at Ambarella. "But they have professional cinematographers and specifications written right into the script about how fast a pan or zoom will be, how a camera will track, how fast the hero will run across the scene, and so on.

A novice recording HD sequences with a handheld camera, swinging it around, zooming in and out, is going to create flicker and motion artifacts at anything like a 24 fps refresh rate. That is one of the reasons the industry is moving rapidly toward 120 Hz."