EDNE October 2012 - (Page 49)

HDR in this case is the heavy processing required to convert the checkerboard pattern to a normal linear Bayer pattern. This reconstruction requires complex interpolation because, for example, in highlight regions of an HDR image, half of the pixels are missing (clipped). An algorithm must estimate these missing values. While such interpolation can occur with remarkable effectiveness, some impact on effective resolution inevitably remains. However, this tradeoff is rather well controlled, since the sensor only needs to employ the dual-exposure mode when the scene demands it; the A3372 reverts to non-HDR mode when it’s possible to capture the scene via the standard 12-bit single-exposure model. A very different HDR method is the so-called “companding” technique employed by sensors such as Aptina’s MT9M034 and AR0330, along with alternatives from other vendors. These sensors use line buffers to accumulate multiple exposures (up to four, in some cases) line-by-line. The output pixels retain a 12-bit depth, set by the ADC precision, but those 12 bits encompass up to 20 (or more) effective bits of linear intensity data. Companding is conceptually similar to the way that gamma correction encodes two bits of additional data in a colour space such as sRGB. Inverting this non-linear data structure enables derivation of an HDR Bayer-pattern image. This method produces the highest dynamic ranges; one vendor claims 160 dB. But it again comes with associated costs. First, the data inversion relies on a very accurate and stable knowledge of where the various exposures begin and finish. In practice, imperfections lead to noise at specific intensity levels that can be hard to eliminate. Second, the sequential exposures in time create motion artifacts. These can be suppressed but are difficult to remove. Standard tech- es a multi-frame HDR result. www.edn-europe.com OCTOBER 2012 | EDN EuropE 49 http://www.digikey.com/europe http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE October 2012

Cover
Contents
International Rectifier
Microchip
RS Components
Masthead
Microchip
EDN Comment
Pulse
Analog Devices
Farnell
Baker's best
Omicron
Test & Measurement World
Agilent Technologies
Maxim Integrated Products
Maxim Integrated Products
Digi-Key
Mixed-signal SOC verification using analog behavioral models
Messe München
Bergquist
The future of connected-device security
Silicon Laboratories
Digi-Key
Coilcraft
Messe München
Image sensors evolve to meet emerging embedded vision needs
Digi-Key
Chip Expo
National Instruments
Supply chain
Introducing software-designed instrumentation to test-and-measurement
Digi-Key
Mechatronics in design
Design ideas
Product Roundup
Tales from the cube

EDNE October 2012