Software-enhanced optics provides a means for delivering a fully automatic solution for camera phones that enables the consumer to obtain clear images under a wide range of luminance conditions. The basis of the approach is to design the camera module with low F-number optics, typically F/1.75, and restore the depth of field to normal using the extended field depth solution described above. The low F-number optics makes the ultra fast lens solution suitable for both still photography as well as video feeds. The signal processing compensates for loss of contrast and substantially reduces noise in the final image, while preserving edges, fine details and texture. This is possible because the information written to the line buffers necessary to run the algorithms can be reused to provide pixel-averaging data and improve the signal-to-noise ratio of the image by up to 6dB. The effectiveness of this solution can be clearly discerned by comparing the two photographs, taken with identical imagers having 1.75μm pixels, in Figure 9.

Implementation
Software-enhanced optics combines a special lens with a custom algorithm to deliver remarkable quality pictures in a way that is totally transparent to the consumer. However, the camera module designer needs to think ahead to incorporate these image enhancement technologies in a handset, as it cannot be done as an add-on. In principle, all that is required is one custom-designed lens in the optics train that can be manufactured using the existing infrastructure and lens materials. The custom lens can even substitute for an existing lens. Allied with this is the image processing algorithm. The algorithms for these solutions are usually small, taking approximately 100k gates. This is small enough for the algorithm to be embedded in the image pipeline on the CMOS imager, but clearly requires co-operation with the image sensor manufacturer, and the die must then be married to the correct optics.

The alternative placement for the algorithm is as software or firmware running on a dedicated image processor or the phone processor. Again, both of these solutions are very simple from a technical standpoint but require communication outside of the traditional camera module supply chain. Nevertheless, the benefits of these solutions are so compelling that 3Mpixel camera phones with extended field depth are already in production and will be proliferating--together with zoom and ultra fast lens solutions--to higher resolution cameras in 2009.

While software-enhanced optics work to boost the raw performance of highly miniaturized and low-cost camera modules, apart from the zoom solution, they do little to provide features that stoke customer satisfaction with the picture-taking experience. This issue matters little to the camera module designer, but is of very great importance to the original equipment manufacturer. One of the most commonly encountered annoyances from digital camera photographs is red-eye, which explains why red-eye reduction is today implemented on more than 80 percent of digital still cameras. Whether features such as this can be provided on camera phones and how they can be integrated is discussed in Part 4 of this article series.

About the Author
Giles Humpston, Ph.D., serves as Director, Research and Development ofTessera. Dr. Humpston has spent his entire professional career working in the field of semiconductor packaging, initially for military applications and more recently for high volume consumer products. He is a metallurgist by profession and has a doctorate in alloy phase equilibria. Dr. Humpston is a cited inventor on more than 75 patents and has co-authored several text books on metallic joining processes. His work and technical publications have been recognized by five international awards. Dr. Humpston's current interests are packaging of solid state camera modules and product miniaturization through wafer level technologies. He can be reached at: ghumpston@tessera.com

For more on the subject:

Tips and Tricks: The critical nature of cell phone camera packaging
What you need to know about imaging solutions for camera phones
Cameras in handsets evolving from novelty to DSC performance, despite constraints
Image pipeline: Fine-tuning digital camera processing blocks
Get enlightened about camera phone flash units--compare Xenon to high current LEDs