Single-Pixel Camera Is Developed

Researchers from the Optics Research Group at Universitat Jaume I have developed a new tool for the field of scientific imaging, a sensor of just one pixel can record high-quality images and distribute them securely.

In 2009, Willard S. Boyle and George E. Smith received the Nobel Prize in Physics for having successfully captured images with a digital sensor. The key to their work was a procedure that recorded the electrical signals generated via the photoelectric effect in a large number of points, or pixels, in a short period of time. The CCD sensor in a photo camera acts as the human-eye retinal mosaic. Since their invention, the use of the digital format for recording images has revolutionized various fields, photography amongst them, because it facilitates image processing and distribution.

This sequence shows the difference between an image obtained with a wrong encryption key and an unencrypted version.

Nowadays, digital cameras with CCD sensors that have millions of pixels are common. As the dimension of sensors is always the same (typically 24.7 mm2), one may logically think that the higher the number of pixels, the better the image quality will be. However, this idea is not quite right as there are other factors involved, such as the quality of the lens. Conversely, more memory is needed for storing these images (the size of an image created with a 6-megapixel camera is about 2 MB).

In recent years, the world of image technologies has become a booming scientific field, mainly because of biomedical applications. Holographic microscopes, light-operated scissors, laser scalpels, and so on, have enabled the design of minimally invasive diagnosis and surgical techniques. In this context, one amazing possibility that researchers recently have demonstrated is that of capturing high-quality digital images with a sensor using just a single pixel. This technique, dubbed by scientists as ‘ghost imaging,’ is based on the sequential recording of the light intensity transmitted or reflected by an object illuminated by a sequence of noisy light beams. This noisy light is what we observe, for example, when we illuminate a piece of paper using a laser pointer.

Researchers at the Universitat Jaume I Optics Research Group in Castelló, Spain.

The Universitat Jaume I researchers successfully captured 2-D object images (such as the university’s logo or the face of one of the maids of honor from the famous Las Meninas painting as reinterpreted by Picasso in 1957) using this amazing single-pixel camera. The key for the success lies in the use of a small 1-in. LCD screen, similar to that used in video projectors or those we have at home, but in miniature. Its properties or features can be modified using a computer in order to generate the necessary light beams.

Furthermore, the researchers demonstrated, for the first time and on a worldwide scale, the possibility of adapting the technique in such a way that it allows an image to be securely sent to a set of authorized users using a public distribution channel, such as the Internet. The information transmitted is a simple numerical sequence that allows the image to be retrieved, but only if one knows the hidden codes enabling the generation of the noise patterns with which the pubic access information has been created.

The first results of this study, which is still under way, were published in the first July issue of Optics Letters; a month later, Nature Photonics, included a review of it in its September issue.

The technology applied to the single-pixel camera had not yet been used for image encryption, but it is being studied now by several research groups – including the Universitat Jaume I’s optics unit – to obtain images of biological tissues which, because of their unusual transparency or their location in the more internal parts of the body, are difficult to view using pixelated devices such as those of today’s digital cameras. Furthermore, the researchers point out that using this technique for image encryption will improve safety in image transmission, enhance product authentication, or simply hide information from undesired people, thus making it a highly efficient tool against data phishing.

The Optical Research Group at Universitat Jaume I is composed of several investigators under the coordination of Prof. Jesús Lancis. It conducts its activity within the Department of Physics and the recently created Institute for New Image Technologies at the university. In addition to image technologies, the group is participating in a national project on ultrashort and ultra-intense laser pulses, which is financed by the Consolider Ingenio program of the Spanish Ministry of Science and Innovation and the Seventh Framework Programme of the European Union. The project aims to establish this technology in Spain through the Pulsed Laser Centre in Salamanca.

For more information, visit: www.uji.es/UK/basic