Apr 01

SPIE: Deconvolution allows Recovery of Full Resolution in Light Field Images

Figure 1. Restoration of a blurred image (simulated data) through deconvolution associated with a plenoptic wavefront sensor. Top left: Original object. Top right: Degraded (blurred) image. Bottom left: Plenoptic acquisition. Bottom right: Restored image. This simulation shows that it is possible to recover an image (obtained with a 512×512-pixel sensor) with only 32 × 32 microlenses. (Image: Rodriguez-Ramos et al., 2015) One of the most limiting hardware factors in light field photography is the loss of image resolution by use of microlens arrays: In Lytro’s light field cameras, the effective image resolution is a factor of 10 below the sensor resolution (i.e. 4 Megapixel images from a 40 Megaray sensor in the Lytro Illum). Raytrix, on the other hand, has managed to achieve up to 25% of sensor resolution using multi-focus plenoptic arrays.

In a recent article on SPIE.org, the Society for Optics and Photonics Technology, researchers José Manuel Rodriguez-Ramos and colleagues discuss a new deconvolution approach which allows recovery of full image resolution from a raw light field picture. Continue reading

Mar 16

Exclusive: Lytro Patents Hybrid Camera for Conventional and Light Field Photography

Fig. 4 from the patent application depicts an architecture for a light field camera suitable for mobile applications, wherein the MLA can be optically disabled to enable higher resolution 2D image capture. (modified after Bhat et al., 2014) The US Patent and Trademark Office has just released a patent application by Lytro titled “Light field image capture device having 2D image capture mode”. The application was filed September 8 2014 by nine (then-) Lytro employees, and describes a dual-mode light field camera that can switch between two modes, allowing either light field imaging or traditional high-resolution 2D imaging:

Abstract: A dual-mode light field camera or plenoptic camera is enabled to perform both 3D light field imaging and conventional high-resolution 2D imaging, depending on the selected mode. In particular, an active system is provided that enables the microlenses to be optically or effectively turned on or turned off, allowing the camera to selectively operate as a 2D imaging camera or a 3D light field camera.

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Aug 05

Samsung Patents Modified Light Field Sensor with Monochrome Sub-Images

Fig. 6 from Samsung's patent application shows three exemplary colour-filtered light rays passing through microlenses to create monochrome sub-images (Fig. modified from Lee et al., 2014). In order to record colour images, camera sensors typically use a colour filter array consisting of red, green, and blue filters on top of the light-intensity sensing sub-pixels. After recording each sub-pixel’s light intensity, the so-called “demosaic” process combines four monochrome sub-pixels (2x red, 2x green, 1x blue) into a single pixel containing RGB colour information.
In microlens-based light field cameras, this “demosaic” job may result in a blur effect around the boundaries of objects in the final image.
Image Sensors World found a patent application by Samsung which can solve this blur-problem: In the patent application entitled “Photographing device and photographing method for taking picture by using a plurality of microlenses”, authors Tae-Hee Lee et al. propose moving the colour filter in front of the microlenses (instead of having them behind the microlenses), creating single-colour sub-images. Continue reading

Jul 15

Visera Patents Integrated Light Field Sensor Manufacturing Process

Fig. 3 from the patent application shows a schematic of a light field camera including the proposed single-piece light field sensor (picture modified from Wang et al., 2014) Light field technology is making its way into the mainstream, but the production and assembly of some of its components has not quite reached an efficient scale of mass production.
A typical light field sensor consists of an ordinary image sensor and a microlens array (MLA) or printed mask.
In the assembly of light field sensors, one of the most vital processes is the precise adjustment of the MLA‘s position on the sensor. This adjustment is required for every individual sensor and can thus take up a long time. Since the MLA is usually positioned using screws or springs, physical impact on the light field camera may displace the light field sensor’s layers.

With patent application US 20140183334 A1 “Image sensor for light field device and manufacturing method thereof“, recently discovered by Image Sensors World, Visera Technologies is aiming for an integrated manufacturing method for light field sensors: Authors Wei-Ko Wang and colleagues propose a system where two layers of microlenses (and an intermediate space layer) are formed directly on the image sensor using semiconductor processes. Continue reading

Jul 01

Sony Patents Light Field Sensor with Full-Resolution 3D Stereo Output

With today’s light field sensors, extracting 3D stereo images from light field recordings typically results in a lowered effective image resolution – but that limitation may soon be history: Sony has developed a novel sensor design with overlapping pixels in two layers, that will allow 3D output without the typical decrease in image resolution. In Sony’s recently granted US Patent, Nr. US20140071244, author Isao Hirota introduces a dual level microlens array setup in combination with a sensor that consists of two layers of light sensitive pixel grids – front-facing and back-facing grids that are rotated at, for example, 45 degrees.
The described configuration allows different neighbouring pixels to share the same information from a single microlens while being allocated to either the left or right stereo views, resulting in higher-resolution 3D stereo output from a single-lens, single-sensor device (i.e. a “monocular 3D stereo camera”).

Fig. 8 from the patent application shows an example setup which uses both a multilens array (34) as well as an additional on-chip lens array (OCL, 35) and color filter array (33) to create a stereo light field image. Fig. 18 from the patent application is a diagram illustrating a CMOS image sensor in which pixels are arranged in a matrix of 2x2 and, for the second layer of pixels, rotated by 45 degrees for multiple perspectives output in the Bayer arrangement.
Fig. 19 from the patent application illustrates how the setup in Fig. 18 allows for nine perspective images (incl. 6 actual parallax images and 3 interpolated ones), making the setup suitable for a monocular 3D stereo camera. Fig. 27 provides examples of electric potential distribution of the light receiving face (back face) in a typical square (A) and triangular (B) pixel, showing that the microlenses can be circular, ellipsoidal or polygonal shapes to improve the lenses' extinction ratios.

Patent abstract: Continue reading