Digital Micromirror Device Camera Research Articles

Digital micromirror device camera with per-pixel coded exposure for high dynamic range imaging.

In this paper, we overcome the limited dynamic range of the conventional digital camera, and propose a method of realizing high dynamic range imaging (HDRI) from a novel programmable imaging system called a digital micromirror device (DMD) camera. The unique feature of the proposed new method is that the spatial and temporal information of incident light in our DMD camera can be flexibly modulated, and it enables the camera pixels always to have reasonable exposure intensity by DMD pixel-level modulation. More importantly, it allows different light intensity control algorithms used in our programmable imaging system to achieve HDRI. We implement the optical system prototype, analyze the theory of per-pixel coded exposure for HDRI, and put forward an adaptive light intensity control algorithm to effectively modulate the different light intensity to recover high dynamic range images. Via experiments, we demonstrate the effectiveness of our method and implement the HDRI on different objects.

Per-Pixel Coded Exposure for High-Speed and High-Resolution Imaging Using a Digital Micromirror Device Camera.

High-speed photography is an important tool for studying rapid physical phenomena. However, low-frame-rate CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) camera cannot effectively capture the rapid phenomena with high-speed and high-resolution. In this paper, we incorporate the hardware restrictions of existing image sensors, design the sampling functions, and implement a hardware prototype with a digital micromirror device (DMD) camera in which spatial and temporal information can be flexibly modulated. Combined with the optical model of DMD camera, we theoretically analyze the per-pixel coded exposure and propose a three-element median quicksort method to increase the temporal resolution of the imaging system. Theoretically, this approach can rapidly increase the temporal resolution several, or even hundreds, of times without increasing bandwidth requirements of the camera. We demonstrate the effectiveness of our method via extensive examples and achieve 100 fps (frames per second) gain in temporal resolution by using a 25 fps camera.

Design of a high-numerical-aperture digital micromirror device camera with high dynamic range.

A high-NA imaging system with high dynamic range is presented based on a digital micromirror device (DMD). The DMD camera consists of an objective imaging system and a relay imaging system, connected by a DMD chip. With the introduction of a total internal reflection prism system, the objective imaging system is designed with a working F/# of 1.97, breaking through the F/2.45 limitation of conventional DMD projection lenses. As for the relay imaging system, an off-axis design that could correct off-axis aberrations of the tilt relay imaging system is developed. This structure has the advantage of increasing the NA of the imaging system while maintaining a compact size. Investigation revealed that the dynamic range of a DMD camera could be greatly increased, by 2.41 times. We built one prototype DMD camera with a working F/# of 1.23, and the field experiments proved the validity and reliability our work.

Removal of parasitic image due to metal specularity based on digital micromirror device camera

Visual inspection for a highly reflective surface is commonly faced with a serious limitation, which is that useful information on geometric construction and textural defects is covered by a parasitic image due to specular highlights. In order to solve the problem, we propose an effective method for removing the parasitic image. Specifically, a digital micromirror device (DMD) camera for programmable imaging is first described. The strength of the optical system is to process scene ray before image formation. Based on the DMD camera, an iterative algorithm of modulated region selection, precise region mapping, and multimodulation provides removal of the parasitic image and reconstruction of a correction image. Finally, experimental results show the performance of the proposed approach.

DMDカメラを用いたSTEP法による広ダイナミックレンジ映像撮影法

A wide dynamic range image recording technique using a digital micromirror device (DMD) camera with a spatio-temporal exposure pattern (STEP) method is proposed. By incorporating DMD technology, each pixel in the DMD camera can be recorded at a different exposure time. The wide dynamic range images are reconstructed using the spatial and temporal intensity information simultaneously. Preliminary experimental results showed that the DMD camera can record wider dynamic range images with a minimum reduction in resolution.

Single-shot three-dimensional shape measurement method using a digital micromirror device camera by fringe projection

We present a new single-shot 3-D shape measurement method using a digital micromirror device (DMD) camera and fringe projection. In optics of the DMD camera, individual DMD mirrors operate as controllable high-speed shutters for corresponding charge-coupled device (CCD) pixels. Therefore, four phase-shifted images can be recorded within one frame of the CCD camera by integrated phase-shifting methods using correlations. To obtain 3-D information of the object, an easy and accurate phase-to-3-D calibration method is performed. The principle and hardware are presented. The experimental results under dynamic conditions show that 3-D shape information can be analyzed from only a single image.

Intensity range extension method for three-dimensional shape measurement in phase-measuring profilometry using a digital micromirror device camera

Phase-measuring profilometry is an accurate and effective technique for performing three-dimensional (3D) shape and deformation measurements of diffuse objects by fringe projection. However, phase analysis cannot be performed in underexposed or overexposed areas of the detector when an object with wide reflectance is measured. A novel intensity range extension method using a digital micromirror device (DMD) camera is proposed. In the optics of the DMD camera, each pixel of the CCD corresponds exactly to each mirror of the DMD. The phase-shifted fringe patterns with high contrast can be easily captured by programming an inverse intensity pattern that depends on the reflectance of the object. Our method can provide a wider intensity range and higher accuracy for 3D shape measurement than other conventional methods in both underexposed and overexposed areas. The measurements of a replica of a metallic art object and a flat plane are analyzed experimentally to verify the effectiveness of our method. In the experiment, the percentage of invalid points due to underexposure and overexposure can be reduced from 20% to 1%.

OS1-2-4 One-shot Shape and Deformation Measurement Method Using DMD Camera

Noncontacting shape measurement for 3-D objects is important in automated manufacturing, component quality control, reverse engineering, etc. Phase-shifting method effectively attains high resolution and high accuracy in analyzing phase information on a projected grating. This technique, however, is difficult to be applied to dynamic condition since usually it requires several images. We developed a digital micromirror device (DMD) camera for phase analysis. In this paper, an one-shot shape and deformation measurement method using a DMD camera is proposed. The DMD camera consists of a DMD, a CCD, and two imaging lenses. In optics of the DMD camera, individual DMD mirrors correspond to individual CCD pixels. The DMD on-off binary pattern can be changed more than 6900 times in one second using an accessory light modulator package (ALP) controller board. Individual DMD mirrors operate as controllable high-speed shutters for corresponding CCD pixels. The four phase-shifted images can be recorded within one frame of the CCD camera. Therefore, shape measurement in dynamic condition can be realized without using a high-speed camera. In order to obtain the 3-D information of shape, multiple reference planes are used to calibrate the relationship between phase value and 3D coordinates. The principle and hardware are presented. In an experiment under dynamic condition, 3D shape information can be analyzed from only one captured image.

Development of DMD Reflection-Type CCD Camera for Phase Analysis and Shape Measurement

Phase-shifting method effectively attains high resolution and high accuracy in analyzing phase information on a projected grating. It is difficult to apply dynamically, however, because it usually requires several images. We developed a camera based on digital micromirror device (DMD) technology for high-speed phase analysis and shape measurement, called a DMD reflection-type CCD camera or DMD camera. Implementing DMD technology enables accurate control of intensity reaching the imaging detector of a camera. Moiré is used to adjust pixel-to-pixel correspondence highly accuracy. We introduce a controllable high-speed DMD operation board to control DMD mirrors at high-speed, so each DMD mirror operates as a controllable high-speed shutter for the corresponding CCD pixel. In experiments with an application, we conducted DMD integrated phase-shifting method using correlation to analyze phase distributions of projected gratings from images recorded by the DMD camera. We then discuss principles and experimental results under dynamic conditions. This paper is a revised version of one presented at the SPIE International Symposium on Optomechatronic Technologies (ISOT 2005), December 4-7, 2005 at the Sapporo Convention Center, Japan. That paper appears in SPIE Proceedings Vol.6049, 60490I.

Accurate pixel-to-pixel correspondence adjustment in a digital micromirror device camera by using the phase-shifting moiré method

A camera based on the digital micromirror device (DMD) technology has been previously developed. In this optical system, the correspondence of each mirror of the DMD to each pixel of the CCD cannot readily be done since the pixel sizes of the DMD and the CCD are very small. An accurate pixel-to-pixel correspondence adjustment in the DMD camera by means of the phase-shifting moiré method is proposed. To perform high accurate adjustment of the optical system, the phase distribution of a moiré fringe pattern is analyzed when the CCD pixels and the DMD mirrors have a mismatch and/or misalignment with each other. This technique does not need a complicated setting or complex image processing to generate the moiré fringe pattern, and it needs only one captured image. In the adjustment experiment, the proposed method provided very accurate adjustment whose error was less than 1/25 pixel. An experiment of phase analysis to demonstrate the usefulness was performed.

Pixel-to-Pixel Correspondence Adjustment in DMD Camera by Moiré Methodology

DMD (Digital Micro-mirror Device) is a new device, which has hundreds of thousands of micro-mirrors in one chip. We developed a DMD reflection-type CCD camera that we call ‘DMD camera’ previously. In this optical system of the DMD camera, each mirror of the DMD is corresponded to each pixel of the CCD. As a result, each DMD mirror works as a high-speed controllable shutter of the corresponding CCD pixel. However, corresponding each mirror of the DMD to each pixel of the CCD cannot readily be done since the pixel sizes of DMD and CCD are very small. In this paper, a pixel-to-pixel correspondence adjustment method, which can perform accurate adjustment of the DMD camera optical system by moire methodology is proposed. The proposed method is easy and visual by observing the moire pattern. This method enables DMD camera to adjust pixel-to-pixel correspondence less than one pixel accuracy of the CCD. An experiment of phase analysis to demonstrate the improvement of the resolution and accuracy was performed.