计算摄影综述

随着计算机、传感器等先进技术的发展,一种新的摄影技术——计算摄影逐渐形成。计算摄影是利用计算机软件方法结合现代传感器及现代光学等技术创造出新型摄影设备以及相关应用的综合技术,它突破了传统数码摄影技术难以解决的种种难题,成为摄影技术的又一次新的变革。为加深对计算摄影研究领域的了解,从计算场景、计算光学、计算传感器以及计算处理四个方面介绍了计算摄影研究的热点问题,总结了计算摄影存在的问题及其发展趋势。     

摄影与手工渲染的结合

通过素描,绘画和时尚照片的混合来制作丰富的图像。Alexis West将为我们介绍一些非常有价值的技术。     

Flexible depth of field photography

The range of scene depths that appear focused in an image is known as the depth of field (DOF). Conventional cameras are limited by a fundamental trade-off between depth of field and signal-to-noise ratio (SNR). For a dark scene, the aperture of the lens must be opened up to maintain SNR, which causes the DOF to reduce. Also, today's cameras have DOFs that correspond to a single slab that is perpendicular to the optical axis. In this paper, we present an imaging system that enables one to control the DOF in new and powerful ways. Our approach is to vary the position and/or orientation of the image detector during the integration time of a single photograph. Even when the detector motion is very small (tens of microns), a large range of scene depths (several meters) is captured, both in and out of focus. Our prototype camera uses a micro-actuator to translate the detector along the optical axis during image integration. Using this device, we demonstrate four applications of flexible DOF. First, we describe extended DOF where a large depth range is captured with a very wide aperture (low noise) but with nearly depth-independent defocus blur. Deconvolving a captured image with a single blur kernel gives an image with extended DOF and high SNR. Next, we show the capture of images with discontinuous DOFs. For instance, near and far objects can be imaged with sharpness, while objects in between are severely blurred. Third, we show that our camera can capture images with tilted DOFs (Scheimpflug imaging) without tilting the image detector. Finally, we demonstrate how our camera can be used to realize nonplanar DOFs. We believe flexible DOF imaging can open a new creative dimension in photography and lead to new capabilities in scientific imaging, vision, and graphics.     

Low-cost ground-based digital infra-red photography

The paper describes how many types of inexpensive digital camera can be used to take monochrome and false colour infra-red photographs. The method avoids many of the limitations of infra-red sensitive film and produces excellent results rapidly and at low cost.     

Stereo-based bokeh effects for photography

Bokeh, a sought-after photo rendering style of out-of-focus blur, typically aims at an esthetic quality which is not available to low-end consumer-grade cameras due to the lens design. We present a bokeh simulation method using stereo-vision techniques. We refine a depth map obtained by stereo matching, also using some minor user interaction. Overexposed regions are recovered according to depth information. A depth-aware bokeh effect is then applied with user-adjustable apertures sizes or shapes. We also simulate swirly bokeh, also known as cat-eye effect. Our method mainly aims at the visual quality of the bokeh effect rather than (so far) at time efficiency. Experiments show that our results are natural looking and that they can be comparable to bokeh effects achieved with expensive real-world bokeh-capable camera systems.     

Automatic exposure algorithms for digital photography

Multimedia Tools and Applications - In this paper we deal with the problem of calculating Automatic Exposure (AE) in digital cameras. The main problem that often occurs when taking pictures is...     

Interactive motion photography from a single image

In this paper, we present an interactive and computational method of creating a motion photograph from a single image. Inspired by cartoon arts, a motion photograph is a still image in which moving objects are depicted as informative and motion-evocative. With a still image that contains moving objects, the user can add and edit various motion effects by a simple but efficient user interface. As a result, the edited object conveys an effective motion effect without blurring the object. The proposed system is so user-friendly that novices can create motion photographs without any special skills. Furthermore, the extensible nature of the system means that new effects can be developed and plugged in. The experimental results and user study show that the proposed motion photography system can produce a variety of interesting motion photographs. Compared with general image editing tools (such as Photoshop), the proposed system can create high-quality motion photographs in a significantly shorter time.     

Tabletop computed lighting for practical digital photography

We apply simplified image-based lighting methods to reduce the equipment, cost, time, and specialized skills required for high-quality photographic lighting of desktop-sized static objects such as museum artifacts. We place the object and a computer-steered moving-head spotlight inside a simple foam-core enclosure and use a camera to record photos as the light scans the box interior. Optimization, guided by interactive user sketching, selects a small set of these photos whose weighted sum best matches the user-defined target sketch. Unlike previous image-based relighting efforts, our method requires only a single area light source, yet it can achieve high-resolution light positioning to avoid multiple sharp shadows. A reduced version uses only a handheld light and may be suitable for battery-powered field photography equipment that fits into a backpack.     

Will new chip revolutionize digital photography?

A company founded by well-known physicist, technologist, and inventor Carver Mead has developed a light-sensing chip that promises to radically change digital photography. Mead's company, Foveon, spent four years developing the X3 photographic sensor chip, which delivers two to four times the image resolution of other comparable digital-camera chips. Most digital cameras use charge-coupled-device technology. In the CCD process, light-sensitive integrated circuits store and display an image's data, converting each pixel into an electrical charge whose intensity corresponds to a specific color. These cameras use a mosaic filter with chip sensors that each detect just one color: red, green, or blue. Within the X3 chip, each sensor can detect red, green, and blue, depending on how far the captured light penetrates through layers of silicon-based color filters. The first X3-based cameras are scheduled to ship in the near future. National Semiconductor will build most of each chip, while Foveon will handle the final steps     

Fog effect for photography using stereo vision

Fog is an important factor in photography with a special aesthetic, emotional, or compositional meaning. We present a fog-simulation method for photo editing using binocular stereo vision. Given a stereo pair, we estimate the depth information by stereo matching followed by a process to refine depth results for the given photo editing purpose. Then, depth-aware fog effects can be applied on the base image, with optional interaction for control purposes. Besides homogeneous fog, we provide three tools to control the density of the fog media. Thus, various kinds of heterogeneous atmospheric effects can also been simulated. Experiments show that the proposed method can achieve more natural-looking results than manually drawn fog, our results are very close to the appearance of fog in the real world.     

Image capture pattern optimization for panoramic photography

Panoramic photography requires intensive operations of image stitching. A large quantity of images may lead to a rather expensive image stitching; while a sparse imaging may cause a poor-quality panorama due to the insufficient correlation between adjacent images. So, a good study for the balance between image quantity and image correlation may improve the efficiency and quality of panoramic photography. Therefore, in this work, we are motivated to present a novel approach to estimate the optimal image capture patterns for panoramic photography. We aim at the minimization of the image quantity which still preserves sufficient image correlation. We represent the image correlation as overlap area between the view range that can be separately observed from adjacent images. Moreover, a time-consuming imaging process of panoramic photography will result in a considerable illumination variation of the scene in images. Subsequently, the image stitching will be more challenged. To solve this problem, we design a series of imaging routines for our image capture patterns to preserve the content consistency, ensuring the generalization of our method to various cameras. Experimental results show that the proposed method can obtain the optimal image capture pattern in a very efficient manner. In these patterns, we can obtain a balanced image quantity but still achieve good results of panoramic photography.

     

Relative reflectance data from preprocessed multispectral photography

Abstract

Photographic image tone is an indicator of surface reflectance. If adequately preprocessed, photographic image tone can be used to provide a quantitative measureof relative surface reflectance,essential for many remotesensingapplications. The three preprocessing steps proposed are, first the standardization of the film data to a gamma of 1, second scene to scene ratioing, and third band to band ratioing. This methodology is reviewed and an example of its application provided in the preprocessing of a large multispectral photographic data set.     

Snow surface albedo estimation using terrestrial photography

A flexible and inexpensive remote sensing tool for albedo estimation using conventional terrestrial photography and its validation on an Alpine glacier are described. The proposed technique involves georeferencing oblique photographs to a digital elevation model (DEM), defining a mapping function between the information contained on a given pixel of the image and the corresponding cell of the DEM. This is attained by performing a perspective projection of the DEM after a viewing transformation into the camera coordinate system. Once the image is georeferenced, the reflectance values recorded by the film or digital camera are corrected for topographic and atmospheric influences and for the effect of the photographic process (lens-film-developing-scanning). Atmospheric transmittance is evaluated using the MODTRAN radiative transfer model. Diffuse and direct irradiation are estimated using a parametric solar irradiation model. The solar-ground geometry, anisotropy of reflected radiation, the effect of surrounding topography and the portion of visible sky are evaluated using terrain algorithms applied to the DEM. The response of the camera-film-scanner system is evaluated using an empirical approach. The result is a geographically correct map of normalized reflectance values. By comparing these to a surface of known albedo, the spatial distribution of albedos is calculated. Comparisons to in situ measurements on the Mer de Glace glacier, French Alps, show good agreement. Sources of error are identified and ways of improvement addressed. The georeferencing algorithm, implemented into the Interactive Data Language (IDL) is available from the author and at the user contributed IDL library at www.rsinc.com.     

A hierarchy of cameras for 3D photography

The view-independent visualization of 3D scenes is most often based on rendering accurate 3D models or utilizes image-based rendering techniques. To compute the 3D structure of a scene from a moving vision sensor or to use image-based rendering approaches, we need to be able to estimate the motion of the sensor from the recorded image information with high accuracy, a problem that has been well-studied. In this work, we investigate the relationship between camera design and our ability to perform accurate 3D photography, by examining the influence of camera design on the estimation of the motion and structure of a scene from video data. By relating the differential structure of the time varying plenoptic function to different known and new camera designs, we can establish a hierarchy of cameras based upon the stability and complexity of the computations necessary to estimate structure and motion. At the low end of this hierarchy is the standard planar pinhole camera for which the structure from motion problem is non-linear and ill-posed. At the high end is a camera, which we call the full field of view polydioptric camera, for which the motion estimation problem can be solved independently of the depth of the scene which leads to fast and robust algorithms for 3D Photography. In between are multiple view cameras with a large field of view which we have built, as well as omni-directional sensors.     

航拍磁带图像读取系统的研究与实现

航拍磁带图像读取系统主要用于读取记录了飞机上雷达所拍摄图像的磁带,通过计算机软硬件的结合,实现了记录在磁带上的数据的快速、准确读取以及相应的图像处理功能.该系统采用了最新的工控机配置,和工作站独立开来工作,极大地提高了磁带的读取速度.新的软件提供了更加人性化的界面,操作简洁方便,无需输入任何命令,只需用鼠标进行简单的点击就可完成所有的操作.     

新的大倾斜摄影的自动快速镶嵌模型

倾斜摄影往往导致地物较大的几何变形,难以直接利用传统的数字图像镶嵌方法进行镶嵌。提出了一种非常规的近似镶嵌模型,很好地保持了地物与观察者的相对位置关系及地物之间的大致位置关系,并且已经成功地应用于某军用航空相机远距离倾斜摄影的光学图像自动快速镶嵌系统。     

Projective texture atlas construction for 3D photography

The use of attribute maps for 3D surfaces is an important issue in geometric modeling, visualization and simulation. Attribute maps describe various properties of a surface that are necessary in applications. In the case of visual properties, such as color, they are also called texture maps. Usually, the attribute representation exploits a parametrization g:U??²→?³ of a surface in order to establish a two-dimensional domain where attributes are defined. However, it is not possible, in general, to find a global parametrization without introducing distortions into the mapping. For this reason, an atlas structure is often employed. The atlas is a set of charts defined by a piecewise parametrization of a surface, which allows local mappings with small distortion. Texture atlas generation can be naturally posed as an optimization problem where the goal is to minimize both the number of charts and the distortion of each mapping. Additionally, specific applications can impose other restrictions, such as the type of mapping. An example is 3D photography, where the texture comes from images of the object captured by a camera [4]. Consequently, the underlying parametrization is a projective mapping. In this work, we investigate the problem of building and manipulating texture atlases for 3D photography applications. We adopt a variational approach to construct an atlas structure with the desired properties. For this purpose, we have extended the method of Cohen–Steiner et al. [6] to handle the texture mapping set-up by minimizing distortion error when creating local charts. We also introduce a new metric tailored to projective maps that is suited to 3D photography.     

3D face computational photography using PCA spaces

In this paper, we present a 3D face photography system based on a facial expression training dataset, composed of both facial range images (3D geometry) and facial texture (2D photography). The proposed system allows one to obtain a 3D geometry representation of a given face provided as a 2D photography, which undergoes a series of transformations through the texture and geometry spaces estimated. In the training phase of the system, the facial landmarks are obtained by an active shape model (ASM) extracted from the 2D gray-level photography. Principal components analysis (PCA) is then used to represent the face dataset, thus defining an orthonormal basis of texture and another of geometry. In the reconstruction phase, an input is given by a face image to which the ASM is matched. The extracted facial landmarks and the face image are fed to the PCA basis transform, and a 3D version of the 2D input image is built. Experimental tests using a new dataset of 70 facial expressions belonging to ten subjects as training set show rapid reconstructed 3D faces which maintain spatial coherence similar to the human perception, thus corroborating the efficiency and the applicability of the proposed system.