Abstract:Borehole cameras are devices based on optical techniques to provide direct images of boreholes in the form of film or video. Advent of the panoramic technique led to viewing the entire section (360°) of the borehole wall,which is a panoramic image including current depth and compass direction. Digital technique,however,has been utilized to provide a powerful capability of forming,displaying and processing the images. The typical images are the unrolled image and the virtual 3D coregraph. All the images can be used not only to reveal the conditions in the borehole for qualitative identification but also to obtain pertinent information,especially for dip direction,dip angle and aperture of a crack,for quantitative analysis. The borehole camera technology has a wide application to geotechnique,engineering geology,hydraulic and civil engineering,petroleum industry,mining engineering and study on glaciers,etc.. The historical and current development status of the borehole camera technology(BCT) on technology and application are reviewed;and the technical features of devices in each stage,especially for the most representative system of development of the BCT-DBOT(digital borehole optical televiewer)are described. The comparisons of different devices for imaging principle,design of special light source,image processing,image display,image accuracy,etc. are studied;and the digital borehole optical televiewers (DPBCS,OPTV,OBI–40) are widely used in world according to different image processing methods,i. e.,ring by ring method and picture by picture method are distinguished. The merits and shortages of the two methods are illustrated;and the strength and potential development of the borehole camera technology are discussed.