Bioturbated heterolithic clastic reservoirs are often characterized by clean sandstones forming thin levels, small patches, and burrow infills. This scenario makes precise estimation of percentage of sandstone (net-to-gross) a very difficult task. At present, there are no tools available that allows a straightforward quantification of the sand content using core pictures. In this work, a novel technique that uses core photographs is presented. Using computer vision processing software it is possible to determine the composition of the analyzed cores from daylight pictures. The method is based on an automatic segmentation of contrasted core photographs and the subsequent analysis through image processing. This methodology allows precise estimation of the sandstone percentage and it is denominated Image Sandstone Analysis (ISA). A similar procedure was applied to ultraviolet core photographs to analyze and quantify oil impregnation. The method is called image fluorescence analysis (IFA). The results are continuous logs that can be fully integrated with other conventional core and well logs. The methodology was successfully applied to mature reservoirs. Three different logs were computed with sample rates of 1, 10 and 50 cm. In the case of ISA, the obtained logs proved to be useful tools for evaluating the location of sandier intervals, the precise calculation of net-to-gross for a desired interval, and the analysis of the internal cyclicity at different scales. IFA results were compared with other sophisticated well tools. The IFA log shows an excellent match with the oil saturation curve and provides a precise location of HC contacts. Both ISA and IFA logs also contribute to the precise estimation of core shift. Finally, there is a huge potential it the use of this novel tool to extract new information from existing photograms of core archives.