Experimental studies on fracture flow processes are vital to understand the dependence of fracture permeability on various complex processes. A key parameter in such experiments is the fracture aperture, which can be determined using light transmission techniques when using transparent fracture models. For this, scientific-grade monochrome cameras are used to record light intensity under different conditions. The output data of scientific cameras is linearly related to the radiance scene, which allows one to do quantitative analysis using such data. On the contrary, consumer-grade digital (CGD) cameras usually output nonlinear color images (e.g. JPG or TIFF files), which are not suitable for most scientific uses. In this paper, we outline an image analysis procedure to use CGD cameras for light intensity measurements. We demonstrate that the direct use of raw data from such cameras is adequate for scientific quantification and prevents the introduction of artefacts from further image processing that usually occurs within the built-in software of most cameras.