Impact of contrast modification on human feeling: an objective and subjective assessment

Images are powerful means of communication. Adding images to documents, websites, magazines, helps attracting the attention and providing an immediate feeling about the content of the document itself. At the same time, images can be used to influence the attitude of the reader. In the digital era it is easier than ever to create and share multimedia documents making extensive use of visual data. Furthermore, it is extremely easy to modify and adapt the images in order to make them more suitable to convey a concept. These modifications may simply consist in focusing the attention on a specific part of the image, to heavier manipulations such as changing the visual appearance or the contents to bias the opinion of the observer. This creates a rising interest for the availability of automatic blind tools able to detect possible modifications of images, and to correlate these modifications with the relevant impact on the viewer. This paper proposes an example of application of these concepts that exploits a tool for automatic detection of contrast modifications and analyzes their impact on human feeling. The results of instrumental and subjective studies are presented and discussed.