Abstract: An online system presents a user with a content item including an image and text. The online system overlays the text on the image if it predicts doing so will not render the text unreadable. To predict whether the overlay will render the text unreadable, the online system computes values describing various visual characteristics of a segment of the image on which the text may be overlaid and compares the values to corresponding threshold values. Based on the comparison, the online system predicts a readability of the text if overlaid on the segment. If the predicted readability is at least a threshold readability, the online system overlays the text on the segment of the image and presents the content item to the user with the text overlaid on the image. Otherwise, the online system presents the content item to the user with the text not overlaid on the image.

Abstract: An online system is configured to provide content items to users. The content item includes an image, and is displayed with a color block or colored border as an accent to the image. The color of the color block or colored bordered is dynamically selected based upon the image included in the content item, and is selected using a waterfall selection method comprising a sequence of different selection methods, each selection method configured to select a color based upon a most common color of the image that satisfies a respective set of selection criteria or determine that no color meets the respective set of selection criteria. The selection methods may comprise a dominant color selection method wherein the selected color corresponds to a most dominant color of the image, and a complementary color selection method wherein the select color is a complement of a dominant color of the image.