Recently, several algorithms have been developed to hide data in either text images or halftone images. According to an observation that the number of transitions between black pixel and white pixel in the halftone image is much larger than that in the text image, this paper presents a unified min-max transition (MMT) scheme to embed data into the above two types of images without visual degradation. For text (halftone) images, data hiding can be performed by modifying the values of pixels to minimize (maximize) the number of the transitions. Based on our proposed MMT scheme, a unified block- and MMT-based data hiding (BMMTDH) algorithm is developed for text images, halftone images, and mixed text/halftone (MTH) images. Experimental results demonstrate that for MTH images, our proposed BMMTDH algorithm outperforms the previous relevant algorithms.