In Taiwan high schools, the current practice of traditional in-class lecture plus post-class unsupervised homework exercises for learning of advanced applied fields of Computer Science is in need of revamping. Teachers are teaching commercial software instead of working concepts to students. Lack of more suitable teaching materials and limited class time are the main reasons for the software based teaching practices. This study proposes a pre-class lecture video viewing plus in-class supervised lab work model that can circumvent above problems. Experiments on teaching of image processing concepts at two local high schools were conducted. Experimental results show that the proposed model is a feasible and effective way to teaching and for learning about image processing. The new approach also facilitated in class student-student and student-teacher interactions. Finally, students' understanding and interest in learning of Computer Science are also improved.