Deep neural networks are applied to a wide range of problems in recent years. In this work, Convolutional Neural Network (CNN) is applied to the problem of determining the depth from a single camera image (monocular depth). Eight different networks are designed to perform depth estimation, each of them suitable for a feature level. Networks with different pooling sizes determine different feature levels. After designing a set of networks, these models may be combined into a single network topology using graph optimization techniques. This "Semi Parallel Deep Neural Network (SPDNN)" eliminates duplicated common network layers, and can be further optimized by retraining to achieve an improved model compared to the individual topologies. In this study, four SPDNN models are trained and have been evaluated at 2 stages on the KITTI dataset. The ground truth images in the first part of the experiment are provided by the benchmark, and for the second part, the ground truth images are the depth map results from applying a state-of-the-art stereo matching method. The results of this evaluation demonstrate that using post-processing techniques to refine the target of the network increases the accuracy of depth estimation on individual mono images. The second evaluation shows that using segmentation data alongside the original data as the input can improve the depth estimation results to a point where performance is comparable with stereo depth estimation. The computational time is also discussed in this study.These authors contributed equally to this work.2 employ single camerase.g. security monitoring, automotive & consumer vision systems, and camera infrastructure for traffic and pedestrian management in smart cities. These and other smart-vision applications can greatly benefit from accurate monocular depth analysis. This challenge has been studied for a decade and is still an open research problem.Recently the idea of using neural networks to solve this problem has attracted attention. In this paper, we tackle this problem by employing a Deep Neural Network (DNN) equipped with semantic pixel-wise segmentation utilizing our recently published disparity post-processing method.This paper also introduces the use of Semi Parallel Deep Neural Networks (SPDNN). A SPDNN is a semi-parallel network topology developed using a graph theory optimization of a set of independently optimized CNNs, each targeted at a specific aspect of the more general classification problem. In 2 3 the effect of SPDNN approach on increasing convergence and improving model generalization is discussed. For the depth from monocular vision problem a fully-connected topology, optimized for fine features, is combined with a series of max-pooled topologies (2×2, 4×4 and 8×8) each optimised for coarser image features. The optimized SPDNN topology is re-trained on the full training dataset and converges to an improved set of network weights.It is worth mentioning that this network design strategy is not limited to the 'depth from monocular vision' problem, and...