text: In this work, a fast Bilateral Solver for Quality Estimation Based multi-focus Image Fusion method (BS-QEBIF) is proposed. The all-in-focus image is generated by pixel-wise summing up the multi-focus source images with their focus-levels maps as weights. Since the visual quality of an image patch is highly correlated with its focus level, the focus-level maps are preliminarily obtained based on visual quality scores, as pre-estimations. However, the pre-estimations are not ideal. Thus the fast bilateral solver is then adopted to smooth the pre-estimations, and edges in the multi-focus source images can be preserved simultaneously. The edge-preserving smoothed results are utilized as final focus-level maps. Moreover, this work provides a confidence-map solution for the unstable fusion in the focus-level-changed boundary regions. Experiments were conducted on @math pairs of source images. The proposed BS-QEBIF outperforms the other @math fusion methods objectively and subjectively. The all-in-focus image produced by the proposed method can well maintain the details in the multi-focus source images and does not suffer from any residual errors. Experimental results show that BS-QEBIF can handle the focus-level-changed boundary regions without any blocking, ringing and blurring artifacts.
  @cite_43: A fast and effective image fusion method is proposed for creating a highly informative fused image through merging multiple images. The proposed method is based on a two-scale decomposition of an image into a base layer containing large scale variations in intensity, and a detail layer capturing small scale details. A novel guided filtering-based weighted average technique is proposed to make full use of spatial consistency for fusion of the base and detail layers. Experimental results demonstrate that the proposed method can obtain state-of-the-art performance for fusion of multispectral, multifocus, multimodal, and multiexposure images.
  @cite_9: Like bilateral filter (BF), cross bilateral filter (CBF) considers both gray-level similarities and geometric closeness of the neighboring pixels without smoothing edges, but it uses one image for finding the kernel and other to filter, and vice versa. In this paper, it is proposed to fuse source images by weighted average using the weights computed from the detail images that are extracted from the source images using CBF. The performance of the proposed method has been verified on several pairs of multisensor and multifocus images and compared with the existing methods visually and quantitatively. It is found that, none of the methods have shown consistence performance for all the performance metrics. But as compared to them, the proposed method has shown good performance in most of the cases. Further, the visual quality of the fused image by the proposed method is superior to other methods.
  @cite_45: Multi-focus image fusion has emerged as a major topic in image processing to generate all-focus images with increased depth-of-field from multi-focus photographs. Different approaches have been used in spatial or transform domain for this purpose. But most of them are subject to one or more of image fusion quality degradations such as blocking artifacts, ringing effects, artificial edges, halo artifacts, contrast decrease, sharpness reduction, and misalignment of decision map with object boundaries. In this paper we present a novel multi-focus image fusion method in spatial domain that utilizes a dictionary which is learned from local patches of source images. Sparse representation of relative sharpness measure over this trained dictionary are pooled together to get the corresponding pooled features. Correlation of the pooled features with sparse representations of input images produces a pixel level score for decision map of fusion. Final regularized decision map is obtained using Markov Random Field (MRF) optimization. We also gathered a new color multi-focus image dataset which has more variety than traditional multi-focus image sets. Experimental results demonstrate that our proposed method outperforms existing state-of-the-art methods, in terms of visual and quantitative evaluations.
  @cite_52: In this work, a quality estimation based multi-focus image fusion method (QEBIF) is proposed. In this method, the all-in-focus image is generated by pixel-wise summarizing the multi-focus images with their estimated focus levels as weights. Since the visual quality of an image is highly correlated with its focus level, the visual quality is estimated to be the pre-measurements of focus levels. Via the guided filter, the pre-measurements are smoothed to form the final-measurement with edges in the multi-focus images preserved simultaneously. In addition, the confidence map is proposed to measure the reliability of different local regions. Experiments show that QEBIF method outperforms the other fusion methods, and its fusion results can well maintain the detailed information in the multi-focus images without suffering the ringing or blocking artifacts.
summary: Besides, different edge-preserving smoothing filters were explored in earlier works to make full use of spatial consistency during the fusion process. CBF @cite_9 adopts the cross bilateral filter (CBF) to compute the weights to measure the strength of details in multi-focus source images. Li @cite_43 , Nejati @cite_45 and Guan @cite_52 adopted the guided filter to do the fusion. In this work, a recent proposed state-of-the-art edge-preserving smoothing filter, the fast bilateral solver, is first adopted in image fusion task. Moreover, the confidence map is proposed to help the focus-level estimation with the fast bilateral solver in BS-QEBIF.