# Contrast Sensitivity Based Multiscale Base-Detail Separation for Enhanced HDR Imaging
## 1 Introduction  
High dynamic range (HDR) imaging was introduced to record real-world radiance values, which can be at a much higher range than that of ordinary imaging devices. In real-world examples, the illumination levels cover at least 10 orders of magnitude, from a starlit night to a sunny afternoon [1]. Therefore, HDR imaging technology has been advanced for tone compression from the broad dynamic range to the 8-bit dynamic range for the common output of a display's dynamic range [2]. HDR tone mapping is a process of compressing the dynamic range of an image in order to display the HDR image on the display with a low dynamic range (LDR). Since the difference between the input and output dynamic range is very large, in order to preserve details, detail components are separated and preserved, or refined separately [3]. Therefore, the HDR image method uses a method of separating and processing the base layer and the detail layer of the image in order to effectively preserve the detailed image information. There are many base-detail separation methods. The bilateral filter is a representative edge-preserving filter that smooths an input image while preserving edges. It consists of spatial and intensity Gaussian filters. The spatial Gaussian filter controls the influence of distance pixels and the intensity Gaussian filter reduces the intensity difference at a pixel position. The bilateral filter was developed as the fast-bilateral filter (FBF) by [PERSON] and [PERSON] [4]. The FBF is designed to accelerate the bilateral filtering using a piecewise-linear approximation and sub-sampling. [PERSON] et al. proposed an adapting filter which follows the high-contrast edges of an image [5]. [PERSON] et al. proposed edge-adaptive layer blurring which includes the halo region estimation and compensation using the Gaussian difference to reduce the halo artifact caused by local tone mapping [6]. The color appearance model (CAM) predicts the perceived color properties of objects under different viewing conditions using a mathematical model based on the human visual system (HVS). The CAM is extended to iCAM06 to reproduce the HDR image [2] and it includes human visionproperties, such as chromatic adaptation and tone compression. [PERSON] et al. proposed a calibrated image appearance model to reproduce HDR images under different viewing and display conditions [7]. [PERSON] et al. proposed a compensation model for a white point shift of the iCAM06 by matching the channel gains of RGB cone responses before and after the tone compression process [8]. [PERSON] et al. proposed a global chromatic adaptation to reduce the desaturation effect in iCAM06 and chromatic adaptation (CA) - tone compression (TC) decoupling methods by reducing the interference between the chromatic adaptation and tone compression [9; 10]. Input data of the iCAM06 is XYZ, which is decomposed into a base layer, contains only large-scale variations, and a detail layer. The modules of chromatic adaptation and tone-compression processing are only applied to the base layer, thus preserving details in the image. For this processing, the iCAM06 uses the FBF that smooths the noise while preserving edge structures [4]. However, the iCAM06 uses the FBF which has a fixed edge-stopping function to preserve the details of an image while reducing the halo artifact. However, this causes the sharpness degradation of a rendered output image. This paper proposes a base-detail separation method and detail compensation technique for effective edge preserving using the visual contrast sensitivity function (CSF) property. The proposed method is conducted in a frequency domain of the FBF. The base layer is generated by multiplying the intensity layer and spatial kernel function, considering the frequency shift effect of the visual CSF in the FBF process. The detail layer is obtained by the difference between the input image and the base layer. After this, the detail layer is compensated by using the proposed sensitivity gain in the frequency domain.