This article combines the fractional differential theory with the total variation method and applies it to defining cultural industry image color matching. At the same time, we propose a new image color matching denoising model based on fractional partial differential equations. The model achieves simultaneous denoising in the time direction and the spaceplane. Experiments have proved that the fractional partial differential equations method has more advantages than integer-order partial differential equations in denoising and reducing step effects. It can effectively improve the contrast and clarity of image color matching in the cultural industry.
- Cultural industry
- Color matching
- Partial differential equations
- Optical depth
Under weather conditions such as rain, fog, and snow, the atmospheric scattering is severe, which results in the acquired natural scene images with poor color and contrast. WIR is not conducive to the extraction of image features. Most vision applications, including surveillance, tracking, intelligent navigation, intelligent vehicles, etc., need to extract image features  fully. This brings great difficulties to the normal operation of outdoor machine vision systems. Therefore, effectively removing the weather effect in the image is of great significance to improve the reliability and robustness of the visual system.
In recent years, natural scene image defogging restoration has gradually become a research hotspot in image processing and computer vision. The current restoration algorithms for images are mainly divided into two categories: one is based on image enhancement methods. For example, the histogram equalization technology is based on the moving template in the literature . Since the quality of the image is reduced exponentially with the distance from the scene point to the imaging sensor, this image enhancement technology that assumes a constant depth of field of the scene cannot well defog and restore the fogged image. If you know the precise scene depth and atmospheric condition information, you can easily restore the color and contrast of the ideal image. However, the degraded images acquired under realistic conditions do not have any additional calibration information for depth of field and atmospheric conditions. The lack of available information has brought great uncertainty to the restoration work. The defogging image recovery is an ill-posed inverse problem. In this paper, with the help of the physical model of fog formation, the energy optimization model of global defogging and local defogging of outdoor images is established .
This section uses two atmospheric scattering physical models to analyze the color and contrast of foggy images. These two scattering models will be used for defogging and restoration of degraded images. This is the basis of the algorithm in this article. The color of the scene point obtained by the color camera in the foggy weather is the linear combination of the sky color and the color of the scene point. Its mathematical expression is:
On a foggy day, the color and contrast degradation has an exponential relationship with the depth of field of the scene point. Therefore, the traditional color and contrast enhancement method that assumes the same depth of field of the scene point does not fully use the prior knowledge of degradation. It cannot remove the bad weather effect in the degraded image . Due to the insufficient amount of information for recovery, it has uncertainty. Based on the restoration as mentioned above algorithm of the atmospheric scattering physical model, we use simple additional information to construct a partial differential equation about the scene depth and image gradient to restore the ideal image.
In this section, an energy functional including scene depth and image gradient is constructed based on the physical model of fog formation. We formalize the defogging image restoration to minimize this energy function. We propose global and local dehazing models based on partial differential equations . The user's simple interactive operation is used to estimate the depth of field of the scene point to obtain the sky color, which can also eliminate the uncertainty in the restoration. This also realizes the defogging recovery from only a degraded image. The algorithm realizes interactive operation through a visual interface, which is simple and easy to operate in the algorithm. At the same time, local corrections can be made to improve the recovery effect of the global defogging model .
This section formalizes the defogging recovery problem to solve the partial differential equations about the scene depth and image gradient. The formula is expressed as ∇
The image defogging restoration problem is transformed into solving the partial differential equation shown in formula (6). However, the depth of field d and sky color
1. Select a sky area in the degraded image to obtain the brightness of the sky. The sky color vector and color direction are obtained if the degraded image is a color vector image.
First, select the approximate position of the vanishing point of the degraded image along the direction of increasing depth of field. The depth of field of a scene point has an inverse relationship with the image pixel distance from the scene point to the vanishing point. Secondly, input the scene points to approximate the maximum depth dmax and the minimum depth dmin, and interpolate the depth of field of the scene points. Here we can choose linear and non-linear interpolation. This article adopts the linear interpolation method. The specific formula is as follows
So far, the depth of field d and sky color
Solving equation (6) according to the boundary conditions can recover the ideal image
The global defogging restoration model has a good restoration effect for images with small changes in scene depth. When the scene depth changes greatly, equation (4) is not a good approximation to the ideal image gradient, and the scene depth gradient
In the global defogging model, it is assumed that the term
To improve the global defogging effect, the user can select the local area Ω
The image contrast degradation in fog is exponentially related to the optical depth of the scene point. Therefore, the optical depth of the local area can be increased when the contrast of the global restored image is still low. Otherwise, reduce the optical depth of the area. In this paper, the optical depth
The specific process of the image defogging restoration algorithm (see Figure 3) is as follows:
1. Obtain the scene depth and sky color of the degraded image. 2. Apply the global model to dehaze and restore. 3. Correct the optical depth of the area where the global restoration effect is not satisfactory to solve the local defogging model .
The following applies the algorithm of this paper to restore the degraded foggy image. The experimental results are shown in Figure 4. By gradually modifying the β value, the overall defogging recovery results can be revised as a whole. This can improve the dehazing effect.
Figure 4 shows that if the local defogging model continues to be used, the contrast of the local area of the image can be further improved.
This paper formalizes defogging recovery as solving partial differential equations about scene depth and image gradient to achieve defogging recovery from only one image. We can make local corrections to improve the defogging effect and smoothly integrate it into the global defogging recovery result until the application requirements are met. The defogging recovery of a single degraded image can be achieved better.