This study establishes the relationship between image restoration and foggy days based on the atmospheric scattering model and restores the images according to the dark channel theory. For large-area dense fog and sky that do not conform to the prior assumption of dark primary color, the reason behind image distortion is analyzed, and the transmittance is corrected by introducing a tolerance parameter. As a result, the fog removal of the sky is not too difficult and the restoration of images with the sky is improved. This study sets an intensity threshold to avoid difficult defogging due to over high atmospheric light intensity. In addition, it adjusts the hue distribution of the restored image by an automatic color scale algorithm for a more natural image. Furthermore, the validation process of the image defogging algorithm is designed to obtain adjustable parameters. The subjective and objective performance verification and analysis of the three algorithms prove that the improved algorithm is better than the first two algorithms in defogging.