A Novel Approach Based on Wavelet and Non-linear Transfer Function-Based Local Approach for Real Color Image Enhancement

In this paper, a novel wavelet-based dynamic range compression algorithm is proposed to improve the visual quality of digital images captured under non-uniform illumination condition. In the proposed method, an input RGB color image is converted to Hue-saturation-value (HSV) color image. The image enhancement technique is applied to the value component of the image, and saturation component is enhanced by stretching its dynamic range to get rich color display. The Hue component is preserved because change in the H component could change the color balance between HSV components. The wavelet transform technique is applied to the value component of the image. Wavelet transform is used especially for dimension reduction such that a dynamic range compression with local contrast enhancement algorithm is applied only to the approximation coefficients. The approximation coefficients are transformed using a non-linear transfer function and fallowed by the contrast enhancement process using the center-surround contrast enhancement method. The detail coefficients are also modified to prevent the edge distortion, then inverse wavelet transform is applied to the transformed V component of the image. The original H and enhanced saturation and value component of image are converted back to the RGB image.