Image enhancement by histogram equalization reduces the number of gray levels that lead to information loss and unnatural appearance. This paper aims to improve the contrast and preserve information and edge details by employing gradient-based joint histogram equalization. It is achieved by a multiscale-based dark pass filter, which gives the pixel’s edge information. A joint histogram is computed from the edge information and the gray-level distribution of the low contrast image to develop a discrete function. This discrete function is mapped to uniform distribution to get the final enhanced image. The proposed method is experimented on Kodak, USC-SIPI, and CSIQ databases and analyzed using various performance measures such as Contrast, standard deviation, contrast improvement index, structural similarity index, normalized entropy, and normalized mean brightness error. It is observed that the proposed method provides the highest Contrast values of 86.2, 85.79, and 86.02 in Kodak, USC-SIPI, and CSIQ databases, respectively. Normalized entropy value is found to be highest for the proposed method for all the databases. This is noticed to be 0.89, 0.84, and 0.85 for the databases Kodak, USC-SIPI, and CSIQ, respectively. The degree of the uniform distribution is measured by Kullback–Leibler distance. The proposed method produces more uniformity than other techniques available in the literature for all the three databases.

通过直方图均衡化进行图像增强可以减少导致信息丢失和不自然外观的灰度级数量。本文旨在通过采用基于梯度的联合直方图均衡化来提高对比度并保留信息和边缘细节。这是通过基于多尺度的暗通滤波器实现的，该滤波器可以提供像素的边缘信息。根据边缘信息和低对比度图像的灰度分布计算联合直方图，以开发离散函数。将此离散函数映射到均匀分布，以获得最终的增强图像。将该方法在Kodak，USC-SIPI和CSIQ数据库上进行了实验，并使用各种性能指标进行了分析，例如对比度，标准差，对比度改善指数，结构相似性指数，归一化熵，和归一化的平均亮度误差。可以看出，所提出的方法在柯达，USC-SIPI和CSIQ数据库中分别提供了86.2、85.79和86.02的最高对比度值。对于所有数据库，该方法的归一化熵值最高。对于数据库柯达，USC-SIPI和CSIQ，这分别是0.89、0.84和0.85。均匀分布的程度由Kullback-Leibler距离测量。对于所有的三个数据库，所提出的方法比文献中提供的其他技术具有更高的一致性。对于所有数据库，该方法的归一化熵值最高。对于数据库柯达，USC-SIPI和CSIQ，这分别是0.89、0.84和0.85。均匀分布的程度由Kullback-Leibler距离测量。对于所有的三个数据库，所提出的方法比文献中提供的其他技术具有更高的一致性。对于所有数据库，该方法的归一化熵值最高。对于数据库柯达，USC-SIPI和CSIQ，这分别是0.89、0.84和0.85。均匀分布的程度由Kullback-Leibler距离测量。对于所有的三个数据库，所提出的方法比文献中提供的其他技术具有更高的一致性。