变能量X射线成像执行过程中通过多管电压参数的设置，获取物体不同厚度范围的有效信息，并经图像融合处理获取反映物体内部完整结构信息的图像。但是由于物质的衰减系数和荧光转换效率均存在较强的能谱相关性，现有变能量成像方法中依据实验获取的管电压-厚度-器件响应曲线来确定子图加权系数的方法缺乏通用性，特别是对于多种材料复合的情况。对多电压情况下对应透照图像灰度的变化规律及关联关系进行研究，提出基于相邻管电压对应有效透照厚度重叠率约束的管电压递变步长控制方法；并提出灰度比例直方图的概念，实现子图加权系数的快速求解。多材质复合工件的变能量成像实验表明，该方法克服了现有变能量成像算法通用性方面的缺点，能够实现多材料复合情况下的有效子图融合。

X-ray radiographic imaging technology with variable energies acquires useful information of the object under tests in different thickness ranges by setting changing voltage parameters of the tubes. Such information are fused to show the complete internal structure of the object. In practical, the method to determine weighted coefficient of sub graphs based on tube voltage-thickness-device response curves in existing X-ray radiographic imaging experiments is passing out of current use, especially for composite materials. The reason is that the attenuation coefficient of the material and the fluorescence conversion efficiency of phosphor transform screen of materials are related to each other in energy spectra. A method of controlling varying steps of the tube voltages based on relations between adjacent tube voltages and effective transillumination thickness is presented by studying the gray changing rule of transillumination images under different voltages. And then, the proportion histogram is proposed to calculate the weighted coefficient. X-ray imaging of composite objects with variable energies shows experimentally that the mentioned method can realize fusion of effective sub-graphs of composite objects. It overcomes shortcomings of the existing image processing algorithms in X-ray radiographic imaging technology with variable energies.