To successfully segment a transmission x-ray image the inherent blurring or structural unsharpness present in such an image must be taken into account. Initial work with an established wavelet-based segmentation algorithm resulted in an oversensitive performance with regard to the number of segmented regions detected. To improve on this performance, two segmentation algorithms are developed and tested. The approaches utilize a wavelet transform together with region merging and, alternatively, multilevel thresholding with region merging. These techniques outperform the ordinary wavelet method. Manually segmented images representing ground truth are used for a comparative evaluation of the segmentation techniques. Our work is part of an ongoing collaborative research program with the U.K. Home Office to analyze information extracted from dual-energy x-ray images for aviation security screening applications.