To satisfy the demand for higher quality, manufacturers of LED print heads for electrophotography need effective measurement tools, both for quality and process control in production and for research and development. For LED printers, mid-tone gray-level uniformity is one of the key quality attributes. Because the print quality is very sensitive to print head performance, using carefully designed test targets with a commercially available image quality analysis system, LED print head quality can be quantified and characterized. This paper describes a measurement and diagnostic method of LED print heads and non-uniformity characterization using banding and line analysis tools. An advanced signal processing technique, discrete wavelet transform, was applied to decompose the signal and extract key information for LED print head quality. The correlation between vertical banding and LED print head defects will be discussed via a case study.