1. A computer-implemented method for detecting gloss non-uniformities on printed documents, wherein the method is implemented in a computer system comprising one or more processors configured to execute one or more computer program modules, the method comprising: printing a test pattern using a print engine, the test pattern having gloss; directing one or more light beams, using an illuminator, onto the test pattern to produce at least generally specular reflectance; scanning the test pattern, using a linear array sensor, to obtain image data, the image data including specular reflective image data that corresponds to the generally specular reflectance from the test pattern; and enhancing contrast of the specular reflective image data in darker or lower gray levels of the image data to facilitate detection of image quality non-uniformities in the gloss in the test pattern, wherein the enhancing contrast includes amplifying only the specular reflective image data in darker or lower gray levels of the image data, excluding all of the image data in light or higher gray levels that does not correspond to the gloss, into a dynamic range of the image data so as to detect and quantify the image quality non-uniformities in the gloss in the test pattern.