1. An image printing system configured for adjusting gloss on printed documents, the system comprising: a marking engine constructed to print images on a document, the printed images having gloss, a gloss measurement device comprising: (i) one or more illuminators configured to emit one or more light beams at the printed document, thereby producing generally specular reflectance and generally diffuse reflectance at least in a first direction; (ii) a linear array sensor configured to detect the generally specular reflectance and the generally diffuse reflectance in the first direction; a processor configured (a) to receive image data relating to a content of the image to be printed on the document; (b) to process the detected generally specular and diffuse reflectances to determine a characteristic of the gloss of the document, and (c) to compare the gloss characteristic with the image data relating to the content of the image printed on the document; and a controller configured to control at least one process controls parameter of the marking engine based on the comparison of the gloss characteristic with the image content by the processor.