Unevenness of woven fabric results from irregularity of the yarn used as well as from the process of its manufacture(weaving). These unevenness and irregularities appear on fabric and will affect various fabric properties. Unevenness of plain textiles expresses itself not only as a variability of permeability or textiles thickness but also in their appearance. It shows as a fluttering, cloudy appearance with thicker and thinner places. The appearance of the plain textile is influenced by the irregularity of yarns from which the plain textile is made and by the textile manufacturing process, that is by weaving or knitting. In order to investigation of weft yarn mass irregularities on fabric surface unevenness and defects, various plain fabrics samples were prepared in which they differ only in weft yarn mass irregularity. One of the effective factors on fabric surface unevenness, is yarn protrusion in fabric structure. The protruding yarn from the body of a fabric is an important indicator of the mechanism of yarn interaction within the fabric and a predictor of fabric surface properties.The factors affecting protruding yarn are shown to fall in two main groups, one governing the structural characteristics of fabric and the other one, the mechanical properties of yarn. In this work, first relationship between weft yarn mass irregularities and fabric surface unevenness was investigated using angular power spectrum curve, a measure of yarn protrusion in fabric structures. The results showed a high significant correlation was observed between these two parameters. since fabric surface unevenness in that fabric image, as the brightness variation of fabric image is directly related to the fabric surface unevenness. Thus it can be pointed out that coefficient of variation between image gray levels is a measure of fabric surface unevenness.The image of fabric was first converted into grey scale. The image is divided into square fields so called unit area . and variation of greyness degree, depending on area of square field was calculated. The graphing gray levels coefficient of variation versus unit area was prepared, the results shows that fabric area-variation curve, indeed is a representation of fabric surface unevenness. By comparing samples area-variation curve it was observed that the more mass irregularities and coefficient of variation at weft yarn , the more its area-variation curve , which means to more fabric surface unevenness. Finally an unevenness criterion was introduced quantitative evaluation in order to fabric surface unevenness. The acquired area-variation curves are compared with each other and compared with visual evaluation of the woven fabric image. It was found that area-variation curves show only marked unevenness of woven fabric. The area-variation curve is a tool suitable for the quantification of surface unevenness on the basis of evaluation of a flat textile image. The surface unevenness expresses itself in the fabric appearance as the variation of flat textile colouration. The flat textile image is divided into squared fields and the fluctuation of colour shade (greyness degrees) is evaluated among individual squared fields by means of the area-variation curve.