Percent Obscuration is a measure of the area percent covered by particles in a field of view. It can be estimated visually or measured computer assissted automated image analysis. Visual estimation can vary significantly from one analyst to another and even by the same analyst from one time to another. It has the advantage of speed. Computer assissted automated image analysis tends to be more accurate and more presice but is dependent upon the dection threshold and the size of the features in the field of view. The images below illustrate some of these effects.

The darkfield image above was analyzed as 0.8% obscuration using the threshold setting shown in the second image.

The brightfield image above was analyzed as 6.5% obscuration using the threshold setting shown in the second image.

This is the same field of view as the image calculated to have an obscuration of 6.5% but the detection is set slightly differently. The darkfield image above was analyzed as 8.7% obscuration using the threshold setting shown in the second image.