Patent US 5,477,244

A table having a plurality of holding portions for holding recording heads to be tested is arranged to be pivotal between a printing position and a changing position, so that the recording head located at the changing position can be changed during estimation of the recording head located at the printing position. An estimation pattern in which dots are arranged so as not to contact each other is printed on a recording medium. The printed estimation pattern is read by an image pick-up device, and character amounts in units of dots are extracted from image data obtained by the image pick-up device. Pattern estimated values are calculated according to the dot character amounts and are used to judge whether the recording head is normal. Another printed pattern is read by the image pick-up device, and an edge image is extracted from density image data obtained by the image pick-up device. After enlargement/reduction processing is performed for the edge image, an edge image is extracted again. Shape character values in units of areas separated by edge lines of the edge image are obtained, and the pattern and any stain are discriminated based on the shape character values, thereby detecting a stain state. A one-dimensional average density in the line direction of the pattern is obtained from the density image data, and a line width is obtained based on the average density. A stain is detected on the basis of the line width.