Image forming apparatus

An image forming apparatus, comprising:

• a recording head configured to eject ink corresponding to an image to be printed, using arranged nozzles;
• and
• an ink-ejection-malfunction-nozzle detecting unit configured to detect an ink ejection malfunction nozzle among the nozzles;
• wherein the ink-ejection-malfunction-nozzle detecting unit (a) sets plural nozzle groups so as to be shifted sequentially by one nozzle such that each of the plural nozzle groups includes nozzles with a predetermined first interval among the arranged nozzles, (b) prints using the recording head a first test pattern that includes first bands respectively corresponding to the nozzle groups such that the first band includes thin lines respectively corresponding to the nozzles in the nozzle group, (c) sets plural nozzle subgroups so as to be shifted sequentially by one nozzle such that each of the plural nozzle subgroups includes nozzles with a predetermined second interval among the nozzles in each of the nozzle groups, (d) prints using the recording head a second test pattern that includes second bands respectively corresponding to the nozzle subgroups such that the second band includes thin blank lines respectively corresponding to the nozzles in the nozzle subgroup and a correction process is performed for adjacent pixels of the thin blank lines, (e) acquires a scanned image of the printed first test pattern and a scanned image of the printed second test pattern, (f) detects a first band including density defect in the scanned image of the first test pattern, (g) detects a second band not including density defect owing to the correction process in the scanned image of the second test pattern, among the plural second bands corresponding to the plural nozzle subgroups in the nozzle group of the detected first band and detects as the ink ejection malfunction nozzle a nozzle corresponding to the thin blank line in the second band not including density defect;
• and
• when detecting the second band not including density defect owing to the correction process, the ink-ejection-malfunction-nozzle detecting unit derives a total or an average value of pixel values of the plural second bands at each pixel position in the scanned image of the second test pattern, determines a reference range on the basis of the total or the average value, and detects the second band not including density defect owing to the correction process on the basis of density distributions of the reference range in the plural second bands.