Image forming apparatus and image forming method

An image forming method comprising,

• forming, on a recording medium, a plurality of streaks based on predetermined image data, each of the plurality of streaks having an image density difference from an adjacent region that is a non-streak portion;
• reading brightness values of the non-streak portion and the plurality of streaks;
• detecting, based on the brightness values read by the reading,
• a first streak width of a first streak,
• a first brightness difference between a brightness value of the first streak and a brightness value of the non-streak portion corresponding to the first streak,
• a second streak width of a second streak wider than the first streak width, and
• a second brightness difference between a brightness value of the second streak and a brightness value of the non-streak portion corresponding to the second streak;
• calculating a correction coefficient corresponding to the first streak width based on the first brightness difference and the second brightness difference;
• and
• correcting image data of an image density value corresponding to the first streak width, based on the correction coefficient calculated by the calculator.